EXHIBIT 10.65
                                                                -------------


                            STOCK PURCHASE AGREEMENT

                             FOR THE ACQUISITION OF

                        MOTOROLA ARDIS ACQUISITION, INC.

                                       AND

                              MOTOROLA ARDIS, INC.

                                       BY

                         AMSC ACQUISITION COMPANY, INC.

                            A WHOLLY-OWNED SUBSIDIARY

                                       OF

                      AMERICAN MOBILE SATELLITE CORPORATION






                          Dated as of December 31, 1997













                                TABLE OF CONTENTS

                                                                            Page

ARTICLE 1.  DEFINITIONS..................................................      1

ARTICLE 2.  MERGER, PURCHASE AND SALE OF SHARES..........................     13

        Section 2.1               Merger, Purchase and Sale
                                  of Shares       .......................     13
        Section 2.2               MAI Purchase Price and MAA
                                  Purchase Price.........................     14
        Section 2.3               Purchase Price Adjustments.............     14
        Section 2.4               Post-Closing Purchase Price
                                  Adjustment.............................     15
        Section 2.5               Closing Place, Date and Time...........     17
        Section 2.6               FCC Authorization and Final Order......     17
        Section 2.7               Deliveries at Closing..................     18
        Section 2.8               Deliveries Post-Closing................     20

ARTICLE 3.  REPRESENTATIONS AND WARRANTIES
                OF SELLER................................................     20

        Section 3.1               Organization and Good Standing.........     20
        Section 3.2               Authority; No Required Consents
                                  or Governmental Authorizations;
                                  No Breach of Statute or Contract;
                                  Enforceability.........................     21
        Section 3.3               Ownership of Shares....................     23
        Section 3.4               Capitalization of MAA, MAI
                                  and the Subsidiaries...................     23
        Section 3.5               Corporate Records......................     23
        Section 3.6               Employee Benefit Plans.................     24
        Section 3.7               Broker's or Finder's Fees..............     26
        Section 3.8               Financial Statements...................     26
        Section 3.9               Accounts Receivable....................     27
        Section 3.10              Absence of Undisclosed
                                  Liabilities............................     27
        Section 3.11              Existing Condition.....................     28
        Section 3.12              Title to Properties; Leasehold
                                  Interests..............................     30
        Section 3.13              Condition of Tangible Assets...........     30
        Section 3.14              Books of Account.......................     31
        Section 3.15              Litigation.............................     31
        Section 3.16              Compliance with Law....................     31
        Section 3.17              Environmental Matters..................     32
        Section 3.18              Insurance..............................     32
        Section 3.19              Contracts and Commitments..............     33
        Section 3.20              Additional Information.................     34
        Section 3.21              Intellectual Property..................     35
        Section 3.22              No Third Party Options.................     37
        Section 3.23              Tariffs; FCC Licenses;
                                  Non-FCC Authorizations.................     37
        Section 3.24              Officer and Employee Compensation......     39
        Section 3.25              Indebtedness...........................     39
        Section 3.26              Access; Sophistication; etc............     39
        Section 3.27              Investment Representation..............     40


ARTICLE 4.  REPRESENTATIONS AND WARRANTIES OF
                AMSC AND PURCHASER.......................................     41

        Section 4.1               Organization and Good Standing.........     41
        Section 4.2               Authority; No Required Consents
                                  or Governmental Authorizations
                                  or Breach of Statute or
                                  Contract; Enforceability...............     41
        Section 4.3               Broker's or Finder's Fees..............     43
        Section 4.4               Access; Sophistication; etc............     43
        Section 4.5               Investment Representation..............     43
        Section 4.6               SEC Filings; Financial
                                  Statements.............................     44
        Section 4.7               Absence of Certain Changes.............     45
        Section 4.8               Absence of Undisclosed
                                  Liabilities............................     45
        Section 4.9               Litigation.............................     45


ARTICLE 5.  CERTAIN AGREEMENTS...........................................     46

        Section 5.1               Conduct of the Business................     46
        Section 5.2               Access to Information..................     49
        Section 5.3               Efforts; Further Assurances;...........     49
                                  Permits
        Section 5.4               Books and Records......................     50
        Section 5.5               Governmental Regulatory
                                  Approvals..............................     50
        Section 5.6               FCC Consent............................     51
        Section 5.7               HSR Act Review.........................     51
        Section 5.8               Registration Rights....................     51
        Section 5.9               Lock-up................................     51
        Section 5.10              Nonsolicitation........................     52
        Section 5.11              IBM Contract Renewal...................     52
        Section 5.12              UPS Contract...........................     52
        Section 5.13              Escrow Agreement.......................     52
        Section 5.14              Employee Transition....................     53
        Section 5.15              Updated Disclosure Schedule............     53
        Section 5.16              Nextel Proceeds........................     53
        Section 5.17              Non-Vendor Intercompany Financing
                                  Arrangements...........................     53
        Section 5.18              Intercompany Agreements................     54



ARTICLE 6.  CONDITIONS TO CLOSING........................................     54

        Section 6.1               Conditions to Obligation of
                                  Purchaser..............................     54
        Section 6.2               Conditions to Obligations of
                                  Seller..        .....................       56

ARTICLE 7.  INDEMNIFICATION..............................................     58

        Section 7.1               Indemnification by Seller..............     58
        Section 7.2               Indemnification by AMSC................     59
        Section 7.3               Limitations on Indemnification for
                                  Breaches of Representations and
                                  Warranties.............................     59
        Section 7.4               Survival of Representations and
                                  Warranties.............................     60
        Section 7.5               Method of Asserting Claims.............     60
        Section 7.6               Method of Payment......................     62
        Section 7.7               Limitation of Recourse.................     63
        Section 7.8               Acknowledgment by Seller, Purchaser
                                  and AMSC        .......................     63


ARTICLE 8.  TAX MATTERS..................................................     64

        Section 8.1               Seller's Tax Representations
                                  and Warranties.........................     64
        Section 8.2               AMSC's Tax Representations
                                  and Warranties.........................     66
        Section 8.3               Tax Returns, Audits, Contests, Etc.;
                                  Tax Cooperation; Tax Sharing
                                  Agreements; Tax Records................     68
        Section 8.4               Asset Purchase Treatment
                                  for MAI Shares.........................     72
        Section 8.5               Tax-Free Reorganization
                                  Treatment..............................     76
        Section 8.6               Transfer Taxes.........................     76
        Section 8.7               General Tax Indemnifications...........     76
        Section 8.8               Exclusive Remedy for Taxes.............     81
        Section 8.9               Survival and Purchase Price
                                  Adjustment.............................     81

ARTICLE 9.  TERMINATION OF AGREEMENT; PAYMENT OF
                EXPENSES; WAIVER OF CONDITIONS...........................     82

        Section 9.1               Termination Pre-Agreement..............     82
        Section 9.2               Termination Post-Closing...............     83
        Section 9.3               Payment of Expenses; Waiver of
                                  Conditions.............................     84

ARTICLE 10.  MISCELLANEOUS...............................................     84

Section 10.1                      Amendments.............................     84
Section 10.2                      Further Instruments and
                                  Assurances.............................     84
Section 10.3                      Public Announcements...................     85
Section 10.4                      Governing Law..........................     85
Section 10.5                      Notices         .......................     85
Section 10.6                      Assignment and Binding Effect..........     86
Section 10.7                      Entire Agreement.......................     86
Section 10.8                      Severability...........................     87
Section 10.9                      Counterparts...........................     87
Section 10.10                     No Third Party Beneficiaries...........     87
Section 10.11                     Delays or Omissions....................     87
Section 10.12                     Construction...........................     87
Section 10.13                     Knowledge Standard.....................     88
Section 10.14                     Expenses        .......................     88
















                                    EXHIBITS

Exhibit

A                                 AMSC Warrants

B                                 Registration Rights Agreement





                                 






                            STOCK PURCHASE AGREEMENT


             THIS STOCK PURCHASE  AGREEMENT  (this  "Agreement")  is dated as of
December  31, 1997 and is entered into by and among  MOTOROLA,  INC., a Delaware
corporation ("Seller"),  MOTOROLA ARDIS ACQUISITION, INC. a Delaware corporation
("MAA"),  and MOTOROLA ARDIS, INC. a Delaware  corporation ("MAI"), and American
Mobile  Satellite  Corporation,   a  Delaware  corporation  ("AMSC"),  and  AMSC
Acquisition Company, Inc., a Delaware corporation ("Purchaser").


                             ARTICLE 1. DEFINITIONS.

            Section 1.1  Definitions.
                         -----------

            "Acquisition Proposal" has the meaning set forth in Section 5.9.

            "Adverse Legal Opinion" has the meaning set forth in Section 2.6(a).

            "Affiliate" shall mean with respect to any Person, any other Person
that is  directly  or  indirectly  controlling,  controlled  by or under  common
control  with such  Person or  entity or any of its  subsidiaries,  and the term
"control"  (including the terms "controlled by" and "under common control with")
means having, directly or indirectly, the power to direct or cause the direction
of the management and policies of a Person,  whether through ownership of voting
securities or by contract or otherwise

            "Affiliated Group" shall  mean  an "affiliated group" as defined in
Section 1504(a) of the Code.

            "Agreement" has the meaning set forth in the introductory paragraph
hereof.

            "AMSC Common  Stock" shall mean the common  stock,  par value $0.01
per share, of AMSC.

            "AMSC Group" shall mean any Affiliated  Group  including  AMSC, any
successor  thereof or, if such Affiliated  Group shall cease to exist,  AMSC and
any successors thereto.

            "AMSC  Shareholder  Approval" has  the meaning set forth in Section
2.7(a)(iv).

            "AMSC  Warrants"  shall  mean  warrants  issued  by AMSC to  Seller
substantially in the form attached hereto as Exhibit A.

            "ARDIS" means ARDIS Company.

            "ARDIS Balance Sheet" shall mean the unaudited consolidated balance
sheet of ARDIS Holding as of September 30, 1997.

            "ARDIS Balance Sheet Date" has the meaning set forth in Section 3.8.

            "ARDIS Holding" means ARDIS Holding Company.

             "Benefit  Plan"  shall  mean any plan,  agreement,  arrangement  or
commitment  which  is  an  employment  or  consulting  agreement,  executive  or
incentive   compensation  plan,  bonus  plan,  retention  bonus  plan,  deferred
compensation agreement,  employee pension, profit sharing, savings or retirement
plan,  employee  stock  option  or stock  purchase  plan,  group  life,  health,
disability,  sick pay or accident  insurance  or other  employee  benefit  plan,
agreement, arrangement or commitment,  including, without limitation, severance,
holiday,  vacation,  Christmas or other bonus plans (including,  but not limited
to, employee benefit plans, as defined in Section 3(3) of ERISA), maintained for
the benefit of any employee or director or former employee or former director of
MAA, MAI or any of the Subsidiaries whether or not maintained by MAA, MAI or any
of the Subsidiaries or with respect to which MAA, MAI or any of the Subsidiaries
makes or has any obligation to make contributions.

             "Books and Records" shall mean all of MAA's,  MAI's and each of the
Subsidiaries'  customer or  subscriber  lists and records,  accounts and billing
records  (including a copy of the detailed  general ledger and the summary trial
balances,  where available),  detailed  continuing  property records,  equipment
records,  plans,  blueprints,   specifications,   designs,  drawings,   surveys,
engineering  reports,   personnel  records  (where  applicable)  and  all  other
documents,  computer data and records  (including  records and files on computer
disks or stored electronically) relating to the Subsidiaries.

             "Business Day" means any day other than  Saturday,  Sunday or a day
that  constitutes  a legal  holiday in the State of Illinois or the  District of
Columbia.

             "CERCLA"  shall  mean  the  Comprehensive  Environmental  Response,
Compensation and Liability Act of 1980, as amended.

             "Claim Notice" has the meaning set forth in Section 7.5(a).

             "Closing" has the meaning set forth in Section 2.5.

             "Closing Cash Payment" has the meaning set forth in Section 2.3.

             "Closing Date" has the meaning set forth in Section 2.5.

             "Closing  Financial   Statements"  shall  mean  (i)  the  unaudited
consolidated  income statement and statement of cash flows for ARDIS Holding for
the period from January 1, 1998 through the Closing Date and (ii) the  unaudited
consolidated balance sheet for ARDIS Holding effective as of the Closing Date.

             "Closing Stock Payment" has the meaning set forth in Section 2.3.

             "Closing Working Capital" has the meaning set forth in Section 2.3.

             "Code" shall mean the Internal Revenue Code of 1986, as amended.

             "Collateral   Agreements"   shall  mean  the  Registration   Rights
Agreement,  the Escrow Agreement and all such other  agreements  entered into by
the parties hereto in connection with the transactions contemplated hereby.

             "Common  Stock"  shall  mean the common  stock,  par value $.01 per
share, of MAA and the common stock, par value $.01 per share, of MAI.

             "Companies" shall mean MAA, MAI and the Subsidiaries.

             "Company" shall mean any one of the Companies.

             "Consideration Shares" has the meaning set forth in Section 2.2.

             "Control"  shall  mean  the  power to  direct  the  management  and
policies of a Person,  directly or indirectly,  whether through the ownership of
voting  securities,  by contract or otherwise;  and the terms  "controlling" and
"controlled" shall have meanings correlative to the foregoing.

             "Cumulative  Temporary  Differences" means the differences  between
the bases in assets  and  liabilities  for  Financial  Statement  and income Tax
purposes that will result in the recognition of different  amounts of income and
expense for Financial Statement and income Tax purposes in future periods.

             "Disclosure Schedule" shall mean the Disclosure Schedule, including
the Introduction thereto,  delivered simultaneously herewith by Seller and dated
as of even date herewith.

             "Environmental  Conditions" shall mean any and all acts, omissions,
events, circumstances, and conditions,  including any pollution,  contamination,
degradation,  damage,  or injury  caused by,  related to, or arising  from or in
connection with the generation,  use, handling,  treatment,  storage,  disposal,
discharge, emission or release of Hazardous Materials.

             "Environmental  Laws"  shall  mean  all  federal,  state,  local or
municipal laws, rules,  regulations,  statutes, and ordinances and orders of any
Governmental Entity relating to (a) the control of any potential  pollutant,  or
protection  of the air,  water or land,  (b)  solid,  gaseous  or  liquid  waste
generation,  handling, treatment,  storage, disposal or transportation,  and (c)
exposure  to  hazardous,  toxic  or  other  substances  alleged  to be  harmful.
"Environmental  Laws" shall  include the Clean Air Act, the Clean Water Act, the
Resource   Conservation   and  Recovery  Act,  the  Superfund   Amendments   and
Reauthorization  Act, the Toxic Substances  Control Act, the Safe Drinking Water
Act, and the CERCLA, and shall also include all state, local and municipal laws,
rules,  regulations,  statutes,  ordinances  and orders dealing with the subject
matter of the above listed federal  statutes or promulgated by any  governmental
or  quasi-governmental  agency  thereunder in order to carry out the purposes of
any federal, state, local or municipal law.

             "Environmental  Liabilities"  shall  mean any and all  liabilities,
responsibilities,  claims,  suits, losses,  costs (including remedial,  removal,
response,  abatement,  clean-up,  investigative  and/or monitoring costs and any
other related costs and expenses),  other causes of action  recognized now or at
any later time, damages,  settlements,  expenses, charges,  assessments,  liens,
penalties,  fines, pre-judgment and post-judgment interest,  attorneys' fees and
other legal costs  incurred or imposed  (a)  pursuant to any  agreement,  order,
notice  of   responsibility,   directive   (including   directive   embodied  in
Environmental  Laws),  injunction,  judgment  or  similar  documents  (including
settlements)  arising out of, in connection with, or under  Environmental  Laws,
(b) pursuant to any claim by a Governmental  Entity or other Person for personal
injury, property damage, damage to natural resources, remediation, or payment or
reimbursement of response costs incurred or expended by such Governmental Entity
or Person pursuant to common law or statute, or (c) as a result of Environmental
Conditions.

             "ERISA" shall mean the Employee  Retirement  Income Security Act of
1974, as amended.

             "ERISA Affiliate" shall mean any person, firm or entity (whether or
not  incorporated)  which, by reason of its relationship with MAA, MAI or any of
the  Subsidiaries,  is required  to be  aggregated  with MAA,  MAI or any of the
Subsidiaries  under Sections 414(b),  (c) or (m) of the Code or which,  together
with MAA,  MAI or any of the  Subsidiaries,  is a member of a  controlled  group
within the meaning of Section 4001(a) of ERISA.

             "Escrow  Agent" shall mean a national  banking  association,  trust
company or similar entity mutually acceptable to the parties.

             "Escrow  Agreement"  shall  mean an escrow  agreement  by and among
Seller,  Purchaser, AMSC and the Escrow Agent containing such terms as are usual
and  customary  for  similar  documents  used  in  similar  circumstances,   and
containing specifically the following terms:

               (a) Upon consummation of the financing contemplated under Section
               6.1(l)  hereof,  Purchaser  shall deposit all of the net proceeds
               thereof with the Escrow Agent (the "Escrowed Funds");

               (b) Prior to the Closing,  the Escrowed Funds shall be maintained
               for the benefit of Purchaser,  with the interest accruing thereon
               until the Closing Date being allocated to Purchaser;

               (c) Upon  Closing,  (i) the MAI  Purchase  Price  portion  of the
               Escrowed  Funds  shall be  maintained  for the benefit of Seller,
               with the  interest  accruing on such amount  beginning  as of the
               Closing  Date being  allocated  to Seller (the  "Seller  Escrowed
               Funds"),  and (ii) the remainder of the Escrowed Funds (including
               any interest  accrued on the Escrowed  Funds prior to the Closing
               Date) shall be maintained for the benefit of Purchaser,  with the
               interest  accruing on such  remaining  amount of  Escrowed  Funds
               beginning  as of the Closing  Date being  allocated  to Purchaser
               (the "Purchaser Escrowed Funds");

               (d) Upon issuance of a Final Order from the FCC granting  consent
               with respect to the FCC Authorization,  the Seller Escrowed Funds
               shall be  released  to Seller and the  Purchaser  Escrowed  Funds
               shall be released to Purchaser;

               (e) In the event of a termination of this  Agreement  pursuant to
               Article 9, all of the  Escrowed  Funds  (including  all  interest
               accrued thereon) shall be released to Purchaser.

             "Estimated Working Capital" has  the meaning  set forth in  Section
2.3.

             "FCC" shall mean the Federal Communications Commission.

             "FCC Authorization" has the meaning set forth in Section 2.6(a).

             "FCC Consents" has the meaning set forth in Section 5.6.

             "FCC Licenses"  shall mean all licenses,  certificates,  permits or
other  authorizations  granted to MAA, MAI or any of the Subsidiaries by the FCC
that are used in the conduct of the business of MAA, MAI or the Subsidiaries.

             "Final Order" shall mean an action or decision as to which:  (1) no
request for a stay is pending, no stay is in effect, and any deadline for filing
such request that may be designated by statute or regulation has passed;  (2) no
petition for rehearing or  reconsideration  or application for review is pending
and the time for filing any such petition or application has passed; (3) the FCC
(or  comparable  body  exercising  jurisdiction)  does not have  the  action  or
decision  under  reconsideration  on its own motion and the  specified  time for
initiating such  reconsideration  has passed; and (4) no appeal is pending or in
effect and any  deadline  for filing any such appeal that may be  designated  by
statute or rule has passed.

             "Final Payment" has the meaning set forth in Section 2.4.

             "Financial  Statements" shall mean the consolidated  balance sheets
of ARDIS  Holding as of December 31, 1997,  December 31, 1996,  and December 31,
1995, the related  statements of income and retained  earnings and notes thereto
for the 12-month periods then ended,  examined by Price Waterhouse,  LLP (or, in
the case of those for 1997,  KPMG Peat Marwick),  independent  certified  public
accountants, and the unaudited consolidated balance sheet of ARDIS Holding as of
September  30,  1997 and the  related  consolidated  statements  of  income  and
retained earnings for the 9-month period then ended.

             "GAAP"  shall  mean   generally   accepted  accounting  principles,
consistently applied.

             "Governmental  Entity"  shall  mean any public  body or  authority,
including courts of competent jurisdiction, domestic or foreign.

             "Hazardous  Materials"  shall mean any (a)  petroleum  or petroleum
products,  (b) hazardous  substances as defined by ss. 101(14) of CERCLA and (c)
any other  chemical,  substance or waste that is  regulated by any  Governmental
Entity under any Environmental Law.

             "HSR Act" shall mean the Hart-Scott-Rodino  Antitrust  Improvements
Act of 1976, as amended.

             "Indemnification  Threshold  Amount"  has  the meaning set forth in
Section 7.3(a).

             "Indemnitee" has the meaning set forth in Section 7.5.

             "Indemnitor" has the meaning set forth in Section 7.5.

             "Intellectual  Property" shall mean all of the following throughout
the universe:  (i) patents and patent applications and all forms and equivalents
thereof,  including  divisions,  continuations,  continuations-in-part,  utility
patents, design patents, extensions, reissued and reexamined patents, patents of
addition,  confirmation patents, importation patents,  registration patents, and
inventor's  certificates;  (ii)  rights to file  patent  applications  and other
interests in inventions and discoveries,  whether reduced to practice or not, on
which no patent application has been filed; (iii) copyrights and all related and
equivalent rights, including copyright registrations, applications for copyright
registration,  moral rights, and neighboring  rights;  (iv) common law and other
trademarks,  trade names,  trade dress, and service marks, and registrations and
applications for registration  thereof;  (v) rights in industrial designs,  mask
works, and registrations and applications for registration  thereof;  (vi) trade
secrets;  (vii)  methods,  processes,   computer  software,  designs,  drawings,
laboratory  notebooks,  technical data, research and development data, know-how,
market reports, consumer investigations,  product surveys, distribution methods,
and customer  lists;  (viii)  licenses to or under and shop rights in any of the
foregoing; and (ix) all other proprietary information;  provided,  however, that
the term  "Intellectual  Property"  shall not  include any  generally  available
"off-the-shelf"  software purchased for use in the day-to-day  operations of the
Companies.

             "Interim  Financial  Statement"  shall mean the ARDIS Balance Sheet
and the related  consolidated  statements  of income and  retained  earnings and
notes thereto for the 9-month period then ended.

             "Lien" shall mean, with respect to any asset,  any mortgage,  lien,
pledge, charge,  security interest or encumbrance of any kind in respect of such
asset.

             "Litigation"  shall mean,  with respect to any Person,  any action,
claim,  demand,  suit,  proceeding,  citation,  summons,  subpoena,  inquiry  or
investigation of any nature, civil, criminal, regulatory or otherwise, in law or
in equity,  pending or threatened against, by or affecting such Person or any of
its properties or assets, by or before any court, tribunal,  arbitrator or other
Governmental Entity.

             "Lock-up Period" has the meaning set forth in Section 5.9.

             "Losses" has the meaning set forth in Section 7.1.

             "MAA Purchase Price" has the meaning set forth in Section 2.2(B).

             "MAA Shares"  shall mean all of the shares of capital  stock of MAA
outstanding immediately prior to the Closing.

             "MAI Purchase Price" has the meaning set forth in Section 2.2(A).

             "MAI Shares"  shall mean all of the shares of capital  stock of MAI
outstanding immediately prior to the Closing.

             "Management  Employee"  shall mean the key managers of ARDIS, to be
designated by Seller prior to the time  Purchaser's  obligations to Seller arise
under the last sentence of Section 5.14 herein, not to exceed 12 employees.

             "Market  Value" shall mean the average of the closing prices of the
AMSC Common Stock on the Nasdaq Stock Market (National Market System) for the 20
trading days immediately preceding the date of such calculation.

             "Material  Adverse Effect" shall mean a material  adverse effect on
MAA, MAI and the Subsidiaries, taken as a whole.

             "Material Adverse Change"  shall mean a material  adverse change in
the  business,  operation,   assets,  properties,  or  condition  (financial  or
otherwise) of MAI, MAA and the Subsidiaries, taken as a whole.

             "Merger" has the meaning set forth in Section 2.1(a).

             "Merger  Sub"  shall  mean  a   wholly-owned   subsidiary  of  AMSC
established for the purpose of consummating the Merger with MAA.

             "Multiemployer  Plan"  shall  mean  each  Benefit  Plan  that  is a
multiemployer plan, as defined in Section 3(37) of ERISA.

             "NASD" has the meaning set forth in Section 2.7(a)(iv).

             "Non-FCC  Authorizations"  shall mean all  licenses,  certificates,
permits,  franchises,  or other authorizations (other than FCC Licenses) granted
to MAA, MAI or any of the Subsidiaries by Governmental Entities that are used in
or relate to the conduct of the business of MAA, MAI or any of the Subsidiaries,
including,  without limitation,  those from any state public service commission,
public utility commission or similar state agency.

             "Nonsolicitation Period" has the meaning set forth in Section 5.10.

             "Notice Period" has the meaning set forth in Section 7.5(b).

             "Other Subsidiaries" shall mean the Subsidiaries other than ARDIS.

             "Other Tax Costs" means liabilities,  costs and expenses (including
reasonable  expenses  of  investigation  and  reasonable   attorneys'  fees  and
expenses)  arising  out  of or  incidental  to  the  imposition,  assessment  or
assertion of Taxes;  provided,  however,  that  expenses for  investigation  and
attorneys'  fees incurred prior to the time the  indemnified  party notifies the
indemnifying party of its claim for  indemnification  shall not constitute Other
Tax Costs if the indemnifying  party acknowledges in writing within fifteen (15)
days of the time of such  notice  that it assumes  full and  complete  financial
responsibility for the issue or issues for which  indemnification is sought; and
further  provided,  that Other Tax Costs  shall not  include  any  expenses  for
investigation or attorney fees incurred subsequent to the notification  referred
to in the preceding clause of this definition  provided the  indemnifying  party
timely makes the written acknowledgment described in such clause and is actively
handling the matter with respect to which indemnification is acknowledged.

             "Permitted Lien" shall mean (a) tax Liens with respect to taxes not
yet due and payable;  or which are being  contested in good faith by appropriate
proceedings and for which appropriate reserves (as determined in accordance with
and to the extent  required by GAAP) have been  established  on the books of any
Subsidiary with respect thereto; (b) deposits or pledges made in connection with
or to secure payment of utilities or similar  services,  workers'  compensation,
unemployment  insurance,  old age pensions or other social security obligations;
(c) interests or title of a lessor under any lease, mechanics', materialmen's or
contractors'  Liens or any similar Lien or  restriction  for amounts not yet due
and  payable;  (d)  easements,  rights-of-way,  restrictions  and other  similar
charges and encumbrances not materially interfering with the ordinary conduct of
the business of the  Subsidiaries  or detracting from the value of the assets of
its Subsidiaries;  (e) other Liens, imperfections in title, charges,  easements,
restrictions and encumbrances;  which,  individually or in the aggregate, do not
detract from the value in any material respect, or materially interfere with the
present use of the property subject thereto or affected thereby.

             "Person" shall mean an individual, a corporation,  a partnership, a
limited  liability  company,  an  association,   a  trust  or  other  entity  or
organization,  including a government or political  subdivision  or an agency or
instrumentality thereof.

             "Purchaser" has the meaning set forth in the introductory paragraph
hereof.

             "Real Property" has the meaning set forth in Section 3.20(a).

             "Realty  Rights"  shall mean those certain  easements,  privileges,
right-of-way agreements, surface use rights, servitudes, and other real property
interests  necessary for access to or which are ancillary or  appurtenant to the
use and  enjoyment  of other Real  Property or the  operation of the business of
MAA, MAI or the Subsidiaries.

             "Reconciliation Adjustment in Favor  of Purchaser"  has the meaning
set forth in Section 2.4.

             "Reconciliation Adjustment in Favor of Seller" has  the meaning set
forth in Section 2.4.

             "Registration  Rights Agreement"  has  the  meaning  set  forth  in
Section 5.8.

             "Regulatory Approvals" has the meaning set forth in Section 5.5.

             "Required Consents" has the meaning set forth in Section 3.2(b).

             "Securities Act" shall mean the Securities Act of 1933, as amended.

             "Seller"  has the meaning  set forth in the  introductory paragraph
hereof.

             "Seller Group" shall mean any Affiliated  Group including Seller or
any successor thereof or, if such Affiliated Group shall cease to exist,  Seller
and any successors thereto.

             "Severance Package" has the meaning set forth in Section 5.14.

             "Shares" shall mean all of the MAA Shares and MAI Shares.

             "Short Taxable Year" shall mean any Taxable Year that either begins
or ends on the Closing Date or begins on the date immediately  after the Closing
Date, in either case by reason of the purchase and sale of the Shares.

             "Split  Period" means a taxable period that begins on or before the
Closing Date and ends after the Closing Date.

             "State"  means  any state of the  United  States  of  America,  the
District of Columbia, or a local jurisdiction thereof.

             "Subsidiaries" shall mean ARDIS, ARDIS Holding,  Radio Data Network
Holding  Corporation,  and  each  corporation,  limited  liability  company  and
partnership identified as such in Section 3.1 of the Disclosure Schedule.

             "Tax"  or  "Taxes"  shall  mean  all  taxes,  however  denominated,
including  any  interest,  penalties  or  additions  to tax or other  additional
amounts  that may become  payable in respect  thereof,  imposed by any  federal,
State, local or foreign government or any agency or political subdivision of any
such government,  which taxes shall include,  without limiting the generality of
the  foregoing,  all net or gross  income  taxes,  payroll  and  employee  taxes
(including  withholding,  payroll and  employment  taxes required to be withheld
with  respect to income  paid to  employees),  withholding  taxes,  unemployment
insurance  taxes,   social  security  (or  similar)  taxes,   disability  taxes,
registration  taxes, sales and use taxes,  excise taxes,  franchise taxes, gross
receipts  taxes,  occupation  taxes,  premium  taxes,  windfall  profits  taxes,
environmental  taxes (including taxes under Code Section 59A), real and personal
property taxes, ad valorem taxes, stamp taxes, value added taxes, alternative or
add-on minimum taxes, transfer taxes, profits taxes, licenses,  estimated taxes,
severance taxes,  duties (custom and others),  workers'  compensation taxes, and
other taxes, customs,  duties, fees, assessments,  charges or obligations of the
same or of a similar nature,  whether  arising  before,  on or after the Closing
Date.

             "Tax  Returns"  shall  mean  all  returns,  declarations,  reports,
estimates,  and information  statements and returns relating to Taxes, including
but not limited to, original returns and filings,  amended  returns,  claims for
refunds, and information returns, and any schedules or attachments to any of the
foregoing.

             "Taxable  Year"  shall mean any taxable  year or any other  taxable
period  (including  any Short Taxable Year) with respect to which any Tax may be
imposed under any applicable statute, rule or regulation.

             "Threshold  Amount" shall mean an amount  resulting from an adverse
effect on the financial  condition,  assets or results of operations of MAA, MAI
or any of the Subsidiaries exceeding $50,000.

             "UPS Contract" has the meaning set forth in Section 5.12.

             "Working  Capital  Schedule"  has  the meaning set forth in Section
2.4(a).

                 ARTICLE 2. MERGER, PURCHASE AND SALE OF SHARES.

             Section 2.1   Merger, Purchase and Sale of Shares.   On the Closing
                           -----------------------------------
Date, on the terms and subject to the conditions hereinafter set forth:

                     (a)  AMSC shall cause Merger Sub to be merged with and into
MAA (the "Merger")  such that (i) each issued and  outstanding  share of capital
stock of  Merger Sub prior to the Merger shall be converted  into one MAA Share,
and (ii) any MAA Shares  issued and  outstanding  prior to the Merger  shall  be
converted into the right to receive the MAA  Purchase  Price to be  delivered in
exchange  therefor, such  that following the Merger, MAA shall be a wholly-owned
subsidiary of AMSC. The certificate of incorporation of Merger Sub, as in effect
on  the  date of  the  Merger  shall be the certificate of incorporation of MAA.
Immediately  following  the Merger, AMSC shall transfer all of the MAA Shares to
Purchaser.

                      (b)  Seller shall sell, assign,  transfer  and  deliver to
Purchaser, and Purchaser shall purchase, all of the MAI Shares free and clear of
all  Liens,  subject to release by the Escrow Agent of the MAI Purchase Price to
Seller, pursuant to the terms of the Escrow Agreement.

             Section 2.2 MAI Purchase Price and MAA Purchase Price. The purchase
                         -----------------------------------------
prices to be paid by AMSC and  Purchaser  for the MAI  Shares and the MAA Shares
shall  be paid  on the  Closing  Date as  follows:  (A) for the MAI  Shares,  by
depositing  with  the  Escrow  Agent  Fifty  Million  Dollars  ($50,000,000)  in
immediately  available funds, subject to adjustment pursuant to Sections 2.3 and
2.4 below (the "MAI Purchase Price"), payable by the Escrow Agent to Seller upon
receipt  by the  parties of a Final  Order from the FCC with  respect to the FCC
Authorization;  and (B) with respect to the MAA Shares acquired  pursuant to the
terms of Section 2.1(a),  by AMSC delivering to Seller  6,549,217 shares of AMSC
Common Stock (the  "Consideration  Shares") having,  in the aggregate,  a Market
Value as of the date hereof of Fifty Million Dollars  ($50,000,000),  subject to
adjustment pursuant to Sections 2.3 and 2.4 below (the "MAA Purchase Price"), to
Seller;  provided,  however, that the total number of Consideration Shares shall
not exceed 19.95% of the total number of shares of AMSC Common Stock outstanding
as of the Closing Date (including the Consideration  Shares), and, in such case,
AMSC shall also  deliver to Seller,  AMSC  Warrants to  purchase  that number of
shares of AMSC Common  Stock equal to the  difference  between (i) the number of
Consideration Shares which would be delivered but for this proviso and (ii) that
number of shares  equal to 19.95% of the total  number of shares of AMSC  Common
Stock outstanding as of the Closing Date.

             Section 2.3 Purchase Price Adjustments.  The MAI Purchase Price and
                         --------------------------
the MAA Purchase Price shall each be decreased by 50% of the negative difference
between the Closing Working  Capital and  $7,300,000.  Seller shall estimate the
Closing  Working  Capital in good faith (the  "Estimated  Working  Capital") and
deliver  such  estimate to Buyer not less than five  Business  Days prior to the
Closing Date. At Closing,  (i) the cash payment of the MAI Purchase  Price shall
be  $50,000,000  minus 50% of the  negative  difference  between  the  Estimated
Working Capital and $7,300,000 (the "Closing Cash Payment"), and (ii) the shares
of AMSC Common Stock  delivered  in payment of the MAA  Purchase  Price shall be
6,549,217 minus such number of shares having,  in the aggregate,  a Market Value
as of the  date  hereof  equal to 50% of the  negative  difference  between  the
Estimated  Working  Capital and $7,300,000  (the "Closing Stock  Payment").  For
purposes of this Agreement,  the term "Closing  Working  Capital" shall mean the
lesser of $7,300,000 and the actual working  capital of ARDIS, on a consolidated
basis,  as of the Closing Date determined from the books and records of ARDIS in
accordance  with past  practice and, to the extent not  inconsistent  therewith,
GAAP;  provided,  however,  that in no event shall the  proceeds  referenced  in
Section  5.16  hereof be  included in the  calculation  of the  Closing  Working
Capital.

             Section 2.4  Post-Closing Purchase Price Adjustment.
                          --------------------------------------

                      (a)  Not  more  than  60 days after the Closing, Purchaser
shall  prepare and deliver to Seller a schedule (the "Working Capital Schedule")
showing (i) the calculation of the actual Closing Working Capital of ARDIS; (ii)
the amount, if any, by which the  Closing  Working Capital exceeds the Estimated
Working  Capital (a "Reconciliation  Adjustment in  Favor of Seller"); and (iii)
the  amount, if  any, by  which  the Estimated  Working Capital is less than the
Closing Working Capital (a "Reconciliation Adjustment in Favor of Purchaser").

                      (b)  The proposed actual Closing Working Capital shown  in
the  Working  Capital  Schedule  shall become final and binding upon the parties
unless, within 30 days of delivery of the Working Capital Schedule, Seller shall
notify  Purchaser  of  its  objection  thereto.  If within 30 days following the
receipt of  such  notice  by  Seller any of such differences shall not have been
resolved, such  unresolved  issues  shall be referred to a nationally recognized
firm  of  independent certified  public  accountants, mutually acceptable to the
parties, for resolution, whose opinion thereon and the resulting  actual Closing
Working Capital shall be final, binding and not subject to any appeal.  The fees
and expenses of  such public accounting firm shall be paid one-half by Purchaser
and one-half by Seller.

                      (c)  On the applicable date referred to in Section 2.4(d),
(i) if there is a Reconciliation  Adjustment in Favor of Seller, Purchaser shall
(x) pay to Seller a cash amount equal to 50% of the Reconciliation Adjustment in
Favor of Seller  and (y)  deliver to the Seller a  certificate  evidencing  such
number of shares of AMSC Common Stock having,  in  aggregate,  a Market Value on
the  Closing  Date  equal to 50% of the  Reconciliation  Adjustment  in Favor of
Seller; and (ii) if there is a Reconciliation  Adjustment in Favor of Purchaser,
Seller  shall  (i)  pay  to  Purchaser  a  cash  amount  equal  to  50%  of  the
Reconciliation Adjustment in Favor of Purchaser and (y) deliver to the Purchaser
a stock certificate endorsed in blank such number of shares of AMSC Common Stock
having,  in  aggregate,  a Market  Value on the Closing Date equal to 50% of the
Reconciliation Adjustment in Favor of Purchaser. Any such payment is hereinafter
referred to as a "Final  Payment."  In the event that the Escrow Agent holds any
cash at the time of the  Final  Payment,  such  payment  to the  Seller  or such
payment by the Seller, as applicable,  shall instead be made to or by the Escrow
Agent.  Notwithstanding the foregoing,  in the event that any issuance to Seller
of shares of AMSC Common Stock under this Section 2.4 would, when taken together
with the  issuance to Seller of shares of AMSC Common  Stock under  Section 2.2,
cause the  number of such  shares  issued to Seller in the  aggregate  to exceed
19.95% of the total number of shares of AMSC Common Stock  outstanding as of the
date of the proposed issuance of shares under this Section 2.4(c) (including the
shares to be so issued),  AMSC shall deliver to Seller AMSC Warrants to purchase
that number of shares of AMSC Common Stock equal to the  difference  between (i)
the number of total shares which would be delivered  pursuant to Section 2.2 and
this  Section 2.4 but for this  sentence and (ii) that number of shares equal to
19.95% of the total number of shares of AMSC Common Stock  outstanding as of the
Closing Date.

                      (d)  Any Final Payment shall be made as follows:   (i) the
cash portion of any Final Payment shall be made by wire transfer of  immediately
available  funds within 5 Business  Days after its  determination  in accordance
with this  Section  2.4, to an account  specified  by the party to receive  such
Final Payment;  and (ii) the portion of any Final Payment payable in AMSC Common
Stock shall be made by transferring the stock  certificate(s)  representing such
shares  (and,  if  applicable,  stock  powers  executed  in blank),  within five
Business Days after its  determination  in accordance  with this Section 2.4, to
the party to receive such Final Payment. All such shares shall be delivered free
and clear of any Liens.

             Section  2.5  Closing  Place,  Date and Time.  The  closing  of the
                           ------------------------------
purchase and sale of the Shares (the "Closing")  shall take place at the offices
of Arnold & Porter,  555 12th Street,  N.W.,  Washington,  D.C. 20004 or at such
other place as Seller and  Purchaser may agree,  upon the effective  date of the
FCC Authorization,  or if Seller and Purchaser otherwise agree, then the Closing
shall take place at such later time and date as may be  mutually  agreed upon in
writing by the Seller and Purchaser.  All  transactions  shall be deemed to take
effect  at close of  business,  local  time,  on the  effective  date of the FCC
Authorization  or such other  time and date as may be  mutually  agreed  upon by
Seller  and  Purchaser  (such  time and date or such  other  time and date being
referred to herein as the "Closing Date").

             Section 2.6  FCC Authorization and Final Order.
                          ---------------------------------

                      (a)  FCC Authorization. Upon grant of a consent by the FCC
                           -----------------
sufficient  to  authorize  transfer  of the  Shares to  Purchaser  and to permit
Purchaser to operate the  businesses  of ARDIS and the Other  Subsidiaries  (the
"FCC  Authorization"),  and  satisfaction  or  waiver  of  the  representations,
warranties  and  covenants  herein,  the  parties  shall hold the Closing on the
Closing Date;  provided,  however,  that in the event either Seller or Purchaser
obtains an opinion of legal counsel, in substance and in form, and from counsel,
reasonably  satisfactory  to the  other  party,  that  there  exists a  material
likelihood  that the FCC will issue an adverse  Final Order with  respect to the
FCC Authorization (an "Adverse Legal Opinion"), the Closing shall not take place
until receipt of a Final Order of the FCC.

                      (b)  Favorable  Final Order.  Upon  receipt by the parties
                           ----------------------
of a  Final  Order  from  the  FCC  granting  consent  with  respect  to the FCC
Authorization,  the MAI Purchase  Price shall be released by the Escrow Agent to
the Seller in accordance with the terms of the Escrow Agreement.


             Section 2.7 Deliveries at the Closing.
                         -------------------------

                      (a) At the Closing,  Purchaser  and AMSC shall deliver the
following:

                              (i)   to the Escrow Agent, the MAI  Purchase Price
in immediately available funds, pursuant to the terms of the Escrow Agreement;

                              (ii)  to   the  Seller, the  MAA  Purchase  Price,
represented  by one or more  certificates  evidencing  AMSC Common Stock and, if
applicable, AMSC Warrants;

                              (iii) to  Seller, certified  copies of resolutions
duly  adopted  by  AMSC  and  Purchaser  constituting  all  necessary  corporate
authorization  for the  consummation  by AMSC and Purchaser of the  transactions
contemplated by this Agreement;

                              (iv)  to  Seller,  certified   copies  of  meeting
minutes  and  resolutions duly  adopted by the shareholders of AMSC Common Stock
approving  the  transactions  contemplated herein, as and to the extent required
under the Rules of the National Association of Securities Dealers, Inc. ("NASD")
(the "AMSC Shareholder Approval");

                              (v)   to  Seller,  the  certificate  required  by 
Section 6.2(d);

                              (vi)  to  Seller,  certificates  of incumbency for
all  relevant  officers  or  directors  of  AMSC and  Purchaser  executing  this
Agreement and any other documents pursuant to this Agreement;

                              (vii) to Seller, an opinion or opinions of counsel
to  AMSC and  Purchaser in form and substance reasonably satisfactory, including
opinions  with  respect  to  the  due organization and good standing of AMSC and
Purchaser, due  authorization of  AMSC and  Purchaser  to consummate and perform
their respective obligations under the  Agreement and Collateral Agreements, and
the due authorization and valid issuance of the AMSC Common Stock to Seller;

                              (viii) to Seller, an executed  Registration Rights
Agreement; and

                              (ix) to Seller, such other documents, instruments,
certificates  and  writings as  reasonably  may be  requested by Seller at least
three Business Days prior to the Closing.

                      (b) At the Closing, Seller shall deliver the following:

                              (i)  to  the  Purchaser,  the  stock  certificates
representing  all of the  Shares,  endorsed  in  blank  or  accompanied  by duly
executed instruments of transfer;

                              (ii)  to  AMSC  and  Purchaser,  the  certificates
required by Section 6.1(d);

                              (iii)  to  AMSC and Purchaser, certified copies of
the  certificate of  incorporation  and  by-laws  or  comparable  organizational
documents of MAA, MAI and each of the Subsidiaries and evidence of good standing
of each in its respective jurisdiction of incorporation and in each jurisdiction
where each is qualified to transact business as a foreign corporation;

                              (iv) to  AMSC  and  Purchaser, the  written
resignations  effective as of the Closing Date of all  directors and officers of
MAA, MAI and each of the Subsidiaries;

                              (v)  to  AMSC  and  Purchaser, the  minute  books,
corporate seals and stock ledger, or analogous  documents,  of MAA, MAI and each
of the Subsidiaries together with certificates evidencing all of the outstanding
shares of stock, or other comparable evidence of ownership  interest,  issued by
each of the Subsidiaries;

                              (vi) to AMSC and Purchaser, an opinion or opinions
of counsel to Seller in form and substance  reasonably  satisfactory,  including
opinions with respect to the due organization and good standing of Seller,  MAA,
MAI and the Subsidiaries, due authorization of Seller, MAI and MAA to consummate
and perform their  respective  obligations  under the  Agreement and  Collateral
Agreements,  and the due  authorization and valid issuance of the MAA Shares and
MAI Shares to Seller;

                              (vii) to AMSC and Purchaser, such other documents,
instruments, certificates and writings as reasonably may be requested by AMSC or
Purchaser at least three Business Days prior to the Closing.

             Section 2.8  Deliveries Post-Closing.  Within  15  Business Days of
                          -----------------------
the Closing  Date,  Seller  shall  deliver to  Purchaser  the Closing  Financial
Statements.



                    ARTICLE 3. REPRESENTATIONS AND WARRANTIES
                               OF SELLER

             Seller hereby  represents  and warrants as follows to Purchaser and
AMSC:

             Section 3.1  Organization and Good Standing.
                          ------------------------------

                    (a)  MAA,   MAI  and  each  of  the  Subsidiaries  are  duly
organized,  validly  existing  and in good  standing  under  the  laws of  their
respective  jurisdictions  of  organization  and each has the full  corporate or
partnership power to conduct its business as presently  conducted and to own and
operate the assets and  properties  now owned and operated by it. Section 3.1(a)
of the Disclosure  Schedule sets forth the full name of each of the Subsidiaries
and the state of organization of MAA, MAI and each of the  Subsidiaries and each
other  jurisdiction  in which MAA,  MAI or the  Subsidiaries  is qualified to do
business.  Except as set forth in Section 3.1(a) of the Disclosure Schedule, MAA
and MAI and each of the  Subsidiaries is duly qualified to do business and is in
good standing in each  jurisdiction  in which  qualification  is required as set
forth in Section 3.1(a) of the Disclosure  Schedule except, in each case, to the
extent that the failure to be so qualified is not reasonably  expected to have a
Material Adverse Effect.

                    (b)  Neither  MAA nor MAI has any  subsidiaries  or owns any
shares of any  corporation  or has any ownership or other  investment  interest,
either of record, beneficially,  or equitably, in any association,  partnership,
joint  venture or other  legal  entity  other than the 50%  general  partnership
interest each of MAA and MAI owns in ARDIS  Holding.  ARDIS Holding does not own
any  subsidiaries  or own any  shares of any  corporation  and does not have any
ownership  or other  investment  interest,  either of record,  beneficially,  or
equitably, in any association,  partnership, joint venture or other legal entity
other than its  ownership  of all of the issued and  outstanding  stock of Radio
Data  Network  Holding  Corporation  and its  ownership of all of the issued and
outstanding  general  partnership  interest in ARDIS which is not owned by Radio
Data Network Holding  Corporation.  Radio Data Network Holding  Corporation does
not own any  subsidiaries or own any shares of any corporation and does not have
any ownership or other investment interest, either of record,  beneficially,  or
equitably, in any association,  partnership, joint venture or other legal entity
other  than  its  ownership  of  all  of  the  issued  and  outstanding  general
partnership  interest in ARDIS which is not owned by ARDIS  Holding.  ARDIS does
not own any  subsidiaries or own any shares of any corporation and does not have
any ownership or other investment interest, either of record,  beneficially,  or
equitably, in any association, partnership, joint venture or other legal entity.

                    (c)  Section  3.1(c) of the  Disclosure  Schedule  lists the
directors  and  officers of MAA,  MAI and each of the  Subsidiaries.  Seller has
caused to be delivered to Purchaser true and complete  copies of the certificate
of  incorporation  and  bylaws  of MAA and MAI,  the  comparable  organizational
documents  of each of the  Subsidiaries,  and, to the extent that they relate to
the period from January 1, 1995 to the date  hereof,  the records of meetings of
their respective stockholders, members or partners, as the case may be, board of
directors, managers and any committees of their respective board of directors or
managers,  and all of the stock  record  books for all  periods  of MAA and MAI.
Neither MAA, MAI nor any of the Subsidiaries is in default under or in violation
of any  provision of its  certificate  of  incorporation,  bylaws or  comparable
organizational documents.

             Section  3.2  Authority;   No  Required  Consents  or  Governmental
                           -----------------------------------------------------
Authorizations; No Breach of Statute or Contract; Enforceability.
- ----------------------------------------------------------------

                    (a)  Seller,  MAA and MAI each has the full power and lawful
authority to execute and deliver this  Agreement and all  Collateral  Agreements
related  hereto and to  consummate  and  perform the  transactions  contemplated
hereby in the  manner  herein  provided.  The  execution  and  delivery  of this
Agreement and all Collateral  Agreements  related hereto by Seller,  MAA and MAI
and the consummation and performance by Seller,  MAA and MAI of the transactions
contemplated  hereby in the manner  herein  provided  have been duly and validly
authorized by all necessary corporate action.

                    (b) Except as set forth in Section  3.2(b) of the Disclosure
Schedule (each such item being a "Required Consent"),  and except for approvals,
consents or  authorizations  of, or filings with or notices to any  governmental
agency or body or any other third party that may be required in connection  with
the  issuance of AMSC Common  Stock or AMSC  Warrants  as  contemplated  hereby,
neither the execution and delivery by Seller,  MAA and MAI of this  Agreement or
all Collateral Agreements related hereto nor the consummation and performance by
Seller, MAA and MAI of the transactions contemplated hereby in the manner herein
provided (i) requires the approval,  consent or authorization  of, or any filing
with or notice to, any federal,  state,  local or other  governmental  agency or
body  or  any  other  third   party,   other  than  (A)   approvals,   consents,
authorizations,  filings or notices of a character such that a failure to obtain
them  would,  reasonably  be  expected  to have a  Material  Adverse  Effect  or
otherwise hinder the consummation of the  transactions  contemplated  hereby and
(B)  approvals,  consents,  authorizations,  filings or notices  which have been
obtained,  made or given, or (ii) conflicts with or will result in an uncured or
unwaived breach or violation of any term or provision of,  constitutes a default
under  or will  cause  the  acceleration  of any  payments  pursuant  to (A) the
certificates of incorporation, charters or By-laws, or comparable organizational
documents of MAA, MAI or any of the Subsidiaries,  (B) any indenture,  mortgage,
deed  of  trust,  lease,  note or  note  agreement  or any  other  agreement  or
instrument to which Seller, MAA, MAI or any of the Subsidiaries is a party or by
which  Seller,  MAA,  MAI or any of the  Subsidiaries  or any of their assets or
properties is bound, (C) any governmental  license,  franchise,  permit or other
authorization  held by Seller,  MAA, MAI or any of the  Subsidiaries  or (D) any
law, judgment, order, writ, injunction, decree, award, rule or regulation of any
court,  arbitrator or governmental agency or body applicable to Seller, MAA, MAI
or any of the Subsidiaries the breach or violation of which would,  singly or in
the  aggregate,  reasonably  be  expected to have a Material  Adverse  Effect or
otherwise prevent the consummation of the transactions contemplated hereby.

                    (c)  This   Agreement   constitutes,   and  all   Collateral

Agreements  related  hereto will be, when  executed and  delivered by Purchaser,
assuming the  enforceability  of this Agreement and such  Collateral  Agreements
upon Purchaser,  valid and binding  obligations of Seller, MAA and MAI, and will
be  enforceable  against  Seller,  MAA and MAI in  accordance  with their terms,
subject to applicable bankruptcy,  insolvency,  moratorium or other similar laws
affecting the rights of creditors generally.

             Section 3.3  Ownership of Shares.  The Shares are  owned  by Seller
                          -------------------
beneficially and of record, free and clear of all Liens.


             Section 3.4  Capitalization of MAA, MAI and the  Subsidiaries.  The
                          ------------------------------------------------
authorized  capital stock of MAA consists of 1,000 shares of Common Stock, 1,000
of  which  shares  are  issued  and are  outstanding  on the  date  hereof.  The
authorized  capital stock of MAI consists of 1,000 shares of Common Stock, 1,000
of which shares are issued and are  outstanding  on the date hereof.  All of the
Shares have been duly authorized,  are validly issued and  outstanding,  and are
fully paid and nonassessable. They are owned beneficially and of record as shown
in Section 3.4 of the Disclosure  Schedule.  There are no preemptive rights with
respect  to any of the  Shares.  The  authorized  capital  stock  of each of the
corporate Subsidiaries and the ownership of each Subsidiary's respective capital
interests,  are  as  shown  in  Section  3.4  of the  Disclosure  Schedule.  The
percentage ownership interests in each of the non-corporate  Subsidiaries are as
shown  in  Section  3.4  of the  Disclosure  Schedule.  All  of the  outstanding
ownership  interests  of the  Subsidiaries  have been duly  authorized,  validly
issued and are fully paid and nonassessable. There are no preemptive rights with
respect to any such ownership  interests.  Except as shown in Section 3.4 of the
Disclosure Schedule, each of MAA and MAI owns their respective interests in each
Subsidiary  beneficially and of record free and clear of all Liens. There are no
outstanding   agreements,    subscriptions,   options,   warrants,   convertible
securities,  calls,  commitments or rights of any kind (contingent or otherwise)
pertaining  to the issuance or purchase of any  securities of MAA, MAI or any of
the Subsidiaries.

             Section  3.5  Corporate  Records.  Purchaser  and  AMSC  have  been
                           ------------------
provided with current,  correct and complete copies of all charter  documents or
partnership  agreements,  as the case may be, of MAA, MAI and the  Subsidiaries,
respectively,  including all amendments  thereto and restatements  thereof.  The
stock record books,  or comparable  ownership  record books,  of MAA, MAI and of
each of the Subsidiaries,  respectively,  are also current, correct and complete
and reflects the issuance of all of the Shares to Seller.  All existing  minutes
of meetings and resolutions of MAA, MAI and the Subsidiaries  have been provided
to Purchaser  and AMSC and are correct,  and there have been no other actions or
proceedings  of  MAA's,  MAI's  or any  Subsidiary's  shareholders,  members  or
partners,  as the case may be, or boards of  directors,  managers or  committees
thereof of a nature which would have to be disclosed  under this  Agreement that
has not been so disclosed.


             Section 3.6  Employee Benefit Plans.
                          ----------------------

                      (a)  Section 3.6(a) of  the Disclosure Schedule contains a
true  and  complete  list  of the  Benefit  Plans.  Neither  MAA,  MAI,  nor any
Subsidiary has any formal plan or commitment, whether legally binding or not, to
create any  additional  plan or modify or change any existing  Benefit Plan that
would affect any employee or director or former  employee or former  director of
MAA, MAI or any Subsidiary.

                         (b) With respect to each of the Benefit  Plans,  Seller
has  heretofore  delivered  to AMSC  true  and  complete  copies  of each of the
following  documents:  (i) the Benefit Plan and related documents (including all
amendments  thereto);  (ii)  the  two  most  recent  annual  reports,  financial
statements,  and actuarial  reports,  if any; (iii) the most recent summary plan
description,  together  with each  summary of material  modifications,  required
under  ERISA with  respect  to such  Benefit  Plan,  and all  material  employee
communications  relating  to  such  Benefit  Plan;  and  (iv)  the  most  recent
determination  letter  received  from the IRS with  respect to each Benefit Plan
that is intended to be qualified under the Code and all material  communications
to or from the IRS or any other governmental or regulatory authority relating to
each Benefit Plan.

                         (c) No  liability  under  Title  IV of  ERISA  has been
incurred by ARDIS or any ERISA  Affiliate  that has not been  satisfied in full,
and no  condition  exists  that  presents  a  material  risk to MAA,  MAI or any
Subsidiary of incurring a liability under such Title.  None of the Benefit Plans
is subject to Title IV of ERISA.

                         (d) Neither MAA, MAI nor any Subsidiary, nor any of the
Benefit  Plans,   nor  any  trust  created   thereunder,   nor  any  trustee  or
administrator  thereof  has  engaged in a  prohibited  transaction  (within  the
meaning of Section 406 of ERISA and Section 4975 of the Code) in connection with
which MAA, MAI, or any Subsidiary  could incur,  either  directly or indirectly,
liability for either a civil penalty assessed  pursuant to Section 409 or 502(i)
of ERISA or a tax imposed  pursuant  to Section  4975 or 4976 of the Code or any
other liability or cost.

                         (e)  Full  payment  has been  made,  or will be made in
accordance with Section  404(a)(6) of the Code, of all amounts that ARDIS or any
ERISA  Affiliate  is required to pay under  Section 412 of the Code or under the
terms of the Benefit Plans,  and all amounts that have not been paid by MAA, MAI
or any  Subsidiary  under the Benefit  Plans are  properly  accrued  through the
Closing Date and recorded on the Closing Financial Statements.

                         (f) None of the Benefit Plans is a Multiemployer  Plan,
a "multiple  employer  welfare  arrangement," as such term is defined in Section
3(40) of ERISA,  or a single  employer  plan  that has two or more  contributing
sponsors, at least two of whom are not under common control,  within the meaning
of Section 4063(a) of ERISA.

                         (g) Each of the  Benefit  Plans that is  intended to be
"qualified"  within the meaning of Section  401(a) of the Code is so  qualified,
and a  determination  letter  to that  effect  has been  issued  by the IRS with
respect to each such Benefit Plan. Each of the Benefit Plans that is intended to
satisfy the  requirements of Section 125 or 501(c)(9) of the Code satisfies such
requirements.  Each of the Benefit Plans has been operated and  administered  in
all  material  respects  in  accordance  with its  terms  and  applicable  laws,
including but not limited to ERISA and the Code.

                         (h) There are no actions,  suits or claims pending, or,
to the  knowledge  of Sellers,  threatened  or  anticipated  (other than routine
claims for benefits) against any Benefit Plan, the assets of any Benefit Plan or
against ARDIS or any ERISA Affiliate with respect to any Benefit Plan.  There is
no judgment, decree, injunction,  rule or order of any court, governmental body,
commission,  agency or arbitrator outstanding against or in favor of any Benefit
Plan or any fiduciary thereof (other than rules of general applicability). There
are no pending or threatened audits or investigations by any governmental  body,
commission or agency involving any Benefit Plan.

                         (i)  No  Benefit  Plan  provides  benefits,   including
without  limitation  death or medical  benefits  (whether or not insured),  with
respect to current or former  employees or directors  after  retirement or other
termination of service (other than (i) coverage mandated by applicable law, (ii)
death benefit or retirement  benefits under any "employee pension plan," as that
term is defined in Section 3(2) of ERISA, (iii) deferred  compensation  benefits
accrued as  liabilities  on the ARDIS Balance Sheet or (iv)  benefits,  the full
cost of which is borne by the current or former  employee  or  director  (or his
beneficiary)).

                         (j)  None  of the  assets  of  the  Benefit  Plans  (i)
constitute  employer real property or employer securities (within the meaning of
Section  407(d) of ERISA),  or (ii) are  invested in any  property,  security or
other ownership interest that is not publicly traded.

                         (k) The consummation of the  transactions  contemplated
by this  Agreement  will not (i)  entitle  any  current  or former  employee  or
director  of  MAA,  MAI,  or  any  Subsidiary  to  severance  pay,  unemployment
compensation or any similar  payment,  or (ii) accelerate the time of payment or
vesting,  or increase the amount, of any compensation due to any such current or
former employee or director,  or (iii) renew or extend the term of any agreement
regarding  compensation for any such current or former employee or director.  On
and  after  January  1,  1997,  except  as set  forth on  Section  3.6(k) of the
Disclosure  Schedule no employee  or former  employee of MAA,  MAI or any of the
Subsidiaries has become covered by, or a participant in, the ARDIS  Supplemental
Executive Retirement Plan, Long-Term Incentive Plan, or Retention Bonus Plan.

               Section  3.7  Broker's  or  Finder's  Fees.  No  agent,   broker,
                             ----------------------------
investment  banker,  person  or firm  acting  on  behalf  of Seller or under its
authority is or will be  entitled,  directly or  indirectly,  to collect from or
otherwise hold Purchaser,  AMSC, MAA, MAI or any of the Subsidiaries  liable for
any  broker's  or  finder's  fee or  any  other  commission  or  similar  fee in
connection with any of the transactions contemplated herein.


             Section 3.8 Financial Statements.  (a) The Financial Statements are
                         --------------------
complete copies of all of which have been delivered to Purchaser, present fairly
in all material  respects the financial  position and assets and  liabilities of
ARDIS Holding as of their  respective  dates,  and the results of its operations
for the fiscal periods then ended,  in conformity  with GAAP provided,  however,
that the Interim Financial Statements are subject to normal, year-end adjustment
and lack  footnotes  and other  presentation  items.  On the Closing  Date,  the
consolidated balance sheet of ARDIS Holding as of December 31, 1997, the related
consolidated  statements  of income and retained  earnings and notes thereto for
the  12-month  period then ended,  examined  by KPMG Peat  Marwick,  independent
certified public accountants, a complete copy of which shall have been delivered
to Purchaser  prior to the Closing Date,  shall  present  fairly in all material
respects the financial  position and assets and  liabilities of ARDIS Holding as
of December 31, 1997,  and the results of its  operations  for the fiscal period
then ended,  in conformity  with GAAP.  All  references in this Agreement to the
"ARDIS  Balance  Sheet Date"  shall be deemed to refer to  September  30,  1997;
provided,  however, that on the Closing Date all references in this Agreement to
the "ARDIS Balance Sheet Date" shall be deemed to refer to the audited  December
31, 1997.

                    (b) Neither Seller nor any other Person regularly  compiles,
maintains or prepares  financial  statements  for MAI or MAA.  Each of MAA, MAI,
ARDIS Holding and Radio Data Network Holding  Corporation  undertakes no regular
financial  or  business  activities  and has no material  assets  other than its
ownership interests in the Subsidiaries.

          Section 3.9 Accounts  Receivable.  All accounts receivable included in
                      --------------------
the calculation of the actual Closing  Working  Capital  pursuant to Section 2.4
will have arisen only in the ordinary  course of business,  consistent with past
practice, and will not be subject to defenses, set-offs or counterclaims. All of
such accounts receivable are generally due within 30 days after being accrued on
the books of ARDIS. The allowance for such doubtful  accounts in the calculation
of the  actual  Closing  Working  Capital  pursuant  to  Section  2.4  has  been
determined in accordance with GAAP.

          Section 3.10 Absence of Undisclosed  Liabilities.  Except as disclosed
                       -----------------------------------
in Section 3.10 of the Disclosure Schedule or elsewhere in this Agreement or the
Disclosure  Schedule,  neither MAA nor MAI has any  liabilities or  obligations,
either  accrued,  absolute,  contingent  or  otherwise.  Except as  disclosed in
Section 3.10 of the  Disclosure  Schedule or elsewhere in this  Agreement or the
Disclosure   Schedule,   none  of  the   Subsidiaries  has  any  liabilities  or
obligations, either accrued, absolute, contingent or otherwise, except:

                    (a) those  liabilities or obligations set forth on the ARDIS
Balance Sheet and not heretofore paid or discharged;

                    (b)  liabilities  arising in the ordinary course of business
under any agreement,  contract, commitment, lease or plan specifically disclosed
on the Disclosure  Schedule or not required to be disclosed  because of the term
or amount involved or otherwise; and

                    (c) those liabilities or obligations incurred,  consistently
with past business practice, in or as a result of the normal and ordinary course
of business since the ARDIS Balance Sheet Date.

             For purposes of this Section, the term "liabilities" shall include,
without limitation, any direct or indirect indebtedness,  guaranty, endorsement,
claim, loss, damage,  deficiency,  cost, expense,  obligation or responsibility,
known  or  unknown,  fixed  or  unfixed,  choate  or  inchoate,   liquidated  or
unliquidated, secured or unsecured.

             Section 3.11   Existing  Condition.  Except as disclosed in Section
                            -------------------
3.11 of the Disclosure Schedule,  since December 31, 1996 in the case of MAA and
MAI and since  the ARDIS  Balance  Sheet  Date in the case of the  Subsidiaries,
neither MAA, MAI nor any of the Subsidiaries has:

                    (a)  declared,  set  aside or paid any  dividend  or made or
agreed to make any other  distribution  or payment  in  respect  of its  capital
shares or  redeemed,  purchased  or  otherwise  acquired  or  agreed to  redeem,
purchase or acquire any of its capital shares;

                    (b)  incurred  any   liabilities,   other  than  liabilities
incurred in the ordinary course of business  consistent  with past practice,  or
discharged or satisfied any lien or encumbrance, or paid any liabilities,  other
than in the ordinary course of business consistent with past practice, or failed
to pay or  discharge  when due any  liabilities  of which the  failure to pay or
discharge  has caused or is  reasonably  expected  to cause a  Material  Adverse
Effect;

                    (c)  sold,  assigned  or  transferred  any of its  assets or
properties  except in the  ordinary  course  of  business  consistent  with past
practice;

                    (d)   created,   incurred,   assumed   or   guaranteed   any
indebtedness for money borrowed, or mortgaged, pledged or subjected to any Lien,
conditional  sales contract or other encumbrance of any nature whatsoever any of
its assets or properties, other than Permitted Liens;

                    (e)  made  or  suffered  any   material   amendment  or  any
termination of any material agreement,  contract,  commitment,  lease or plan to
which it is a party or by which it is bound,  or  cancelled,  modified or waived
any debts or claims held by it,  other than in the  ordinary  course of business
consistent with past practice;

                    (f) suffered any damage, destruction or loss, whether or not
covered by  insurance  which has had a Material  Adverse  Effect or suffered any
repeated, recurring or prolonged shortage, cessation or interruption of supplies
or utility services required to conduct its business and operations;

                    (g) suffered any Material  Adverse  Change after taking into
account all disclosures set forth on the Disclosure Schedule;

                    (h)  received  notice  or has  knowledge  of any  actual  or
threatened labor, union organizing effort, strike or other occurrence,  event or
condition or any similar character which has had or could reasonably be expected
to have a Material Adverse Effect;

                    (i)  received  any notice or has any  knowledge of any basis
for  assertions  of  liability,   claims,  causes  of  action,  charges,  suits,
complaints,    administrative   proceedings,    government   investigations   or
proceedings,  arbitrations or other  proceedings  pending or threatened  against
MAA, MAI or any of the  Subsidiaries  relating to any current or former employee
or director of MAA, MAI or any of the  Subsidiaries,  or any  federal,  state or
local laws and  regulations  thereunder or the common law relating to employment
or employment practices of MAA, MAI or any of the Subsidiaries;

                    (j) made any  capital  expenditure  or capital  addition  or
betterment  except such as may be involved in ordinary  repair,  maintenance and
replacement of its assets;

                    (k) increased the salaries or other compensation of, or made
any advance (excluding advances for ordinary and necessary business expenses) or
loan to, any of its shareholders, partners, directors, officers or employees, or
made any increase  in, or any  addition  to, other  benefits to which any of its
shareholders,  partners,  directors, officers or employees may be entitled other
than in the ordinary cause of business;

                    (l) changed any of the accounting  principles followed by it
or the methods of applying such principles; or

                    (m) entered into any transaction  other than as contemplated
by this  Agreement or in the ordinary  course of business  consistent  with past
practice.

             Section 3.12 Title to Properties; Leasehold Interests. MAA, MAI and
                          ----------------------------------------
each of the  Subsidiaries  has valid title to all of its  properties and assets,
real,  personal  and  mixed,  including  all  Real  Property,  and  all of  such
properties and assets free and clear of all Liens,  except  Permitted  Liens and
those items  disclosed in Section 3.12 of the Disclosure  Schedule.  All leases,
licenses,  permits  and  authorizations  in any  manner  related  to the real or
personal  properties used by MAA, MAI or any of the  Subsidiaries  and all other
instruments,  documents and agreements  pursuant to which MAA, MAI or any of the
Subsidiaries has obtained the right to use any real or personal  property are in
good standing,  valid and effective in accordance with their  respective  terms,
and there is not under any of such  instruments,  documents  or  agreements  any
existing  default or event  which with notice or lapse of time,  or both,  would
constitute a default and in respect of which MAA, MAI or any of the Subsidiaries
has not taken adequate steps to prevent a default from occurring.

               Section  3.13  Condition  of  Tangible  Assets.  All  buildings,
                              -------------------------------
structures,   facilities,   automobiles,   trucks,  other  vehicles,  machinery,
equipment  and other  material  items of  tangible  personal  property  owned or
operated by MAA,  MAI or any of the  Subsidiaries  are usable in the regular and
ordinary course of business of MAA, MAI or the  Subsidiaries  and conform in all
material  respects  to  all  applicable  laws,  ordinances,   codes,  rules  and
regulations relating to their construction,  use and operation.  The failure, if
any, of such  buildings,  structures,  facilities,  automobiles,  trucks,  other
vehicles,  machinery,  equipment and other material  items of tangible  personal
property  to  be in  good  operating  condition,  subject  to  normal  wear  and
maintenance, is not reasonably expected to have a Material Adverse Effect.

             Section  3.14  Books of  Account.  The  books  of  account of ARDIS
                            -----------------
reflect  all  of its  items  of  income  and  expense,  and  all of its  assets,
liabilities and accruals  required to be reflected  therein,  in accordance with
GAAP.

             Section  3.15  Litigation.  Except as listed in Section 3.15 of the
                            ---------- 
Disclosure  Schedule,  no  litigation,   arbitration,   investigation  or  other
proceeding  of or before any court,  arbitrator  or  governmental  or regulatory
official,  body  or  authority  is  pending  or,  to the  knowledge  of  Seller,
threatened  against  MAA,  MAI  or  any of the  Subsidiaries  or  their  assets,
properties or business,  or the  transactions  contemplated  by this  Agreement.
Other than as listed in Section 3.15 of the  Disclosure  Schedule,  neither MAA,
MAI nor any of the  Subsidiaries  is a party to or subject to the  provisions of
any judgment, order, writ, injunction,  decree or award of any court, arbitrator
or governmental or regulatory official, body or authority.

             Section  3.16  Compliance  with  Law.  MAA,  MAI  and  each  of the
                            ---------------------
Subsidiaries  has  complied  with each,  and is not in  violation  of any,  law,
ordinance,  or governmental  rule or regulation to which they or their business,
operations,  assets or properties are subject and has not failed to obtain or to
adhere to the requirements of any license,  permit or authorization necessary to
the  ownership of its assets and  properties  or to the conduct of its business,
which  noncompliance,  violation  or  failure  to  obtain  or  adhere  to  would
reasonably be expected to have a Material Adverse Effect.  Neither MAA, MAI, any
of the  Subsidiaries nor any officer,  employee or agent thereof,  or consultant
thereto has unlawfully offered,  paid, or agreed to pay, directly or indirectly,
any money or anything of value to, or for the benefit of, any  individual who is
or was a  candidate  for  public  office,  or an  official  or  employee  of any
governmental  or  regulatory  body or authority or an officer or employee of any
client, customer or supplier of MAA, MAI or any of the Subsidiaries.

             Section 3.17 Environmental Matters.  Section 3.17 of the Disclosure
                          ---------------------
Schedule  contains an accurate and  complete  description  of all  Environmental
Liabilities,  investigations, actions, proceedings of whatsoever nature, whether
pending or to Seller's  knowledge  threatened,  involving MAA, MAI or any of the
Subsidiaries or their respective  properties,  assets,  operations or businesses
arising under any Environmental  Law. Except as specified in Section 3.17 of the
Disclosure  Schedule:  (a) the  business of MAA, MAI and the  Subsidiaries,  the
methods and means  employed by MAA, MAI and the  Subsidiaries  in the  operation
thereof (including all operations and conditions at or in the properties of MAA,
MAI and the  Subsidiaries),  and the assets owned,  leased,  held or operated by
MAA,  MAI and  the  Subsidiaries,  comply  in all  material  respects  with  all
Environmental  Laws; (b) MAA, MAI and the Subsidiaries have obtained all permits
under Environmental Laws necessary to their operations, and all such permits are
in good standing and MAA, MAI and the  Subsidiaries  are in compliance  with all
material terms and conditions of such permits;  and (c) neither MAA, MAI nor any
of the  Subsidiaries  has received (i) any written claim or notice of violation,
lien, complaint, suit, order or other written claim or notice to the effect that
it is or may be  liable  to any  Person  as a  result  of (A) the  environmental
condition of any of their  respective  properties or any other property,  or (B)
the release or threatened release of any Hazardous Materials, or (ii) any letter
or request for information under Section 104 of CERCLA or comparable state laws,
and  to  Seller's  knowledge,  none  of  the  operations  of  MAA,  MAI  or  the
Subsidiaries  are the subject of any federal or state  investigation  evaluating
whether  any  remedial  action is needed to respond  to a release or  threatened
release,  of any  Hazardous  Material  at  MAA's,  MAI's  or  the  Subsidiaries'
properties or at any other location, including any location to which MAA, MAI or
the Subsidiaries have transported,  or arranged for the  transportation  of, any
Hazardous Materials.

             Section 3.18  Insurance.  Section 3.18 of the  Disclosure  Schedule
                           ---------
contains a correct and  complete  list of all  insurance  policies or binders of
insurance  held by or on behalf  ARDIS  relating  to its  business or any of its
assets or properties  (specifying the insurer,  the amount of the coverage,  the
type of insurance,  the risks insured and any pending  claims  thereunder).  The
policies and binders  listed in Section 3.18 of the Disclosure  Schedule  hereto
are duly in force as of the date hereof. There is no default with respect to any
material  provision  contained in any such policy or binder,  nor has there been
any  failure to give any notice or present  any claim  under any such  policy or
binder in a timely fashion or in the manner or detail  required by the policy or
binder.  There  are no  outstanding  unpaid  premiums  or  claims.  No notice of
cancellation  or nonrenewal with respect to, or disallowance of any claim under,
any  such  policy  or  binder  has  been  received  by  MAA,  MAI  or any of the
Subsidiaries.  Section 3.18 of the Disclosure  Schedule also contains a true and
complete  description  of all  outstanding  bonds and other surety  arrangements
issued or entered into in  connection  with the business and  operations of MAA,
MAI or any of the Subsidiaries.

             Section  3.19   Contracts  and  Commitments.   Except as listed and
                             ---------------------------
described in Section 3.19 of the Disclosure  Schedule,  neither MAA, MAI nor any
of the Subsidiaries is a party to any written or oral:

                    (a)  agreement,  contract or commitment  with any present or
former  shareholder,  director,  officer,  employee  or  consultant  or for  the
employment of any person,  including any  consultant  pursuant to which payments
thereunder are  obligations of MAA, MAI or any Subsidiary  which are not payable
by Seller;

                    (b) agreement,  contract, commitment or arrangement with any
labor union or other representative of employees;

                    (c) agreement,  contract, commitment for the future purchase
of, or payment for, supplies or products,  or for the performance of services by
a third party, involving in any one case $50,000 or more;

                    (d)  agreement,  contract,  commitment  to  sell  or  supply
products or to perform services, having with respect to revenues to be delivered
or potential  liabilities  reasonably to be incurred in any one case $100,000 or
more on an annual basis;

                    (e) agreement,  contract, commitment not otherwise listed on
the Disclosure  Schedule and continuing over a period of more than twelve months
from the date hereof or exceeding $100,000 in value;

                    (f) lease for office  space under  which MAA,  MAI or any of
the Subsidiaries is either the lessor or lessee;

                    (g) agreement,  contract or commitment for any charitable or
political contribution;

                    (h)  agreement,  contract,  or  commitment  for any  capital
expenditure in excess of $100,000;

                    (i)   agreement,   contract   or   commitment   limiting  or
restraining  it from  engaging or  competing  in any lines of business  with any
person,  and  neither  Seller nor any officer or employee of ARDIS is subject to
any such  agreement,  contract  or  commitment  which would  prohibit  them from
continuing their employment in the same capacity as that in which they currently
perform services for ARDIS; or

                    (j) agreement, contract or commitment by or between MAA, MAI
or any of the  Subsidiaries  and Seller or any  Affiliate of Seller  (other than
MAA, MAI or any of the Subsidiaries).

             Except  as may be  disclosed  in  Section  3.19  of the  Disclosure
Schedule, to Seller's knowledge, each of the agreements, contracts, commitments,
leases  and  other  instruments,   documents  and  undertakings  listed  on  the
Disclosure  Schedule  is in full  force  and  effect;  Seller,  MAI,  MAA or the
Subsidiaries  which are parties  thereto,  and, to the knowledge of Seller,  all
other parties thereto are in compliance with the provisions  thereof and are not
in  default  in the  performance,  observance  or  fulfillment  of any  material
obligation,  covenant or condition  contained  therein and no event has occurred
which with or  without  the  giving of notice or lapse of time,  or both,  would
constitute  a default  thereunder  by MAI,  MAA or the  Subsidiaries  or, to the
knowledge  of  Seller,  by any  other  parties  thereto;  and,  except as may be
disclosed  on the  Disclosure  Schedule,  to the  knowledge  of Seller,  no such
agreement,  contract,  commitment,  lease  or  other  instrument,   document  or
undertaking,  in the  reasonable  opinion of Seller,  contains  any  contractual
requirement  with  which  there  is  a  reasonable   likelihood  MAA,  MAI,  the
Subsidiaries or any other party thereto will be unable to comply,  assuming that
MAA, MAI and the  Subsidiaries  continue in all  material  respects to be in the
same financial condition as they are as of the date hereof.

             Section  3.20   Additional   Information.    Section  3.20  of  the
                             ------------------------
Disclosure  Schedule,  to the extent not described  elsewhere in the  Disclosure
Schedule, contains accurate lists and summary descriptions of the following:

                    (a)  all  real  property  and  interests  in  real  property
(including Realty Rights) owned,  leased or otherwise held by MAA, MAI or any of
the Subsidiaries other than antennae and transmitter sites (collectively,  "Real
Property")  as of the date  hereof  which  listing  shall be  updated  as of the
Closing,  specifying  which are owned,  which are  leased  and which  constitute
Realty  Rights  and,  (i) with  respect  to the  owned  Real  Property,  if any,
specifying  its cost or  original  value and the net book  value as of the ARDIS
Balance  Sheet  Date and (ii) with  respect  to leased  or  otherwise  held Real
Property, the current term of ownership and rental rate applicable thereto;

                    (b) all machinery,  vehicles and equipment owned by MAA, MAI
or the Subsidiaries  which has an original cost of at least $50,000,  specifying
the cost thereof and the net book value  thereof as of the ARDIS  Balance  Sheet
Date;

                    (c) the names of all present  officers and directors of MAA,
MAI and each of the Subsidiaries;

                    (d)  the  names  and  addresses  of  every  bank  and  other
financial institution in which MAA, MAI or any of the Subsidiaries  maintains an
account (whether checking, savings or otherwise),  lock box or safe deposit box,
and the account  numbers and names of persons having signing  authority or other
access thereto;

                    (e) the names of all persons  authorized  to borrow money or
incur  indebtedness  for  borrowed  money on  behalf  of MAA,  MAI or any of the
Subsidiaries or obligate MAA, MAI or any of the Subsidiaries as a guarantor with
respect to indebtedness for borrowed money; and

                    (f) the names of all persons holding powers of attorney from
MAA,  MAI or any  of the  Subsidiaries  and a  summary  statement  of the  terms
thereof.

             Section 3.21  Intellectual Property.
                           ---------------------

                    (a) Section  3.21(a) of the Disclosure  Schedule  accurately
lists  all  of  the  Intellectual  Property  owned  by  MAA,  MAI  or any of the
Subsidiaries  which has been duly registered with, filed in or issued by, as the
case may be, the United  States  Patent and  Trademark  Office,  U.S.  Copyright
Office, or any similar  governmental agency in any foreign country, as indicated
in Section 3.21(a) of the Disclosure  Schedule.  Unless  otherwise  indicated in
such Section 3.21(a),  MAA, MAI or the Subsidiaries own the entire right,  title
and  interest  in  and  to  such  Intellectual   Property  (including,   without
limitation,  the  exclusive  right to use and license  the same).  Except as set
forth in Section 3.21(a) of the Disclosure Schedule, neither MAA, MAI nor any of
the  Subsidiaries  has granted,  any license or other right with respect to such
Intellectual  Property  which does or which  will,  subsequent  to the  Closing,
permit or enable any Person other than MAA, MAI or the  Subsidiaries to use such
Intellectual Property. To the knowledge of Seller, no such Intellectual Property
or MAA's,  MAI's or the  Subsidiaries'  use  thereof,  infringes or violates the
rights of third  parties.  To the  knowledge of Seller,  MAA and MAI,  except as
indicated in Section 3.21(a) of the Disclosure Schedule, no Person is infringing
upon  any  of  the  Intellectual  Property  listed  in  Section  3.21(a)  of the
Disclosure Schedule.

                    (b) Set forth in Section 3.21(b) of the Disclosure  Schedule
is a list of all Intellectual  Property owned by third parties which is licensed
to, or otherwise  used in the business of, MAA, MAI or any of the  Subsidiaries.
All such Intellectual Property is licensed pursuant to valid written agreements.
MAA's, MAI's or the Subsidiaries use of such listed Intellectual  Property owned
by Seller or any of its  Affiliates  (other than MAA, MAI or the  Subsidiaries),
does not  infringe  or violate the rights of third  parties.  Except only as set
forth in Section  3.21(b)  of the  Disclosure  Schedule,  there is no pending or
threatened  written  claim  against MAA, MAI or any of the  Subsidiaries,  or to
Seller's  knowledge,  the  licensors  of  such  licensed  Intellectual  Property
asserting that any of such licensed  Intellectual  Property,  or MAA's, MAI's or
the Subsidiaries' use thereof, infringes or violates the rights of third parties
or that MAA, MAI or any of the Subsidiaries is in breach of any such agreement.

                    (c)  To  the   knowledge   of  Seller,   MAA,  MAI  and  the
Subsidiaries  own or have the  right to use all  Intellectual  Property  used in
their  businesses  as  conducted on the date hereof.  Upon  consummation  of the
transactions  contemplated by this Agreement, MAA, MAI and the Subsidiaries will
be entitled to continue to use all Intellectual Property used in the business of
MAA, MAI or the  Subsidiaries  as it is used to conduct their business as of the
Closing  Date  without any  limitation,  impairment  or  alteration  thereof and
without the payment of any fees or license or other payments. Section 3.21(c) of
the Disclosure Schedule lists all written notices or claims received by MAA, MAI
or  any  of  the  Subsidiaries  which  claim  infringement  by  MAA,  MAI or the
Subsidiaries  of any  Intellectual  Property which is claimed to be owned by any
other person.  To the knowledge of Seller,  there is no basis for any such claim
listed in Section 3.21(c) of the Disclosure Schedule.

              Section  3.22 No  Third  Party  Options.  There  are  no  existing
                            -------------------------
agreements,  options, commitments or rights with, to or in any person to acquire
any of MAA, MAI or any of the Subsidiaries' assets or properties or any interest
therein,  except for this  Agreement  and those  contracts  entered  into in the
normal  course of business  consistent  with past practice for the sale of MAA's
MAI's or any Subsidiary's products or services.


             Section 3.23  Tariffs; FCC Licenses; Non-FCC Authorizations.
                           ---------------------------------------------

                    (a) Section  3.23(a) of the  Disclosure  Schedule lists each
tariff  applicable to MAA, MAI or any of the Subsidiaries as of the date hereof,
a true  and  correct  copy of each of  which  has  been or will be  provided  to
Purchaser.  Except as otherwise set forth in Section  3.23(a) of the  Disclosure
Schedule,  (i) such  tariffs  stand in full  force and  effect,  and there is no
outstanding notice of cancellation or termination or, to Seller's knowledge, any
threatened  cancellation  or termination in connection  therewith,  (ii) neither
MAA,  MAI nor  any of the  Subsidiaries  is  subject  to,  any  restrictions  or
conditions applicable to such tariffs that limit or would limit the operation of
its business  (other than  restrictions  or conditions  generally  applicable to
tariffs  of that  type).  Neither  MAA,  MAI nor any of the  Subsidiaries  is in
violation  under the terms and  conditions  of any of its  tariffs in any manner
which could  reasonably be expected to result in a Threshold Amount with respect
to MAA, MAI or any of the  Subsidiaries.  Except as set forth in Section 3.23(a)
of the Disclosure Schedule,  there are no applications by MAA, MAI or any of the
Subsidiaries or to Seller's knowledge,  complaints, filings, orders or petitions
by others or proceedings pending or threatened before the appropriate regulatory
authority  relating to the business or operations or regulatory  tariffs of MAA,
MAI or any of the Subsidiaries as of the date hereof.

                    (b) Section  3.23(b) of the  Disclosure  Schedule lists each
FCC License  held by MAA, MAI or any of the  Subsidiaries  as of the date hereof
which list shall be updated as of the  Closing  Date.  Except as  otherwise  set
forth  in  Section  3.23(b)  of  the  Disclosure  Schedule,  such  FCC  Licenses
constitute  all FCC Licenses  necessary  for the conduct of the business of MAA,
MAI and each of the  Subsidiaries as conducted and as anticipated as of the date
hereof to be  conducted  in the 12 month  period  following  the date hereof and
thereafter as contemplated in material  respects under the UPS Contract.  Except
as otherwise set forth in Section 3.23(b) of the Disclosure Schedule,  each such
FCC License is in full force and effect,  and there is no outstanding  notice of
cancellation   or  termination  or,  to  Seller's   knowledge,   any  threatened
cancellation or termination in connection  therewith.  None of such FCC Licenses
is  subject to any  restrictions  or  conditions  except as set forth on Section
3.23(b) of the Disclosure  Schedule that limit the operations of MAA, MAI or any
of the Subsidiaries (other than restrictions or conditions  generally applicable
to  licenses  of that  type).  Subject  to the  Communications  Act of 1934,  as
amended,  and the  regulations  thereunder,  the FCC  Licenses are free from all
security  interests,  liens,  claims, or encumbrances of any nature  whatsoever.
Except as set forth in Section 3.23(b) of the Disclosure Schedule,  there are no
applications by MAA, MAI or any of its Subsidiaries  or, to Seller's  knowledge,
complaints or petitions by others or  proceedings  pending or threatened  before
the FCC  relating  to the  business or FCC  Licenses  of MAA,  MAI or any of the
Subsidiaries  as of the date  hereof or which  could  reasonably  be expected to
result in a Threshold Amount with respect to MAA, MAI or any of the Subsidiaries
as of the Closing Date.

                    (c) Section  3.23(c) of the  Disclosure  Schedule  lists all
material  Non-FCC  Authorizations  necessary  for the conduct of the business of
MAA, MAI and each of the  Subsidiaries as of the date hereof which list shall be
updated as of the Closing Date. Except as otherwise set forth in Section 3.23(c)
of the Disclosure Schedule,  each such material Non-FCC Authorization is in full
force and  effect.  No event has  occurred  with  respect  to any such  material
Non-FCC  Authorization  which (i)  permits,  or after notice or lapse of time or
both would permit,  revocation or termination  thereof,  or (ii) would result in
any other impairment of the rights of the holder of such Non-FCC Authorization.

             Section 3.24  Officer and Employee Compensation.  Section 3.24 of 
                           ---------------------------------
the Disclosure  Schedule lists each officer and employee of MAA, MAI and each of
the  Subsidiaries  and  such  officer's  or  employee's   corresponding   annual
compensation  amount  payable by any of MAA,  MAI or any such  Subsidiary  as of
December 31, 1997.


             Section  3.25  Indebtedness.  Neither  MAA,  MAI  nor  any  of  the
                            ------------
Subsidiaries  is  subject  to any note,  debenture,  bond,  conditional  sale or
equipment trust agreement,  letter of credit agreement, loan agreement, or other
contract or commitment for the borrowing or lending of money (including, without
limitation, loans to or from officers,  directors,  shareholders, or any members
of their immediate families),  any non-vendor financing  arrangement with Seller
or any  Affiliate of Seller (other than the  Subsidiaries),  or any agreement or
arrangement  for a line of credit,  or guarantee,  pledge or  undertaking of the
indebtedness of any other Person.

             Section 3.26  Access; Sophistication; etc.
                           ----------------------------

                    (a)  Purchaser  and AMSC have  furnished to Seller copies of
their  respective  most recent  financial  statements  and Seller in agreeing to
accept the AMSC Common Stock has reviewed such  documents and has relied only on
(i)  the   statements   and   information   contained   therein   and  (ii)  the
representations, warranties, terms and conditions of this Agreement.

                    (b)  Seller  acknowledges  that  all  documents,  books  and
records  requested by Seller  pertaining  to  Purchaser  and AMSC have been made
available  for  inspection  by Seller and its agents and  representatives;  that
Seller and its agents and representatives  have had a reasonable  opportunity to
ask  questions  of and receive  answers from  Purchaser  and AMSC or officers or
employees  acting on  behalf  of  Purchaser  and AMSC  concerning  the terms and
conditions  of the AMSC Common Stock and the business and prospects of Purchaser
and  AMSC.  Seller  and its  respective  agents  and  representatives  have such
knowledge and experience in financial and business  matters as to enable them to
utilize  the  information   made  available  to  them  in  connection  with  the
transactions  contemplated hereby, to evaluate the merits and risks of accepting
the AMSC Common Stock and to make an informed  decision with respect thereto and
such an evaluation and informed decision have been made.

             Section 3.27  Investment  Representation.  Seller is acquiring  the
                           --------------------------
shares of AMSC Common  Stock to be received by Seller upon  consummation  of the
sale of Seller's Shares to Purchaser for its own account for investment only and
not with a view to making a  distribution  thereof  within  the  meaning  of the
Securities  Act of 1933,  as  amended.  Seller  agrees  that it will not sell or
transfer such shares of AMSC Common Stock,  except in accordance  with the terms
of the legend set forth below, unless such shares are subsequently registered or
an exemption from registration is available.  Seller is aware that the shares of
AMSC Common Stock it is receiving have not been registered  under the Securities
Act of 1933, as amended, or any state or other  jurisdiction's  securities laws,
and that the  shares  of AMSC  Common  Stock  must be held  indefinitely  unless
subsequently  registered or an exemption  from such  registration  is available.
Seller is aware that it will not be readily able to liquidate its shares of AMSC
Common Stock. Seller understands and agrees that the shares of AMSC Common Stock
to be received by Seller will bear legends substantially to the effect set forth
below and that a stop transfer order may be placed with respect thereto.


             THE SHARES OF COMMON STOCK  REPRESENTED  BY THIS  CERTIFICATE  HAVE
BEEN ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN  REGISTERED  UNDER THE SECURITIES
ACT OF 1933 OR THE  SECURITIES  LAWS OF ANY STATE,  AND MAY NOT BE  OFFERED  FOR
SALE, SOLD OR OTHERWISE  TRANSFERRED UNLESS  REGISTRATION  STATEMENTS UNDER SUCH
LAWS  ARE  THEN  IN  EFFECT  OR  UNLESS  AN  EXEMPTION  FROM  THE   REGISTRATION
REQUIREMENTS THEREOF IS THEN APPLICABLE TO SUCH OFFER OR SALE.

             The shares of Common Stock  represented  by  this  certificate  may
not be sold, transferred,  assigned, pledged, hypothecated or otherwise disposed
of except in  accordance  with the terms of the  Registration  Rights  Agreement
dated as of , 1998, a copy of which is on file at the office of the Corporation.



        ARTICLE 4. REPRESENTATIONS AND WARRANTIES OF AMSC AND PURCHASER

             AMSC and Purchaser each hereby represents and warrants to Seller as
follows:

             Section  4.1   Organization  and  Good  Standing.  Each of AMSC and
                            ---------------------------------
Purchaser is a corporation duly organized, validly existing and in good standing
under the laws of Delaware and has full corporate  power to conduct its business
as presently or then  conducted and to own and operate the assets and properties
now or then owned and operated by it.


             Section  4.2  Authority;   No  Required  Consents  or  Governmental
                           -----------------------------------------------------
Authorizations or Breach of Statute or Contract; Enforceability.
- ---------------------------------------------------------------

                    (a) Each of AMSC and Purchaser has the full corporate  power
and lawful authority to execute and deliver this Agreement and to consummate and
perform the transactions  contemplated hereby in the manner herein provided. The
execution  and  delivery  of  this  Agreement  by  AMSC  and  Purchaser  and the
consummation   and  performance  by  AMSC  and  Purchaser  of  the  transactions
contemplated  hereby in the manner  herein  provided  has been duly and  validly
authorized by all necessary corporate or other action.

                    (b) The AMSC Common Stock when issued to Seller will be duly
authorized,  validly  issued  free and  clear  of all  liens,  pledges,  claims,
security interests, options or other encumbrances of any nature whatsoever.

                    (c) Except for the applicable  requirements  of the HSR Act,
the AMSC Shareholder  Approval and, to the knowledge of AMSC and Purchaser,  the
Required  Consents,  neither the execution and delivery by AMSC and Purchaser of
this Agreement nor the consummation and performance by AMSC and Purchaser of the
transactions  contemplated hereby in the manner herein provided (i) requires the
approval,  consent or  authorization  of, or any  filing  with or notice to, any
federal,  state,  provincial,  local or other governmental agency or body or any
other third party, other than (A) approvals, consents,  authorizations,  filings
or notices of a character such that a failure to obtain, file or give them would
not  singly  or in the  aggregate  have a  material  adverse  effect on AMSC and
Purchaser  or  otherwise  impair or affect the  validity  of this  Agreement  or
prevent or hinder the consummation of the transactions  contemplated  hereby and
(B)  approvals,  consents,  authorizations,  filings or notices  which have been
obtained,  made or given,  or (ii)  conflicts with or will result in the uncured
and unwaived  breach or violation of any term or  provision  of,  constitutes  a
default under or will cause the acceleration of any payments pursuant to (A) the
Certificates of Incorporation or By-laws of AMSC and Purchaser, (B) any material
indenture,  mortgage,  deed of trust, lease, note or note agreement or any other
agreement or instrument to which either AMSC or Purchaser is a party or by which
either AMSC or Purchaser or any of their  respective  assets or  properties  are
bound,  (C) any  material  governmental  license,  franchise,  permit  or  other
authorization held by either AMSC or Purchaser or (D) any law, judgment,  order,
writ, injunction,  decree, award, rule or regulation of any court, arbitrator or
governmental agency or body applicable to either AMSC or Purchaser.

                    (d) This  Agreement,  when executed and delivered by Seller,
MAA and MAI and assuming the  enforceability  of this Agreement upon Seller will
be the  valid  and  binding  obligations  of AMSC  and  Purchaser,  and  will be
enforceable against AMSC and Purchaser in accordance with its terms,  subject to
bankruptcy,   insolvency  or  other  laws  affecting  the  rights  of  creditors
generally.

                    (e) Except as set forth on  Schedule  4.2,  there are no (i)
statutory,  contractual or other preemptive  rights with respect to the issuance
or transfer of any shares of AMSC Common Stock or other securities of AMSC; (ii)
outstanding  options,  warrants or rights to purchase,  repurchase  or otherwise
subscribe  for  any  equity  securities,  any  securities  convertible  into  or
exchangeable  for its capital stock or other ownership  interests of AMSC (other
than the  issuance  of AMSC Common  Stock  pursuant  to this  Agreement);  (iii)
obligations of AMSC, whether absolute or contingent,  to issue or repurchase any
shares of equity securities or other ownership interests or to share or make any
payments  based on its revenues,  profits or net income;  (iv)  indebtedness  or
securities  directly or  indirectly  convertible  into any equity  securities of
AMSC; or (v) voting trusts,  proxies,  or any other agreements,  restrictions or
understandings  with  respect to the voting of the capital  shares of AMSC or to
any other aspect of AMSC's affairs (including any registration rights).

               Section  4.3  Broker's  or  Finder's  Fees.  No  agent,   broker,
                             ----------------------------
investment banker,  person or firm acting on behalf of Purchaser,  AMSC or under
their authority is or will be entitled,  directly or indirectly, to collect from
or otherwise hold Seller, MAA, or MAI liable for any broker's or finder's fee or
any other  commission or similar fee in connection with any of the  transactions
contemplated herein.


             Section 4.4  Access; Sophistication; etc.
                          ----------------------------

                    (a) Seller, MAA and MAI have furnished to AMSC and Purchaser
copies  of  their  respective  most  recent  financial  statements  and AMSC and
Purchaser  in agreeing to accept the Shares  reviewed  such  documents  and have
relied only on (i) the statements and information contained therein and (ii) the
representations, warranties, terms and conditions of this Agreement.

                    (b)  Each  of  AMSC  and  Purchaser  acknowledges  that  all
documents,  books and records requested by AMSC or Purchaser  pertaining to MAA,
MAI and the  Subsidiaries  have been made  available for  inspection by AMSC and
Purchaser  and their agents and  representatives;  that AMSC and  Purchaser  and
their  agents  and  representatives  have had a  reasonable  opportunity  to ask
questions of and receive answers from Seller,  MAA, MAI and the  Subsidiaries or
officers or employees  acting on behalf of Seller,  MAA, MAI or the Subsidiaries
concerning the terms and conditions of the Shares and the business and prospects
of MAI, MAA and the Subsidiaries. AMSC and Purchaser and their respective agents
and representatives have such knowledge and experience in financial and business
matters as to enable them to utilize the  information  made available to them in
connection with the transactions contemplated hereby, to evaluate the merits and
risks of  accepting  the Shares and to make an informed  decision  with  respect
thereto and such an evaluation and informed decision have been made.

             Section 4.5 Investment  Representation.  Purchaser is acquiring the
                         --------------------------
Shares  to be  received  by  Purchaser  upon  consummation  of the  transactions
contemplated  herein for its own account for investment only and not with a view
to making a  distribution  thereof  within the meaning of the  Securities Act of
1933,  as  amended.  Purchaser  agrees  that it will not sell or  transfer  such
Shares,  except in  accordance  with the terms of the  legend  set forth  below.
Purchaser  is aware that the  Shares it is  receiving  have not been  registered
under  the  Securities  Act  of  1933,  as  amended,   or  any  state  or  other
jurisdiction's  securities  laws, and that the Shares must be held  indefinitely
unless  subsequently  registered  or an  exemption  from  such  registration  is
available.  Purchaser is aware that it will not be readily able to liquidate its
Shares.  Purchaser  understands  and agrees  that the Shares to be  received  by
Purchaser  will bear a legend  substantially  to the effect set forth  below and
that a stop transfer order may be placed with respect thereto.

             THESE SHARES HAVE NOT BEEN  REGISTERED  UNDER THE SECURITIES ACT OF
             1933,  AS  AMENDED,  OR  ANY  APPLICABLE   SECURITIES  LAW  OF  ANY
             JURISDICTION  AND MAY NOT BE  TRANSFERRED  UNTIL (A) A REGISTRATION
             STATEMENT UNDER SUCH SECURITIES ACT AND SUCH APPLICABLE  SECURITIES
             LAWS SHALL HAVE BECOME  EFFECTIVE WITH REGARD THERETO OR (B) IN THE
             OPINION  OF  COUNSEL   REASONABLY   ACCEPTABLE   TO  THE   COMPANY,
             REGISTRATION   UNDER  SUCH   SECURITIES  ACT  AND  SUCH  APPLICABLE
             SECURITIES  LAWS IS NOT REQUIRED IN  CONNECTION  WITH SUCH PROPOSED
             TRANSFER.

             Section 4.6  SEC Filings; Financial Statements.
                          ---------------------------------

                    (a)  AMSC has  made  available  to  Seller  a  complete  and
accurate copy of each report,  schedule,  registration  statement and definitive
proxy  statement  filed by AMSC  with the SEC on or after  January  1, 1996 (the
"AMSC SEC Reports"),  which are all the forms, reports and documents required to
be filed by AMSC with the SEC since such  date.  The AMSC SEC  Reports  complied
with the requirements of the Securities Act or the Exchange Act, as the case may
be at the times they were filed (or if amended or  superseded  by a filing prior
to the date of this Agreement then or the date of such filing).

                    (b) Each of the sets of  consolidated  financial  statements
(including,  in case, any notes  thereto)  contained in the AMSC SEC Reports was
prepared in accordance  with GAAP applied on a consistent  basis  throughout the
periods  involved and fairly presents in all material  respects the consolidated
financial  position of AMSC and its material  subsidiaries  as at the respective
dates thereof and the  consolidated  results of their  operations and cash flows
for  the  periods  indicated,   except  that  the  unaudited  interim  financial
statements were or are subject to normal year-end audit adjustments.

                    (c) AMSC has  previously  furnished to Seller a complete and
correct copy of any  amendments  or  modifications  that have not yet been filed
with the SEC but that are  required  to be filed in  agreements,  documents,  or
other  instruments which previously had been filed by AMSC with the SEC pursuant
to the Securities Act or the Exchange Act.

             Section 4.7  Absence of Certain Changes or Events.  Since September
                          ------------------------------------
30, 1997,  there has not been (a) any change,  or any development or combination
of  developments  of which  management of AMSC has  knowledge,  which has had or
would  reasonably be expected to have a material  adverse  effect on AMSC or (b)
any damages,  destruction or loss, whether or not covered by insurance which has
had or would reasonably be expected to have a material adverse effect on AMSC.

             Section  4.8   Absence  of   Undisclosed  Liabilities.   Except  as
                            --------------------------------------
disclosed in the AMSC SEC Reports or in this Agreement,  neither AMSC nor any of
its  Subsidiaries  has  liabilities or obligations,  either  accrued,  absolute,
contingent or otherwise,  except: 

                    (a) those liabilities or obligations set forth on the latest
balance sheet in the AMSC SEC Reports and not heretofore paid or discharged;

                      (b) liabilities arising in the ordinary course of business
under any agreement, contract, commitment, lease or plan; and

                    (c) those liabilities or obligations incurred,  consistently
with past business practice, in or as a result of the normal and ordinary course
of business since the date of the latest balance sheet set forth in the AMSC SEC
Reports.  For purposes of this Section,  the term  "liabilities"  shall include,
without limitation, any direct or indirect indebtedness,  guaranty, endorsement,
claim, loss, damage,  deficiency,  cost, expense,  obligation or responsibility,
known  or  unknown,  fixed  or  unfixed,  choate  or  inchoate,   liquidated  or
unliquidated, secured or unsecured.

             Section 4.9   Litigation.   Except  as  described  in  the AMSC SEC
                           ----------
Reports, no material litigation, arbitration, investigation, or other proceeding
of or before any court,  arbitrator or governmental or regulatory official, body
or authority is pending or, to the knowledge of AMSC, threatened against AMSC or
any of its Subsidiaries. Other than as so described, neither AMSC nor any of its
Subsidiaries is a party to or subject to the provisions of any judgment,  order,
writ, injunction or decre

                          ARTICLE 5. CERTAIN AGREEMENTS

             Section 5.1 Conduct of the Business. From the date hereof until the
                         ----------------------- 
Closing Date, except as otherwise contemplated by this Agreement or disclosed in
the Disclosure Schedule,  Seller shall, and shall cause MAA, MAI, ARDIS and each
of the  Other  Subsidiaries  to,  conduct  their  respective  businesses  in the
ordinary  course  consistent  with past practice and in such manner that, at the
Closing,  the representations and warranties of Seller shall be true and correct
in all  material  respects,  and  until  issuance  of a Final  Order,  AMSC  and
Purchaser  shall conduct the business of ARDIS in good faith.  Without  limiting
the  generality  of the  foregoing,  except as  otherwise  contemplated  by this
Agreement,  from the date  hereof  until the  Closing  Date,  without  the prior
written consent of AMSC and Purchaser, Seller will not permit MAA, MAI or any of
the Subsidiaries to:

                    (a) issue,  deliver,  sell,  dispose of, pledge or otherwise
encumber, or authorize or propose the issuance,  sale,  disposition or pledge or
other encumbrance of (x) any additional partnership interests or shares of their
capital  stock of any  class,  or any  securities  or rights  convertible  into,
exchangeable  for, or  evidencing  the right to  subscribe  for any  partnership
interests or shares of their capital stock,  or any rights,  warrants,  options,
calls,  commitments  or any other  agreements  of any  character  to purchase or
acquire  any  partnership  interests  or  shares of their  capital  stock or any
securities or rights convertible into, exchangeable for, or evidencing the right
to subscribe for, any partnership interests or shares of their capital stock, or
(y) any other  securities  in respect  of, in lieu of, or in  substitution  for,
partnership interests or shares outstanding on the date hereof;

                    (b) redeem,  purchase or  otherwise  acquire,  or propose to
redeem,  purchase or otherwise acquire, any of their outstanding  securities or,
in the case of MAA or MAI, to pay any dividends  (except for cash  dividends) or
make any other distributions to their respective shareholders;

                    (c) split,  combine,  subdivide or reclassify  any shares of
their capital stock;

                    (d) (i) grant any  increases in the  compensation  of any of
their  directors,  officers  or  employees,  except  in the  ordinary  course of
business,  (ii) pay or agree to pay any pension,  retirement  allowance or other
material  employee  benefit  not  required  by  any  of  the  existing  benefit,
severance,  pension or employment plans, agreements or arrangements as in effect
on the date hereof to any such director, officer or key employees,  whether past
or present, (iii) enter into any new or materially amend any existing employment
agreement with any such director,  officer or key employee,  (iv) enter into any
new or materially amend any existing severance agreement with any such director,
officer  or key  employee,  or (v)  except as may be  required  to  comply  with
applicable law, become obligated under any new Multiemployer Plan, Benefit Plan,
severance plan or arrangement,  which was not in existence on the date hereof or
amend by any such plan or  arrangement  in  existence  on the date hereof if the
effect thereof would be to enhance benefits thereunder;

                    (e)  adopt  a  plan  of  complete  or  partial  liquidation,
dissolution,  merger,  consolidation,  restructuring,  recapitalization or other
reorganization of MAA, MAI or any of the Subsidiaries;

                    (f) make any  acquisition by means of merger,  consolidation
or otherwise;

                    (g) adopt any  amendments  to their  Partnership  Agreement,
Certificate of Incorporation, charter or By-Laws;

                    (h) incur any  indebtedness  for borrowed money or guarantee
any such indebtedness or make any loans,  advances or capital  contributions to,
or investments  in, any other Person (other than to any of the  Subsidiaries  or
loans to their respective employees, in the ordinary course of business);

                    (i)  engage  in the  conduct  of  any  business  other  than
telecommunications and related businesses;

                    (j) enter into any agreement  providing for  acceleration of
payment or performance  or other  consequence as a result of a change of control
of MAA, MAI or any of the Subsidiaries;

                    (k) operate in other than the usual,  regular  and  ordinary
course and in accordance with past practices and, to the extent  consistent with
such operation and with the other covenants  contained  herein,  to use its good
faith  efforts to continue  normal  purchasing,  payments  of accounts  payable,
rental, leasing, renewal,  financing,  marketing,  advertising,  promotional and
maintenance  expenditures  with  respect  to the  business  of MAA,  MAI and the
Subsidiaries;  provided,  Seller  shall not on behalf of MAA,  MAI or any of the
Subsidiaries,  and shall not  permit  MAA,  MAI or any of the  Subsidiaries  to,
accelerate  or delay any payment of accounts  payable,  or bill any  customer in
advance beyond existing and usual contractual terms for services to be performed
after the date hereof;

                    (l) except as otherwise contemplated in this Agreement, fail
to maintain all authorizations and licenses materially necessary for the conduct
by MAA, MAI or the  Subsidiaries  of their  respective  businesses in accordance
with past custom and  practice,  including but not limited to failure to proceed
with any actions  necessary to ensure the  build-outs  referenced in the two FCC
orders,  each  dated  June 5,  1996,  granting  extensions  of time to  commence
services (No. 7110-02);

                    (m) fail to  maintain  all  insurance  policies  and binders
shown in Section  3.18 of the  Disclosure  Schedule  unless  new or  replacement
insurance policies or binders with similar coverage are obtained;

                    (n) submit or file with, except as otherwise contemplated in
this  Agreement,  or  otherwise  voluntarily  participate  as  a  party  to  any
stipulation, pleading, filing or other proceeding with the FCC, any state public
service  commission,  public utility  commission or similar state agency, or any
other regulatory  authority with  jurisdiction over MAA, MAI or the Subsidiaries
where such stipulation, pleading, filing or other proceeding could reasonably be
expected to result in a Threshold  Amount with respect to MAA, MAI or any of the
Subsidiaries or fail to notify AMSC promptly of any involuntary participation in
any of the foregoing;

                    (o) enter into any contract, agreement,  commitment or other
binding  arrangement  that would result in a liability  or financial  commitment
which in the aggregate exceeds $25,000, other than amounts reflected on MAA, MAI
or any Subsidiary's capital or operating budgets; or

                    (p) authorize,  recommend,  propose or announce an intention
to do any of the foregoing, or enter into any contract, agreement, commitment or
arrangement to do any of the foregoing.

             Section 5.2   Access  to  Information.   Subject to applicable law,
                           -----------------------
Seller,  MAA and MAI will  give AMSC and  Purchaser,  their  counsel,  financial
advisors, auditors and other authorized representatives reasonable access during
business hours after  reasonable  notice to the offices,  properties,  books and
records  of MAA,  MAI  and  each  of the  Subsidiaries  and  will  instruct  the
employees,   counsel  and  financial  advisors  of  Seller,  MAA,  MAI  and  the
Subsidiaries  to cooperate with AMSC and Purchaser in  theinvestigation  of MAA,
MAI and the Subsidiaries.


             Section 5.3  Efforts; Further Assurances; Permits.
                          ------------------------------------

                    (a) Subject to the terms and  conditions of this  Agreement,
each party will use all commercially  reasonable efforts to take, or cause to be
taken,  all  actions  and to do, or cause to be done,  all things  necessary  or
desirable under  applicable laws and regulations to consummate the  transactions
contemplated by this Agreement,  including,  without  limitation,  preparing and
making any filings required to be made under applicable law. Each of the parties
shall furnish to the other parties such  necessary  information  and  reasonable
assistance as such other party may request in connection with the foregoing.

                    (b) In case at any time after the  Closing  Date any further
action is necessary  or  desirable to carry out the purposes of this  Agreement,
AMSC,  Purchaser  and Seller shall,  and Seller shall cause the proper  officers
and/or directors of MAA, MAI and the Subsidiaries to, take all such necessary or
desirable action.

                    (c) Upon AMSC's or Purchaser's request, Seller will use, and
will cause MAA, MAI and the Subsidiaries to use, commercially reasonable efforts
to assist  AMSC and  Purchaser  in  obtaining  any  permits,  licenses  or other
authorizations  necessary for AMSC's and  Purchaser's  operation of MAA, MAI and
the Subsidiaries consistent with past practice after the Closing Date.

                    (d) In the event  that at any  time,  any  order,  decree or
injunction  shall be entered which prevents or delays the consummation of any of
the transactions  contemplated by this Agreement,  each party shall promptly use
its best  efforts to cause such  order,  decree or  injunction  to be  reversed,
vacated  or  modified  in  order to  permit  such  transactions  to  proceed  as
expeditiously as possible.

             Section 5.4 Books and Records.  AMSC, Purchaser and Seller agree to
                         -----------------  
retain for a period of three years or longer if otherwise  required by law after
the Closing  Date,  any and all Books and  Records  (hard  copy,  electronic  or
otherwise)  related to MAA, MAI and the  Subsidiaries  and in the  possession of
Seller, MAA, MAI or the Subsidiaries for all periods through the Closing Date or
related to the transactions contemplated hereby.  Notwithstanding the foregoing,
either  party may  notify the other of its desire to  discontinue  retention  of
specified documents in accordance with applicable record retention  requirements
during such period upon thirty days' written  notice and such party may elect to
assume  custody  thereof.  In the event any party needs access to such Books and
Records for purposes of verifying any representations  and warranties  contained
in  this  Agreement,   responding  to  inquiries  from  Governmental   Entities,
indemnifying, defending and holding harmless other parties hereto, in accordance
with applicable  provisions of this Agreement or any other  legitimate  business
purpose,  each party will allow  representatives  of the other parties access to
such books and records upon reasonable  notice during regular business hours for
the sole purpose of obtaining  information  for use as aforesaid and will permit
such other party to make such extracts and copies thereof as may be necessary or
convenient  and, if required for such purpose,  to have access to and possession
of original documents. 

Within 15  Business  Days  after the  Closing  Date,  Seller  shall  provide  to
Purchaser the Closing Financial Statements.

             Section 5.5  Governmental  Regulatory  Approvals.   As  promptly as
                          -----------------------------------
practicable after the date hereof,  AMSC, Purchaser and Seller shall, and Seller
shall cause MAA, MAI and the Subsidiaries to, file the required applications and
notices with the appropriate Governmental Entities as necessary for consummation
of the transactions contemplated by this Agreement (the "Regulatory Approvals").
To  the  extent   transferable,   Seller  will  transfer  any  existing  Non-FCC
Authorizations to Purchaser. Each party agrees to use its best efforts to obtain
the  Regulatory  Approvals  and the parties  agree to cooperate  fully with each
other and with all Governmental  Entities to obtain the Regulatory  Approvals at
the earliest practicable date.

             Section 5.6  FCC Consent.  As  promptly  as  practicable  after the
                          -----------
execution of this Agreement, the parties shall file all appropriate applications
and requests  with the FCC seeking,  and shall use their best efforts to obtain,
(i) the FCC's consent to the transfer of control of the licensed Subsidiaries to
Purchaser under the FCC Licenses (as listed in Section 3.23(b) of the Disclosure
Schedule),  and (ii) any necessary FCC waivers (all such consents or waivers are
collectively referred to as "FCC Consents").

             Section 5.7 HSR Act Review.  As promptly as  practicable  after the
                         --------------
execution  of this  Agreement,  the  parties  will make such  filings  as may be
required by the HSR Act with respect to the sale contemplated by this Agreement.
Thereafter,  the parties will file as promptly as practicable  any  supplemental
information  that may be requested by the U.S.  Federal Trade  Commission or the
U.S.  Department  of  Justice  pursuant  to the HSR Act.  The  parties  agree to
cooperate in seeking early termination of the waiting periods under the HSR Act.

             Section 5.8  Registration Rights. The Seller and AMSC shall execute
                          -------------------
a registration  rights  agreement,  substantially in the form attached hereto as
Exhibit B (the "Registration Rights Agreement").

             Section 5.9 Lock-up.  Seller hereby agrees not to transfer,  except
                         ------- 
to a  wholly-owned  Affiliate  of Seller  and  except  pursuant  to a  Piggyback
Registration  under the  Registration  Rights Agreement (as defined therein) and
except pursuant to Section 1 of that certain  Participation  Rights Agreement of
even date  herewith,  any  shares of AMSC  Common  Stock now owned or  hereafter
acquired by Seller during the one year period beginning on the Closing Date (the
"Lock-up Period"). Seller further agrees, during the Lock-up Period, not to (nor
will it permit  any  agent or  Affiliate  of Seller  to)  solicit,  initiate  or
encourage any  Acquisition  Proposal or furnish any information to, or cooperate
with,  any  Person,  corporation,  firm,  or other  entity  with  respect  to an
Acquisition Proposal,  unless Seller obtains prior written consent from AMSC. As
used  herein,  "Acquisition  Proposal"  means a  proposal  for a merger or other
business  combination  involving  AMSC or for the  acquisition  of a substantial
equity  interest in, or a  substantial  portion of the assets of,  AMSC.  Seller
shall promptly  communicate to AMSC the terms of any Acquisition  Proposal which
it may receive during such Lock-up Period.

             Section 5.10  Nonsolicitation.  During the period  beginning on the
                           ---------------
date hereof and ending on the  one-year  anniversary  of the  Closing  Date (the
"Nonsolicitation  Period"), Seller shall not, nor shall Seller permit any of its
officers,   directors,   employees,   Person  it   Controls,   agents  or  other
representatives  to,  directly or indirectly,  without prior written  consent of
AMSC,  (i)  actively  solicit  any  employee  of, or (ii)  actively  solicit any
employee who,  within the six months prior to the date of such  solicitation  or
hiring, had been an employee of, MAA, MAI or any of the Subsidiaries unless such
employee's  employment  was  terminated  by or at the request of MAA, MAI or any
Subsidiary.  It is  understood  that generic  advertising  shall not  constitute
"active  solicitation" for purposes of this Section 5.10. AMSC and Purchaser may
seek injunctive relief to prevent any such violations during the Nonsolicitation
Period and also may seek monetary  damages in respect of any  violations of this
Section 5.10.

Nothing in this Section 5.10 shall prevent Seller or any Person it controls from
hiring  any  such  employee  so long as such  hiring  is not the  result  of the
solicitation prohibited under this Section 5.10.

             Section 5.11  IBM Contract Renewal.   Seller shall  deliver to AMSC
                           --------------------
and Purchaser a fully executed  renewal of the services  contract by and between
ARDIS and  International  Business  Machines in  substance  and form  reasonably
satisfactory to Purchaser.


             Section 5.12  UPS  Contract.  Seller  shall  deliver  to  AMSC  and
                           -------------
Purchaser a fully  executed  services  contract by and between  ARDIS and United
Parcel  Service,  substantially  in  substance  and  form as  signed  by UPS and
previously provided to Purchaser (the "UPS Contract").

             Section 5.13  Escrow Agreement.  AMSC,  Purchaser  and Seller shall
                           ----------------
have executed the Escrow Agreement.

             Section 5.14 Employee  Transition.  Purchaser  shall provide,  as a
                          --------------------
general  matter,  compensation,  benefits  and  continued  employment  generally
comparable in the aggregate to those received by the employees of ARDIS prior to
the Closing,  consistent with Purchaser and AMSC's financial,  structuring,  and
organizational  considerations,  including  existing AMSC employee  compensation
considerations.  Promptly after the date hereof and prior to the Closing,  these
compensation  benefits and employment provisions will be presented to Seller. In
the event that  Purchaser  terminates  the  employment of a Management  Employee
within 12 months after the Closing Date, Purchaser shall provide such Management
Employee with the Severance Package (as defined below).  Promptly after the date
hereof and prior to the Closing,  the substantial terms of the severance package
for  Management  Employees  shall (i) be presented  to Seller and be  reasonably
acceptable to Seller and (ii) shall contain standard terms generally  offered to
management employees of similarly situated companies (the "Severance Package").

             Section 5.15   Updated Disclosure Schedule.   From  the date hereof
                            ---------------------------
until the Closing Date,  Seller shall  disclose to Purchaser and AMSC in writing
any material  variances from the  representations  and  warranties  contained in
Article  3 or  Article  8  hereof  promptly  upon  discovery  thereof,  and such
disclosures  shall update the Disclosure  Schedule for purposes of Articles 3, 7
and 8.


             Section 5.16  Nextel Proceeds.   ARDIS  has  entered  into an Asset
                           ---------------

Purchase  Agreement by and between  ARDIS and Nextel West Corp.,  dated July 11,
1997, which provides for the acquisition of certain ARDIS business  assets.  The
right of ARDIS to receive any and all  proceeds  under such  agreement  shall be
deemed for all  purposes to be assigned to Seller and (i) prior to the  Closing,
Seller  shall be entitled to collect and keep such  proceeds for its own account
(and cause ARDIS to cooperate in such regard) and (ii) prior to Closing,  Seller
may cause the Company to assign to Seller for payment from Nextel West Corp. the
proceeds from such agreement.


             Section 5.17 Non-Vendor  Intercompany Financing  Arrangements.  Any
                          ------------------------------------------------
non-vendor  financing  arrangement  existing as of the Closing between Seller or
any Seller Affiliate (other than the Subsidiaries),  on the one hand, and MAA or
MAI, on the other hand, is hereby cancelled and extinguished without any further
obligations related thereto on the part of MAA or MAI. I.

             Section 5.18  Intercompany Agreements.  Notwithstanding anything to
                           -----------------------
the contrary in any agreement between Ardis or Motorola entered into at any time
prior to the Closing Date:

                    (a) For the purpose of each such  agreement,  Seller  hereby
consents to the transactions contemplated by this Agreement.

                    (b) All such  agreements  shall  continue  in full force and
effect notwithstanding the transactions contemplated by this Agreement.  Without
limiting the generality of the foregoing, any provision limiting the application
of any such  agreement to ARDIS while it remains a subsidiary of Seller shall be
without force or effect.

                    (c) After the Closing  Date,  ARDIS may assign or  otherwise
transfer  any or all of its  rights  under  any such  agreements  to AMSC or any
Affiliate of AMSC that holds substantially all the assets of ARDIS, and if ARDIS
does so, such agreements shall continue in full force and effect notwithstanding
such transfer.



                                 ARTICLE 6. CONDITIONS TO CLOSING

             Section 6.1  Conditions to Obligation of Purchaser.  The obligation
                          -------------------------------------
of  Purchaser to purchase  the Shares  shall be subject to the  satisfaction  or
waiver by Purchaser of the following conditions:

                    (a) Representations and Warranties of Seller to be True.
                        ---------------------------------------------------
The  representations and warranties of Seller herein contained shall be true and
correct in all material respects on the date hereof and at the Closing Date with
the same effect as though  made at such time,  except (i) insofar as any of such
representations  and  warranties  are given as of a  particular  date and relate
solely  to a  particular  date or  period,  and (ii) to the  extent  any of such
representations  and  warranties  have been waived  hereunder or affected by the
transactions  contemplated or permitted herein. Seller shall have performed,  or
caused MAA, MAI and the  Subsidiaries to perform,  in all material  respects all
obligations  and  complied  in all  material  respects  with all  covenants  and
conditions  required by this  Agreement to be performed or complied with by them
at or prior to the Closing Date.

                    (b) No  Injunction  or  Other  Governmental  Action.  (i) No
                        -----------------------------------------------
preliminary or permanent  injunction,  decree or other order issued by any court
of competent  jurisdiction  or by any  governmental  or  regulatory  body or any
statute,  rule,  regulation  or executive  order  promulgated  or enacted by any
Governmental  Entity  after  the  date of this  Agreement  which  prohibits  the
consummation of the  transactions  contemplated  hereby shall be in effect;  and
(ii) no governmental  agency or body shall have instituted any suit,  action, or
legal or administrative proceeding to restrain, enjoin or otherwise question the
validity or legality of the  transactions  contemplated by this Agreement and no
order or  decree so  restraining  or  enjoining  such  transactions  shall be in
effect.

                    (c)   Statutory    Requirements;    Regulatory    Approvals;
                          ------------------------------------------------------
Contractual  Consents.  (i) All required waiting periods under the HSR Act shall
- ---------------------
have expired or been  terminated;  (ii) all  Regulatory  Approvals and all other
authorizations,  consents,  orders or approvals of, or  declarations  or filings
with, or expirations or terminations of waiting periods imposed by, the FCC, any
state public  service  commission,  public  utility  commission or similar state
agency,  or other  Governmental  Entities  necessary to effect the  transactions
contemplated by this Agreement shall have occurred,  been filed or been obtained
and become  Final  Orders,  provided,  that nothing in this  paragraph  shall be
deemed to prohibit  Closing upon issuance of the FCC  Authorization  pursuant to
the terms set forth in Section  2.6(a);  and (iii) all other  Required  Consents
shall have been obtained and shall be in full force and effect.

                    (d) Certificate.  Seller shall have delivered to Purchaser a
                        -----------
certificate to the effect that each of the conditions specified above in Section
6.1(a)-(c) has been satisfied in all respects; 

                    (e) Escrow Agreement. Seller and the Escrow Agent shall have
                        ----------------
executed the Escrow Agreement.

                    (f) IBM  Contract  Renewal.  Seller  shall have  delivered a
                        ----------------------
fully  executed  renewal  of the  services  contract  by and  between  ARDIS and
International Business Machines in substance and form reasonably satisfactory to
Purchaser. 

                    (g)  UPS  Contract.  Seller  shall  have  delivered  a fully
                         -------------
executed  services  contract  by and  between  ARDIS and United  Parcel  Service
substantially in substance and form as signed by UPS and previously  provided to
Purchaser.

                    (h) Directors and Non-Employee Officers.  Purchaser and AMSC
                        -----------------------------------
shall have  received  the  resignations,  effective  as of the  Closing,  of all
directors and non-employee officers of MAA, MAI and each of the Subsidiaries.

                    (i) AMSC Shareholder Approval. Purchaser shall have received
                        -------------------------
AMSC Shareholder Approval as and to the extent required.

                      (j)  Deliveries.   All actions to be taken by Seller,  MAA
                           ----------
and MAI in connection with consummation of the transactions  contemplated hereby
and all certificates,  opinions,  instruments,  and other documents  required to
effect the transactions  contemplated hereby will be reasonably  satisfactory in
form and substance to Purchaser.  Each of the deliveries  required under Section
2.7(b) shall have been prepared to the reasonable  satisfaction of Purchaser and
AMSC and their counsel.


                      (k) No  Material  Adverse  Change.  Since the date of this
                          -----------------------------
Agreement, there shall not have been any Material Adverse Change.

                    (l) Financing.  Purchaser shall have obtained,  on terms and
                        ---------
conditions  reasonably  satisfactory  to it,  financing  in the capital  markets
sufficient to consummate the transactions contemplated hereby.


             Purchaser may waive any condition  specified in this Section 6.1 if
Purchaser executes a writing so stating at or prior to Closing.

             Section 6.2  Conditions to Obligations of Seller.   The  obligation
                          -----------------------------------
of Seller to sell the Shares shall be subject to the  satisfaction  or waiver by
Seller of the following conditions:


                    (a)  Representations and Warranties of Purchaser and AMSC to
                         -------------------------------------------------------
Be True.  The  representations  and  warranties  of  Purchaser  and AMSC  herein
- -------
contained shall be true and correct in all material  respects on the date hereof
and at the Closing Date with the same effect as though made at such time, except
(i)  insofar as any of such  representations  and  warranties  are given as of a
particular  date and relate solely to a particular  date or period,  and (ii) to
the extent any of such representations and warranties have been waived hereunder
or affected by the  transactions  contemplated  or  permitted  herein.  AMSC and
Purchaser  shall have  performed in all material  respects all  obligations  and
complied in all material respects with all covenants and conditions  required by
this  Agreement  to be  performed  or  complied  with by them at or prior to the
Closing Date.

                    (b) No  Injunction  or  Other  Governmental  Action.  (i) No
                        -----------------------------------------------
preliminary  or  permanent  injunction  or other  order  issued  by any court of
competent  jurisdiction  or by any  governmental  or  regulatory  body  nor  any
statute,  rule,  regulation  or executive  order  promulgated  or enacted by any
Governmental  Entity  after  the  date of this  Agreement  which  prohibits  the
consummation of the  transactions  contemplated  hereby shall be in effect;  and
(ii) no governmental  agency or body shall have instituted any suit,  action, or
legal or administrative proceeding to restrain, enjoin or otherwise question the
validity or legality of the  transactions  contemplated by this Agreement and no
order or  decree so  restraining  or  enjoining  such  transactions  shall be in
effect.

                    (c) Statutory  Requirements;  Regulatory Approvals.  (i) All
                        ----------------------------------------------
required  waiting  periods  under  the  HSR  Act  shall  have  expired  or  been
terminated;   (ii)  all  Regulatory  Approvals  and  all  other  authorizations,
consents,   orders  or  approvals  of,  or  declarations  or  filings  with,  or
expirations or  terminations  of waiting  periods imposed by, the FCC, any state
public service commission, public utility commission or similar state agency, or
other Governmental Entities necessary to effect the transactions contemplated by
this Agreement shall have occurred, been filed or been obtained and become Final
Orders,  provided,  that nothing in this  paragraph  shall be deemed to prohibit
Closing upon issuance of the FCC  Authorization  pursuant to the terms set forth
in  Section  2.6(a);  and (iii)  all other  Required  Consents  shall  have been
obtained and shall be in full force and effect.

                    (d) Certificate.  Purchaser shall have delivered to Seller a
                        -----------
certificate to the effect that each of the conditions specified above in Section
6.2(a)-(c) has been satisfied in all respects.

                    (e)  Registration  Rights.  AMSC  shall  have  executed  the
                         --------------------
Registration Rights Agreement.

                    (f) Escrow Agreement.  Purchaser,  AMSC and the Escrow Agent
                        ----------------
shall have executed the Escrow Agreement on or prior to the date hereof.

                    (g)  Deliveries.  All actions to be taken by  Purchaser  and
                         ----------
AMSC in connection with consummation of the transactions contemplated hereby and
all certificates,  opinions, instruments, and other documents required to effect
the transactions contemplated hereby will be reasonably satisfactory in form and
substance to Seller.  The  deliveries  required  under Section 2.7(a) shall have
been prepared to the reasonable satisfaction of Seller and its counsel.


                    (h) Minimum  Stock  Price.  The Market  Value of AMSC Common
                        ---------------------
Stock as of the Closing Date shall be at least 70% of the Market Value as of the
date hereof,  after taking into account all stock  splits,  reverse stock splits
and similar adjustments to the number of shares of AMSC Common Stock outstanding
on the date hereof.





                           ARTICLE 7. INDEMNIFICATION

             Section 7.1  Indemnification by Seller.   Seller  shall  indemnify,
                          -------------------------
defend and hold Purchaser and their Affiliates harmless from and against any and
all liabilities,  losses, damages, costs and expenses  (collectively,  "Losses")
asserted against, imposed on, or incurred or suffered by Purchaser,  MAA, MAI or
the Subsidiaries as a result of any of the following:

                    (a) the  inaccuracy of any  representation  or the breach of
any warranty set forth in Article 3 or in any agreement or certificate  executed
and delivered by Seller pursuant to this Agreement;

                    (b)  the   non-fulfillment   of  any  unwaived  covenant  or
agreement on the part of Seller set forth in this  Agreement or in any agreement
or certificate executed and delivered pursuant to this Agreement; and

                    (c)  any  and  all  actions,  suits,  claims,   proceedings,
investigations,  audits, examinations,  demands, assessments,  fines, judgments,
settlements,  interest,  penalties,  costs,  remedial actions and other expenses
(including  without  limitation  reasonable audit,  engineering,  consulting and
legal fees) pertaining to or arising out of any of the foregoing.

             Section 7.2  Indemnification by AMSC.  AMSC shall indemnify, defend
                          -----------------------
and hold Seller and its Affiliates  harmless from and against any and all Losses
asserted  against,  imposed  on,  or  incurred  or  suffered  by  Seller or such
Affiliates as a result of any of the following:

                    (a) the  inaccuracy of any  representation  or the breach of
any warranty set forth in Article 4 or in any agreement or certificate  executed
and delivered by AMSC or Purchaser pursuant to this Agreement;

                    (b) the nonfulfillment of any unwaived covenant or agreement
on the part of AMSC or Purchaser set forth in this Agreement or in any agreement
or certificate executed and delivered pursuant to this Agreement; and

                    (c)  any  and  all  actions,  suits,  claims,   proceedings,
investigations,  audits, examinations,  demands, assessments,  fines, judgments,
settlements,  interest,  penalties,  costs,  remedial actions and other expenses
(including  without  limitation  reasonable audit,  engineering,  consulting and
legal fees) pertaining to or arising out of any of the foregoing.

              Section  7.3   Limitations  on  Indemnification  for  Breaches  of
                             ---------------------------------------------------
Representations and Warranties.
- ------------------------------

             The  following  indemnification   provisions  shall  apply  to  all
breaches of representations,  warranties or covenants by Seller (including those
in Article 8), except those  contained in Sections 3.1, 3.2, 3.3, 3.4, or 3.5 or
as  otherwise  specifically  provided  in this  Agreement,  and all  breaches of
representations,  warranties or covenants of Purchaser and AMSC (including those
in Article 8),  except  those  contained in Sections 4.1 and 4.2 or as otherwise
specifically provided in this Agreement:

                    (a) No Indemnitor shall be liable for indemnification  until
the total amount of Losses  incurred by the  Indemnitee  exceeds  $300,000  (the
"Indemnification   Threshold  Amount")  provided  that  if  the  Indemnification
Threshold  Amount is exceeded with respect to Losses for which an Indemnitor has
an  indemnification  obligation  under  this  Article 7 or  Article 8, then such
Indemnitor's  obligation  shall include the full amount of such Losses as if the
limitation contained in this subsection (a) did not exist.

                    (b) Except as provided under Section  7.3(c),  no Indemnitor
shall be  liable  for  indemnification  payments  under  any  provision  of this
Agreement  to  the  extent  such  aggregate  indemnification  payments  by  such
Indemnitor exceed $10,000,000.

                    (c)  Notwithstanding  any other provision in this Agreement,
there shall be no limit for indemnification  payments with respect to any breach
of the representations  and warranties  contained in Section 3.25 or pursuant to
Section 8.7(i) hereof.

               Section  7.4  Survival of  Representations  and  Warranties.  The
                             ---------------------------------------------
representations  and  warranties of the parties hereto shall survive the Closing
and shall, except as otherwise specifically set forth in this Agreement,  expire
two years after the Closing Date, except as otherwise  specifically  provided in
this  Agreement.   Notwithstanding   the  preceding,   the  representations  and
warranties   set  forth  in  Sections  3.7,  3.8,  3.9,  3.10  (except  for  the
representations  and  warranties  pursuant to the first sentence of such Section
3.10, the survival period of which shall be two years),  3.11, 3.12, 3.13, 3.14,
3.15, 3.17, 3.18, 3.20, 3.24, 3.25, 3.26, 3.27, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8 and
4.9 shall expire one year after the date hereof.

               Section  7.5  Method  of   Asserting   Claims.   All  claims  for
                             -------------------------------
indemnification   by  a  party   entitled  to  be   indemnified   hereunder  (an
"Indemnitee")  by  another  party  hereto (an  "Indemnitor"),  except for claims
relating to Taxes which shall be governed by the  provisions of Article 8, shall
be asserted and resolved as follows:

                    (a) In the  event  that any  claim or  demand  for  which an
Indemnitee  may claim  indemnity  is asserted  against or sought to be collected
from an Indemnitee by a third party,  the Indemnitee shall notify the Indemnitor
within 20 days  following the receipt by the Indemnitee of such claim or demand,
specifying  the nature of such  claim or demand and the amount or the  estimated
amount  thereof  to the  extent  then  feasible  (which  estimate  shall  not be
conclusive  of the final amount of such claim and demand) (the "Claim  Notice").
Failure of an Indemnitee  to so notify an  Indemnitor  within such 20-day period
shall not relieve an  Indemnitor of its  obligation to indemnify the  Indemnitee
for such claim or demand except to the extent that the delay in giving notice of
such claim or demand in fact materially prejudices (i) the defense of such claim
or demand  where the  Indemnitor  has the right to control  such defense or (ii)
participation  in the defense of such claim or demand where the Indemnitor has a
right of  participation.  Any  party  hereto  against  whom a claim or demand is
asserted  by  a  third  party   shall,   without   prejudice  to  any  right  of
indemnification  hereunder,  appropriately  respond  to  such  claim  or  demand
(whether by answer,  denial,  request for  extension of time or other action) to
such claim or demand within any  applicable  time period,  so as to preserve any
rights or remedies it or any other party may have against the person making such
claim or demand.

                    (b) An Indemnitor  shall have thirty (30) days from the date
on which the Claim  Notice is duly  given  (the  "Notice  Period")  to notify an
Indemnitee (i) whether or not it disputes the liability of the Indemnitor to the
Indemnitee  hereunder  with  respect to such claim or demand and (ii) whether or
not the  Indemnitor  desires,  at its  sole  cost and  expense,  to  defend  the
Indemnitee  against such claim or demand.  If an  Indemnitor  does not notify an
Indemnitee  within the Notice  Period  that it  disputes  its  liability  to the
Indemnitee,  the  Indemnitor  shall be liable  for the  amount of any  resulting
Losses.

                    (c) In the event an Indemnitor notifies an Indemnitee within
the Notice Period that it desires to defend the Indemnitee  against such a claim
against or demand from the Indemnitee,  then except as hereinafter  provided the
Indemnitor  shall  defend,  at its sole  cost and  expense,  the  Indemnitee  by
appropriate proceedings,  shall use its best efforts to settle or prosecute such
proceedings  to a final  conclusion in such a manner as to avoid any risk of the
Indemnitee (or MAA, MAI or the  Subsidiaries,  if a Purchaser is the Indemnitee)
becoming  subject to any  injunctive  or other  equitable  order or relief or to
liability for any other  matter,  and shall control the conduct of such defense;
provided,  however,  that the  Indemnitor  shall not,  without the prior written
consent of the  Indemnitee,  consent to the entry of any  judgment  against  the
Indemnitee or enter into any settlement or compromise which does not include, as
an  unconditional  term thereof,  the giving by the claimant or plaintiff to the
Indemnitee of a release,  in form and substance  reasonably  satisfactory to the
Indemnitee,  from all liability in respect of such claim or  litigation.  If the
Indemnitee  desires to  participate  in, but not  control,  any such  defense or
settlement, it may do so at its sole cost and expense.

                    (d) Prior to an  Indemnitor's  settling  any claim or demand
the defense of which it has assumed  control,  the  Indemnitor  shall obtain the
Indemnitee's  approval,  confirmed  in  writing  in  accordance  with the notice
provisions hereof, which approval shall not be unreasonably withheld or delayed.
If an Indemnitee  notifies an Indemnitor of its disapproval of such  settlement,
the Indemnitee  shall  thereupon  become liable,  from and after the date of its
disapproval, for the amount of any award, judgment, costs or expenses (including
attorney  fees) in excess of the proposed  settlement  amount and shall have the
right  to  elect to  control  the  defense  of such  claim at its sole  cost and
expense.

                    (e) In the event an  Indemnitee  should have a claim against
an Indemnitor  hereunder which does not involve a claim or demand being asserted
against  or sought  to be  collected  from the  Indemnitee  (or MAA,  MAI or the
Subsidiaries, if a Purchaser is the Indemnitee) by a third party, the Indemnitee
shall promptly send a Claim Notice with respect to such claim to the Indemnitor.
If the Indemnitor  does not notify the Indemnitee  within the Notice Period that
it disputes  such claim,  the  Indemnitor  shall be liable for the amount of any
resulting Losses.

             Section  7.6  Method of  Payment.  Any  indemnification  payment by
                           ------------------
Purchaser  to Seller  pursuant  to this  Article 7 or Article 8 shall be made in
immediately available funds. Any indemnification  payment by Seller to Purchaser
pursuant to this Article 7 or Article 8 shall be made (i) first,  in AMSC Common
Stock received by Seller  pursuant to this  Agreement,  and (ii) second,  to the
extent such indemnification payment amount exceeds the aggregate Market Value of
the AMSC Common Stock held by Seller, in immediately available funds;  provided,
however,  that any indemnification  payments by Seller to Purchaser with respect
to any breach of the representations and warranties contained in Section 3.25 or
pursuant to Section 8.7(i) shall be made in  immediately  available  funds.  For
purposes  of  any  indemnification  payment  made  by  Seller  pursuant  to  the
immediately preceding sentence,  the Market Value of the AMSC Common Stock shall
be calculated  as the higher of (A) the Market Value as of the date hereof,  and
(B) the Market Value as of the date of such indemnification payment.

             Section 7.7  Limitation of Recourse.
                          ----------------------

                    (a)  Following  the  Closing,  except with respect to claims
based upon fraud, the  indemnification  provided by Article 7 or Article 8 shall
be the sole and exclusive remedy for any Losses of any party hereto with respect
to any  misrepresentation or inaccuracy in, or breach of, any representations or
warranties  or any  breach or  failure  in  performance  prior to Closing of any
covenants or agreements made by any party in this Agreement or in any exhibit or
schedules hereto or any certificate delivered hereunder.

                    (b) No  claim  shall be  brought  or  maintained  by AMSC or
Purchaser  or their  respective  successors  or  permitted  assigns  against any
officer,  director or employee  (present or former) of any of the  Companies  or
Seller,  or by Seller or its respective  successors or permitted assigns against
any officer,  director or employee (present or former) of Purchaser or AMSC, and
no recourse shall be brought or granted  against any such persons,  by virtue of
or based upon any alleged misrepresentation or inaccuracy in or breach of any of
the  representations,  warranties or covenants of any of the Companies or Seller
on the one hand, or Purchaser or AMSC on the other hand,  set forth or contained
in this Agreement or any exhibit or schedule hereto or any certificate delivered
hereunder,  except to the  extent  that the same  shall  have been the result of
fraud by any such Person (and in the event of such fraud, such recourse shall be
brought or granted solely against the Person or Persons committing such fraud).

             Section 7.8  Acknowledgment by Seller,  Purchaser and AMSC. Seller,
                          ---------------------------------------------
Purchaser  and  AMSC  each  hereby  acknowledges  that it has  conducted  to its
satisfaction,  an independent  investigation  and  verification of the financial
condition, results of operations, assets, liabilities,  properties and projected
operations  of  AMSC  and  the  Companies,  respectively,  and in  making  their
respective  determination to proceed with the transactions  contemplated by this
Agreement,  (i)  Seller  has  relied  on  the  results  of its  own  independent
investigation  and verification and the  representations  and warranties of AMSC
and Purchaser  expressly and specifically set forth in this Agreement,  and (ii)
Purchaser  and AMSC have each  relied on the  results  of their own  independent
investigation and verification and the  representations and warranties of Seller
and the Companies  expressly and specifically set forth in this Agreement.  SUCH
REPRESENTATIONS  AND WARRANTIES BY SELLER AND THE COMPANIES ON THE ONE HAND, AND
BY AMSC AND  PURCHASER  ON THE OTHER  HAND,  CONSTITUTE  THE SOLE AND  EXCLUSIVE
REPRESENTATIONS  AND  WARRANTIES  OF  SUCH  PARTIES  TO  THE  OTHER  PARTIES  IN
CONNECTION  WITH  THE   TRANSACTIONS   CONTEMPLATED   HEREBY,   AND  EACH  PARTY
UNDERSTANDS,   ACKNOWLEDGES  AND  AGREES  THAT  ALL  OTHER  REPRESENTATIONS  AND
WARRANTIES  OF ANY KIND OR  NATURE  EXPRESSED  OR  IMPLIED  (INCLUDING,  BUT NOT
LIMITED  TO, ANY  RELATING  TO THE  FUTURE OR  HISTORICAL  FINANCIAL  CONDITION,
RESULTS OF OPERATIONS,  ASSETS OR LIABILITIES OF THE COMPANIES) ARE SPECIFICALLY
DISCLAIMED BY SELLER AND THE COMPANIES AND OF AMSC ARE  SPECIFICALLY  DISCLAIMED
BY AMSC AND PURCHASER.


                             ARTICLE 8. TAX MATTERS

             Section 8.1   Seller's Tax Representations and Warranties.   Seller
                           -------------------------------------------
hereby represents and warrants to AMSC that:

                    (a)  For the  period  from  its  incorporation  through  the
Closing  Date,  MAI was and will remain a member of the Seller Group and was and
will be included in the  consolidated  federal  income tax returns of the Seller
Group.

                    (b)  For the  period  from  its  incorporation  through  the
Closing  Date,  MAA was and will remain a member of the Seller Group and was and
will be included in the  consolidated  federal  income tax returns of the Seller
Group.

                    (c) For the period from their formation  through the Closing
Date,  each of ARDIS  Holding  and ARDIS was and will remain a  partnership  for
federal and State income Tax purposes.

                    (d) Except as set forth on Section  8.1(d) of the Disclosure
Schedule,  all Tax Returns  required to have been filed by the Companies and any
affiliated, consolidated, combined, unitary or other groups of which any Company
is, will be (at any time on or prior to the  Closing  Date) or was a member have
been or will be filed  timely  and are or will be  accurate  and  correct in all
material respects insofar as they relate to the Companies,  and, insofar as they
relate to the Companies,  all Taxes due and payable (for taxable  periods ending
on or before the Closing Date and for that portion of any Split Period ending on
the Closing  Date) by any Company and any  affiliated,  consolidated,  combined,
unitary  or other  groups of which any  Company  is,  will be (at any time on or
prior to the Closing Date) or was a member (i) have been or will be paid or (ii)
adequate  reserves and/or  liabilities have been or will be established for such
Taxes on the financial books and records of the Companies.

                    (e) Each of the Companies has  established  (and through the
Closing Date will  establish) on its Financial  Statements  and other  financial
books and records reserves and/or  liabilities that are adequate for the payment
of all Taxes not yet due and payable for taxable periods ending on or before the
Closing  Date and for that  portion of any Split  Period  ending on the  Closing
Date.

                    (f) Prior to the Closing Date,  each of the  Companies  will
pay Taxes at such  times  and in such  manner  as are  consistent  with its past
practices.

                    (g) Except as set forth on Section  8.1(g) of the Disclosure
Schedule, no waivers of statutes of limitation have been given or requested with
respect to any Tax  Returns  covering  any  Company or any Taxes  payable by any
Company.

                    (h) Except as set forth on Section  8.1(h) of the Disclosure
Schedule or for matters that have been resolved, no deficiency or adjustment for
any unpaid Taxes of any Company has been proposed, asserted or assessed.

                    (i) There are no Liens  with  respect to Taxes  (except  for
such Liens for Taxes as are disclosed in Section 3.12 of the Disclosure Schedule
and except for Liens for Taxes,  assessments or other  governmental  charges not
yet delinquent) upon any of the properties or assets,  real,  personal or mixed,
tangible or intangible, of the Companies.

                    (j) Except as set forth on Section  8.1(j) of the Disclosure
Schedule,  no Company (i) is or will become a party to any  agreement  providing
for the allocation or sharing of, or  indemnification  for, Taxes, or (ii) is or
prior to the Closing will become required to include in income any adjustment in
tax periods  ending  after the Closing  Date  pursuant to Section  481(a) of the
Code.

                    (k) No  formal  or  informal  plan of  liquidation  has been
adopted by any Company.

                    (l) Except as set forth on Section  8.1(l) of the Disclosure
Schedule,  neither Seller nor any Company:  (i) has filed a consent  pursuant to
Section 341(f) of the Code or agreed to have Section 341(f)(2) of the Code apply
to any disposition of a subsection (f) asset (as such term is defined in Section
341(f)(4) of the Code) owned by a Company; and (ii) has executed or entered into
a closing agreement  affecting a Company pursuant to Section 7121 of the Code or
any predecessor  provision thereof or any similar  provision of State,  local or
foreign law.

                    (m)  Within   twenty  (20)  days  after  the  date  of  this
Agreement,  Seller shall  provide to AMSC a schedule of all tax  elections  that
have been made with  respect to any Company (or any  predecessor  thereof)  that
would have any effect on such Company after  December 31, 1996,  but only to the
extent that such elections were made  affirmatively  by the filing of a separate
document  evidencing  any such  election.  In  addition,  Seller  shall  use all
commercially  reasonable  efforts to  identify  to AMSC in writing  within  such
twenty  (20)  day  period  any  other  such  tax  elections  that  were not made
affirmatively  by  the  filing  of  a  separate  document  evidencing  such  tax
elections.

                    (n) Except as set forth on Section  8.1(n) of the Disclosure
Schedule,  neither  Seller nor any Company has  received  written  notice to the
effect that the  Company is subject to any  penalty by reason of a violation  of
any Tax order, Tax rule or Tax regulation or with respect to any Tax Return.


               Section  8.2  AMSC's Tax  Representations  and  Warranties.  AMSC
                             --------------------------------------------
hereby represents and warrants to Seller that:

                    (a)  Except  for  any   transaction   contemplated  by  this
Agreement (e.g., an election under Section  338(h)(10) of the Code),  AMSC shall
cause the Companies not to engage in any transaction outside the ordinary course
of  business on the Closing  Date after the  Closing if such  transaction  would
increase  the tax  liability  of any of the  Companies  for any Taxable  Year or
portion  thereof ending on the Closing Date.  AMSC and Seller agree to treat any
transaction  of the  Companies  which is (i) - - outside the ordinary  course of
business and (ii) occurs on the Closing Date but after the Closing as occurring,
for federal  income Tax purposes,  at the beginning of the day after the Closing
Date, in accordance with Treasury Regulations Section 1.1502-76(b)(1)(ii)(B).

                    (b) To the  knowledge of AMSC,  the fair market value of the
shares of AMSC Common Stock and other consideration  received by Seller pursuant
to the Merger will be  approximately  equal to the fair market  value of the MAA
Shares surrendered pursuant to the Merger in exchange therefor.

                    (c) To the knowledge of AMSC, following the Merger, MAA will
hold at least 90 percent of the fair market value of Merger Sub's net assets and
at least 70 percent of the fair market  value of Merger  Sub's gross assets held
immediately prior to the Merger.  For purposes of this  representation,  amounts
used by Merger Sub to pay Merger-related  expenses will be included as assets of
Merger Sub immediately prior to the Merger.

                    (d) Immediately prior to the Merger, AMSC will be in control
of Merger Sub within the meaning of Section 368(c) of the Code.

                    (e) AMSC has no plan or intention  to  reacquire  any of the
shares of AMSC Common Stock issued in the Merger.

                    (f)  As of the  date  of  this  Agreement  and at all  times
through and including the effective time of the Merger, AMSC had and has no plan
or intention of causing or permitting  MAA to issue  additional  shares of stock
that would result in AMSC (or any permissible transferee thereof) losing control
of MAA within the meaning of Section  368(c) of the Code.  Except as provided in
the next  sentence,  at any time during the eighteen  (18) months  following the
Closing Date, if AMSC causes or permits MAA to issue additional  shares of stock
such that AMSC (or any  permissible  transferee  thereof)  loses  control of MAA
within the  meaning of Section  368(c) of the Code,  AMSC  shall,  prior to such
issuance,  provide an opinion of Arnold & Porter,  or other  counsel  reasonably
acceptable to Seller, that such issuance of additional shares will not cause the
Merger  to  fail  to  qualify  as  a  tax-free   reorganization   under  Section
368(a)(2)(E)  of the Code. The second  sentence of this Section 8.2(f) shall not
apply if, prior to such issuance of additional  shares of MAA stock,  Seller and
its  Affiliates do not own at least fifty percent (50%) of the AMSC Common Stock
received  by  Seller in the  Merger.  (g) AMSC has no plan or  intention  (i) to
liquidate  MAA,  (ii) to sell or otherwise  dispose of the MAA Shares except for
transfers of such shares to  corporations  controlled by AMSC, or (iii) to cause
MAA to sell or  otherwise  dispose  of any of its assets or of any of the assets
acquired from Merger Sub, except for dispositions made in the ordinary course of
business or transfers of assets to a  corporation  controlled  by MAA within the
meaning of Section 368(c) of the Code.

                    (h) Merger Sub will have no liabilities  assumed by MAA, and
will not transfer to MAA any assets subject to liabilities, in the Merger.

                    (i)  Following  the Merger,  MAA will  continue its historic
business  or use a  significant  portion of its  historic  business  assets in a
business.

                    (j) AMSC and Merger Sub will pay their respective  expenses,
if any, incurred in connection with the Merger.

                    (k) There is no intercorporate indebtedness existing between
AMSC and MAA or between Merger Sub and MAA that was issued, acquired, or will be
settled at a discount.

                    (l) AMSC does not own, nor has it owned during the past five
years, any shares of the stock of MAA.

                    (m) Neither AMSC nor Merger Sub is an investment  company as
defined in Section 368(a)(2)(F)(iii) and (iv) of the Code.

                    (n) AMSC shall cause each of the  representations  contained
in Section  8.2(a)  through  (m) to be true  through the  effective  time of the
Merger.

               Section 8.3 Tax Returns, Audits, Contests, Etc.; Tax Cooperation;
                           -----------------------------------------------------
Tax Sharing Agreements; Tax Records.
- -----------------------------------

                    (a)  Seller  shall  prepare  and file  timely or cause to be
prepared  and filed  timely (i) all Tax Returns of or  including  any Company or
Benefit Plan for any Taxable Year  (including  any Short  Taxable  Year) the due
date (including extensions) for which is on or before the Closing Date, (ii) the
federal income Tax Returns of the Companies (e.g., Forms 1065 and separate Forms
1120 for inclusion in the consolidated  federal income Tax Returns of the Seller
Group) for any Taxable Year - - (including  any Short Taxable Year) ending on or
before  the  Closing  Date,  and  (iii)  all Tax  Returns  for  any  affiliated,
consolidated,  combined,  unitary or other group of which any Company is, was or
will be a member  prior to the  Closing  Date  (other  than any Tax Return for a
Taxable Year ending after the Closing Date for such a group that consists solely
of two or more of the  Companies).  In addition  to the Tax  Returns  that it is
required to file under the  immediately  preceding  sentence,  Seller may, on or
before the Closing Date, file any Tax Return of or including any Company for any
Taxable  Year  (including  any Short  Taxable  Year)  that ends on or before the
Closing Date.

                    (b) (i) AMSC shall be responsible  for the  preparation  and
filing of all Tax Returns of the Companies that are due  (including  extensions)
after the Closing  Date,  other than (A) Tax Returns  that Seller is required to
file under the first  sentence of Section 8.3(a) and (B) Tax Returns that Seller
has filed on or before the  Closing  Date  pursuant  to the second  sentence  of
Section 8.3(a), provided, however, that AMSC shall have no obligation to prepare
any Tax Return for any affiliated, consolidated, unitary or other group of which
any  Company is, was or will be a member  prior to the Closing  Date (other than
any Tax Return that is due  (including  extensions)  after the Closing  Date for
such a group that consists solely of two or more of the Companies).

                         (ii) At the Closing,  Seller shall  provide AMSC with a
list of all unfiled Tax Returns for or including  any Company for Taxable  Years
ending on or before the Closing Date.

                         (iii) If, pursuant to Section 8.7(a),  Seller is liable
to  indemnify  AMSC for any Taxes shown on a Tax Return that AMSC is required to
file under Section 8.3(b)(i), AMSC shall use all commercially reasonable efforts
to provide  Seller with a copy of any such Tax Return  (along with a computation
of the amount of Tax shown on such Tax Return for which Seller is responsible) a
reasonable  time prior to the filing  thereof.  AMSC shall use all  commercially
reasonable  efforts to provide  any such  income Tax Return at least  sixty (60)
days prior to the due date thereof.  AMSC will consider any  suggestion  made by
Seller with respect to the calculations and positions taken in such Tax Returns.
Failure by AMSC to comply with the provisions of this Section  8.3(b)(iii)  will
in no way eliminate, limit or restrict Seller's indemnification  obligations set
forth in Section 8.7.

                    (c) (i)  Seller  shall pay or cause to be paid (A) all Taxes
of the Companies or Taxes for which any Company may be liable that are due on or
before the  Closing  Date,  and (B) the federal  and State  income  Taxes of the
Companies for any Taxable Year  (including  any Short Taxable Year) ending on or
before the Closing Date.

                         (ii) No later than 180 days following the Closing Date,
AMSC  shall  provide  to Seller a federal  income Tax  computation  and  related
schedules  and data for each Company  having a Short  Taxable Year ending on the
Closing Date,  which Tax computation  shall be consistent with Tax Returns filed
for prior  Taxable  Years and shall  reflect  the  income,  gain or loss of such
Company for that Short Taxable Year other than any income,  gain or loss arising
or resulting from any election described in Section 8.4.

                         (iii)  Seller  shall  use all  commercially  reasonable
efforts to complete  prior to the Closing Date all necessary  federal income Tax
computations  and related  schedules  and data for each  Company for the Taxable
Years of the Companies  ending on December 31, 1997. To the extent necessary for
Seller to  complete  such  computations,  schedules  and data,  AMSC shall allow
Seller and its agents  reasonable access after the Closing Date to the books and
records of the Companies.

                         (iv)  Except as  provided  in Section  8.3(c)(i),  AMSC
shall pay or cause to be paid all Taxes of the Companies  that are due after the
Closing Date.

                         (v) The  provisions of this Section 8.3(c) shall not be
construed  or applied to limit or broaden  the  indemnification  obligations  of
either Seller or AMSC under Section 8.7 except as specifically provided therein.
All Tax Returns and computations referred to in this Article 8 shall be prepared
in a manner  consistent with prior Tax Returns,  insofar as such Tax Returns and
computations referred to in this Article 8 relate solely to the Companies.

                    (d) AMSC and Seller  shall use all  commercially  reasonable
efforts to provide each other with copies of Tax Returns  (including amended Tax
Returns)  of or  including  any  Company to the extent any such Tax  Returns are
relevant  in  determining  either  party's  obligations  under  this  Agreement,
including,  but not limited to, the  indemnification  obligations in Section 8.7
and the  procedural  obligations  in this Section 8.3.  The  provisions  of this
Section  8.3  shall  not be  construed  or  applied  to  limit  or  broaden  the
indemnification obligations of either Seller or AMSC under Section 8.7 except as
specifically provided therein.

                    (e)  Seller  and AMSC  shall  provide  prior  notice to, and
cooperate fully with,  each other in connection  with any audit  examinations of
any Company by any  governmental  taxing  authority  with  respect to any Taxes,
including  but not limited to the  furnishing  or making  available  of records,
books of account or other  materials  reasonably  necessary  or helpful  for the
defense  against  the  assertions  of any  taxing  authority  as to any Taxes or
deficiencies thereof.

                    (f) Seller and AMSC shall  cooperate  with one  another  and
their respective  representatives,  in a prompt and timely manner, in connection
with the preparation, signing, and filing of, and any administrative or judicial
proceeding involving, any Tax Return filed or required to be filed by or for (i)
the Seller  Group,  any member  thereof,  or any Company  for any  Taxable  Year
(including any Short Taxable Year) ending on or before the Closing Date, or (ii)
the AMSC  Group,  any  member  thereof,  or any  Company  for any  Taxable  Year
(including  any Short Taxable Year) ending after the Closing Date,  with respect
to any item or issue  affecting the property or operations of any Company.  Such
cooperation shall include,  but not be limited to, making available to the other
party,  during normal business hours,  all books,  records  (including,  but not
limited to, working papers and schedules),  information,  officers and employees
(without  substantial  interruption  of  employment)  reasonably  requested  and
necessary or useful in connection  with any Tax inquiry,  audit,  investigation,
dispute,  litigation  or any other  matter  requiring  any such books,  records,
information,   officers  or  employees  for  any  reasonable  business  purpose.
Notwithstanding the foregoing, neither party shall be required to furnish to the
other Tax Returns or drafts thereof of the Seller Group,  the AMSC Group, or any
affiliated,  consolidated, combined, unitary or other group of which any Company
is, will be or was a member,  as the case may be, for any Taxable  Year,  except
that each party shall furnish to the other the  applicable  portions of such Tax
Returns reporting the operations of the Companies and the applicable portions of
all reports  relating to the examination by the IRS or any other federal,  State
or local governmental  agency. Any information obtained pursuant to this Article
8 shall be held in strict confidence and shall be used solely in connection with
the reason for which it was requested.

                    (g) As of the  Closing  Date,  any and all  Tax  sharing  or
allocation  agreements shall terminate as between any Company,  on the one hand,
and  Seller  or any  Affiliates  thereof,  on the  other  hand,  for  all  Taxes
regardless  of the  Taxable  Year for  which  such  Taxes are  imposed,  and the
provisions of this Agreement shall apply thereafter.

                    (h) (i) AMSC  shall  not,  and  shall not  permit  any other
person or entity to, dispose of or destroy any of the business records and files
of any Company in existence on the Closing Date  relating to Taxes without first
offering to turn over  possession  thereof to Seller by written notice to Seller
at least 30 days prior to the proposed date of such disposition or destruction.

                         (ii) Seller  shall not,  and shall not permit any other
person or entity to,  dispose  of or  destroy  any  business  records  and files
relating  to Taxes of any  Company  now in the  possession  of, or  subsequently
acquired by, either  Seller,  any member of the Seller Group or any Affiliate of
Seller without first offering to turn over possession thereof to AMSC by written
notice to AMSC at least 30 days prior to the proposed  date of such  disposition
or destruction.

             Section 8.4  Asset Purchase Treatment for MAI Shares.
                          ---------------------------------------

                    (a) (i) At the sole  election of  Purchaser,  Purchaser  and
Seller  shall elect for federal Tax  purposes to treat the  purchase and sale of
the MAI Shares  pursuant to this  Agreement as a purchase and sale of the assets
of MAI in accordance  with the provisions of Code Section 338 generally and Code
Section 338(h)(10) specifically. If an election is to be made as provided in the
preceding  sentence,  Purchaser  and Seller  agree to make timely all  elections
necessary to carry out the  provisions  of this Section  8.4(a)(i) and to report
the purchase and sale of the MAI Shares  consistent with the preceding  sentence
and in accordance with the provisions of this Article 8.

                         (ii) If  Purchaser  and  Seller  make the  election  in
Section  8.4(a)(i),  then Purchaser and Seller shall elect, for State income Tax
purposes,  to treat the  purchase  and sale of the MAI Shares as a purchase  and
sale of the assets of MAI to the  extent  permitted  by  applicable  law.  If an
election is to be made as  provided in the  preceding  sentence,  Purchaser  and
Seller agree to make timely all elections  necessary to carry out the provisions
of this Section 8.4(a)(ii) and to report the purchase and sale of the MAI Shares
consistent with the preceding  sentence and in accordance with the provisions of
this  Article 8. In any  State(s)  where it is unclear  whether  applicable  law
permits the  purchase and sale of the MAI Shares to be treated as a purchase and
sale of assets, Purchaser and Seller agree to treat the purchase and sale of the
MAI Shares as a purchase and sale of the assets of MAI provided  that Seller and
Purchaser otherwise make the election described in Section 8.4(a)(i).

                         (iii) The  provisions of Section  8.4(b),  (c), (d) and
(e) below shall apply if Seller and  Purchaser  make an  election  described  in
Section 8.4(a)(i) or (ii).

                    (b) Seller  shall pay or  otherwise be liable for (and shall
indemnify and hold harmless AMSC, its  subsidiaries  and the Companies  against)
any and all Taxes and Other Tax Costs  attributable to the recognition of income
by Seller or any Company  (and  Seller  shall  receive the tax benefit  from any
loss)  from  the  treatment  of the  purchase  and sale of the MAI  Shares  as a
purchase  and sale of the assets of MAI in  accordance  with the  provisions  of
Section 8.4(a).

                    (c)  Purchaser and Seller hereby agree to determine the fair
market value of the assets,  both  tangible and  intangible,  of MAI (and of any
partnership Affiliates of MAI and MAA) (the "Assets") for purposes of allocating
the  consideration  to be paid for, and the amount  realized on the sale of, the
Assets. This determination,  which shall be binding upon Purchaser and Seller in
accordance with the provisions of Section 1060(a) of the Code,  shall be made as
follows:

                         (i) No later  than  sixty (60) days (or such later date
as the parties mutually agree) following the Closing Date, Purchaser shall cause
an appraiser (the "Appraiser"),  which shall be reasonably acceptable to Seller,
to provide to Purchaser and Seller an appraisal of the fair market valuations of
the Assets (the  "Appraisal").  For purposes of this Section  8.4(c),  the "fair
market  value" of an Asset shall mean the amount a willing  buyer would pay to a
willing  seller for the actual  property in question (and not  calculated  based
solely  upon  the  replacement  cost  for  such  property)  in an  arm's  length
transaction  where  each  party to the  transaction  has full  knowledge  of all
relevant information concerning such property.

                         (ii) Each of  Seller  and  Purchaser  may  provide  the
Appraiser  with such  information as it believes will be useful to the Appraiser
in preparing  the  Appraisal.  Copies of any written  materials  provided to the
Appraiser by either Seller or Purchaser shall  simultaneously be provided to the
other party.  All oral  communication  with the Appraiser  shall be made through
Purchaser, which shall provide Seller with reasonable opportunities to speak and
meet with the  Appraiser  to express any views  Seller  reasonably  believes are
pertinent to the preparation of the Appraisal.

                         (iii)   Purchaser  shall  pay  the  basic  fee  of  the
Appraiser as set at the time the Appraiser is initially engaged by Purchaser. To
the extent that any additional  fees, costs or expenses are incurred as a result
of documents provided by Seller,  communications initiated by Seller or meetings
held at Seller's request, Seller shall pay such fees, costs or expenses.

                         (iv)  The  fair   market   valuations   of  the  Assets
determined  by the Appraiser  pursuant to this Section  8.4(c) shall be the fair
market  valuations  of the Assets  for Tax  purposes  and shall be binding  upon
Seller and Purchaser as provided in this Agreement.

               (d) Neither  Seller nor  Purchaser nor any Affiliate of Seller or
Purchaser  shall take a position in any Tax  proceeding,  Tax audit or otherwise
inconsistent  with the fair market  value  determinations  described  in Section
8.4(c);  provided,  however,  that (i) nothing  contained  herein shall  require
Seller or Purchaser to contest any  challenge to such  determinations,  and (ii)
nothing  contained  herein  shall  prevent  Seller,  Purchaser,  or any of their
Affiliates  from  filing  protective  amended  Tax Returns or claims for refunds
after a Tax authority has challenged such determinations.  In the event that any
claim shall be made by any taxing  authority  against  either  Purchaser  or any
Company (or any successor  thereto),  on the one hand,  or Seller,  on the other
hand,  that, if  successful,  would have the effect of altering such fair market
value  determinations,  then  the  party  that  is the  subject  of  such  claim
("Involved  Party") shall give notice thereof to the other party ("Other Party")
in writing  within 30 business days thereof.  Thereafter,  except as provided in
the next sentence, the Involved Party shall have control of any contest relating
thereto,  but the  Involved  Party  shall  consider in good faith any request or
suggestion by the Other Party for any conference, hearing or proceeding relating
to such contest,  shall (to the extent it is feasible to do so) permit the Other
Party to participate  therein at such Other Party's expense and shall not object
to such  Other  Party's  submission  of briefs  and  memoranda  of law  relating
thereto,  and  shall  provide  the Other  Party  with any  relevant  information
reasonably requested by such Other Party.  Notwithstanding the provisions of the
preceding  sentence,  the Other Party shall have control of any contest relating
to the fair market valuations if the Involved Party has notified the Other Party
that the  Other  Party is  obligated  under the  provisions  of  Section  8.7 to
indemnify  the  Involved  Party for any Tax  liability  relating to the proposed
adjustments  to the fair  market  valuations  and the  Other  party  shall  have
provided  to the  Involved  Party  the  written  notice  and  acknowledgment  of
financial responsibility referred to in the first sentence of Section 8.7(g).

               (e)  Purchaser  and Seller  each  agrees to prepare  and file all
Internal  Revenue  Service  forms and the  required  schedules  thereto  and all
requisite State and local forms and schedules  ("Forms") required to be filed by
either or both of them  providing  for the treatment of the purchase and sale of
the MAI  Shares as  purchases  and sales of the  Assets in  accordance  with the
provisions of Section 8.4(a). Purchaser shall request in writing from Seller, or
Seller shall  request in writing from  Purchaser,  any  information  (reasonably
within the knowledge or possession of the person from whom requested)  necessary
to complete the Forms, which information shall be provided no later than 30 days
following any such request. All such Forms shall be prepared consistent with the
fair market valuations of the Assets determined under Section 8.4(c),  provided,
however,  that Seller and Purchaser each recognize that appropriate  adjustments
will be made for  transaction  and other costs and as required by any applicable
laws or regulations in determining  the amount  realized upon the disposition of
the Assets or the amount paid for the Assets.

             Section 8.5   Tax-Free Reorganization Treatment for the MAA Merger.
                           ----------------------------------------------------
Seller  and AMSC agree that they  intend  that the Merger  qualify as a tax-free
reorganization  described in Section  368(a)(2)(E)  of the Code,  and Seller and
AMSC  shall  file all Tax  Returns in a manner  consistent  with such  treatment
(including  satisfying  all  reporting  requirements  necessary  to obtain  such
treatment).  Neither  Seller nor AMSC nor any  Affiliate of Seller or AMSC shall
take a position in any Tax proceeding,  Tax audit or otherwise inconsistent with
the  treatment  of the  Merger as a  tax-free  reorganization  qualifying  under
Section  368(a)(2)(E) of the Code;  provided,  however,  that nothing  contained
herein  shall  prevent  Seller,  AMSC,  or any of their  Affiliates  from filing
protective  amended Tax Returns or claims for refund after a Tax  authority  has
challenged such treatment.

             Section 8.6  Transfer Taxes.  Notwithstanding  any other  provision
                          --------------
in this  Agreement,  Seller  and  AMSC  shall  each be  responsible  for and pay
one-half of any transfer  taxes,  recording  taxes,  bulk sale taxes and similar
transaction taxes resulting from the transfer of the MAI Shares,  the MAA Shares
or the deemed  transfer of the equity  interests in or the assets of any Company
as a result of the  transactions  contemplated  by this  Agreement.  Each  party
hereto hereby shall pay all such taxes and file all necessary  documentation  as
required  under the  applicable  statutory  provisions  with respect to all such
taxes in a timely  manner.  Not later than fifteen (15) business days  following
receipt  of  written  notice  from  AMSC or  Seller  that it has paid any  Taxes
described  in this  Section  8.6,  the  other  party  shall pay to the payor its
one-half share of such Taxes.

             Section  8.7  General Tax Indemnifications.
                           ----------------------------

               (a)  Seller  shall  indemnify  and  hold  harmless  AMSC  and its
Affiliates  (including  the  Companies)  from and against any and all Taxes with
respect to which any Company or any entity as successor thereto may be liable to
the extent  such  Taxes are (i)  attributable  to any breach of any of  Seller's
representations,  warranties  or  covenants  contained  in this  Article 8, (ii)
payable with respect to any Taxable Year ending on or prior to the Closing Date,
or (iii)  payable with respect to that portion of any Split Period that is prior
to and including the Closing Date. Seller shall also indemnify and hold harmless
AMSC and its Affiliates  (including the Companies) from and against (iv) any and
all Other Tax Costs relating to any Taxes described in this Section 8.7(a),  and
(v) any and all Taxes and Other Tax Costs  arising in any  Taxable  Year  ending
after the Closing Date that result from any  adjustment  to any Tax Return of or
including the Company for any Taxable Year ending on or before the Closing Date,
provided,  however, that the indemnification  pursuant to this Section 8.7(a)(v)
shall not apply to the extent that such adjustment  relates to whether any asset
is depreciable or  amortizable,  and further  provided that any Tax or Other Tax
Cost  indemnifiable  under any other  provision  of this  Article 8 shall not be
indemnifiable a second time under this Section  8.7(a)(v),  and further provided
that any  indemnification  pursuant to this Section 8.7(a)(v) shall not apply to
any  adjustment  involving  any agreement  with a tax authority  unless it has a
Material   Adverse   Effect  on  any   Company  (or  any   successor   thereto).
Notwithstanding  the preceding,  Seller shall not be obligated to indemnify AMSC
or any of its Affiliates  (including  the  Companies)  for, in the case of taxes
described  in clauses  (ii),  (iii),  (iv) and (v),  any Taxes that  result from
AMSC's breach of any representation or warranty contained in this Article 8.

               (b)  AMSC  shall  indemnify  and  hold  harmless  Seller  and its
Affiliates from and against any and all Taxes with respect to which Seller,  any
of Seller's  Affiliates,  any Company or any entity as successor  thereto may be
liable to the  extent  such Taxes are (i)  attributable  to any breach of any of
AMSC's  representations or warranties  contained in this Article 8, (ii) insofar
as they relate to any Company or any entity as successor  thereto,  payable with
respect to any Taxable  Year  beginning  and ending after the Closing  Date,  or
(iii) insofar as they relate to any Company or any entity as successor  thereto,
payable  with  respect to that portion of any Split Period that begins after the
Closing  Date.  AMSC  shall  also  indemnify  and hold  harmless  Seller and its
Affiliates  from and  against  (iv) any and all Other Tax Costs  relating to any
Taxes  described in this Section  8.7(b).  Notwithstanding  the preceding,  AMSC
shall not be obligated to indemnify  Seller or any of its Affiliates for, in the
case of taxes  described in clauses (ii),  (iii) and (iv), any Taxes that result
from Seller's breach of any representation or warranty contained in this Article
8. For purposes of this Section  8.7(b),  if AMSC's  obligation to indemnify for
Taxes  arises as a result of the Merger  failing to qualify as a  reorganization
under Section 368(a) of the Code, such obligation  shall be limited to an amount
that reflects the value of the timing  difference  between (x) the year in which
such  Taxes  are  actually  payable  and (y) the year or  years in which  Seller
disposes of the AMSC Common Stock received by Seller in the merger,  adjusted to
take into account any Tax benefit Seller may realize from the early payment.

               (c) If the Seller's indemnification obligation under this section
8.7  arises  in  respect  of any  adjustment  (i) for  which  AMSC or any of its
Affiliates  (including any of the Companies) receives  indemnification  from the
Seller and (ii) which  results in any Tax  benefit to AMSC or any  Affiliate  of
AMSC  (including  any of the  Companies)  thereof for any Taxable  Year or Split
Period  beginning  after  the  Closing  Date  which  would  not,  but  for  such
adjustment,  be  available,  AMSC shall pay, or shall  cause to be paid,  to the
Seller an amount equal to the actual Tax saving  produced by such Tax benefit at
the time such Tax saving is realized by AMSC or any of its Affiliates (including
any of the Companies).  The amount of any such Tax saving for any Taxable period
shall be the amount of the reduction in Taxes  payable to a taxing  authority by
AMSC or any of its  Affiliates  (including  any of the  Companies)  thereof with
respect to such Taxable Year or Split Period as compared to the Taxes that would
have  been  payable  to a  taxing  authority  by AMSC  or any of its  Affiliates
(including  any of the  Companies)  with  respect to such  Taxable Year or Split
Period in the absence of such Tax benefit.

               (d) For  purposes of this  Section  8.7, in the case of any Taxes
that are  payable  with  respect to a Split  Period,  the  portion of such Taxes
allocable to Seller or to the portion of the Split Period  ending on the Closing
Date  shall be equal to (i) in the case of Taxes  imposed on the basis of income
or receipts,  an amount  determined on the basis of a closing of the books as of
the end of the Closing Date and (ii) in the case of any other Taxes, the product
of the total Taxes for the period  multiplied  by a fraction  the  numerator  of
which is the number of days in the Split  Period  from the  commencement  of the
Split Period through and including the Closing Date and the denominator of which
is the number of days in the entire Split Period  (provided,  however,  that for
purposes of this clause (ii)  appropriate  adjustments  shall be made to reflect
specific events that can be identified and  specifically  allocated as occurring
on or prior to the Closing Date (in which case Seller shall be  responsible  for
any Taxes  related  thereto) or occurring  after the Closing Date (in which case
AMSC shall be responsible for any Taxes related thereto)).  Notwithstanding  any
other provision in this Section 8.7(d), Section 8.2(a) or any other provision in
this Agreement,  any income,  gain, gross receipts,  net receipts or similar Tax
item  recognized  by any  Company as a result of any  transaction  described  in
Section 5.17 shall be treated as recognized by such Company for all Tax purposes
exclusively in (x) Taxable Years ending on or prior to the Closing Date,  and/or
(y) those  portions of Split Periods that are prior to and including the Closing
Date.

               (e)  Seller or AMSC,  as the case may be (the "Tax  Indemnitee"),
shall notify the other party (the "Tax  Indemnitor")  in writing in a reasonably
prompt  fashion  of any  written  inquiries,  notices  of audit,  assertions  of
liability,  or other written  communications  from or with a Tax authority  that
relate to Taxes with  respect to which the Tax  Indemnitor  may be liable  under
this Article 8 (a "Tax Claim").  Failure by the Tax Indemnitee to notify the Tax
Indemnitor  as  required  by  this  Sectio  8.7(e)  shall  not  relieve  the Tax
Indemnitor of its liability and obligation to indemnify the Tax Indemnitee under
this Agreement unless such failure  precludes the Tax Indemnitor from contesting
the Taxes giving rise to its indemnification  obligation and there is at least a
reasonable   possibility  that  the  Tax  Indemnitor  would  have  prevailed  in
challenging such Taxes.

               (f) Seller and AMSC shall take all  reasonable  steps and actions
necessary or  appropriate  to minimize any  indemnification  obligations  either
party may have under this Section 8.7.

               (g) Except as provided in the next  sentence,  within thirty (30)
days of receiving  notice of a Tax Claim,  the Tax Indemnitor,  at its sole cost
and expense, may elect, by written notice to the Tax Indemnitee,  to assume sole
responsibility for defending such Tax Claim, but only if, in such written notice
to the Tax  Indemnitee,  the  Tax  Indemnitor  acknowledges  full  and  complete
financial  responsibility  for all Taxes covered by such Tax Claim and all Other
Tax Costs  related  thereto.  Notwithstanding  the  provisions  of the preceding
sentence,  Seller shall not have the rights to settle or litigate any Tax Claim,
or to control and  determine  the timing and amount of any payment or deposit of
an amount relating to any Tax Claim, the submission or content of documentation,
returns or other Tax forms,  protests,  memoranda of law and briefs, the conduct
of  oral  arguments  or  presentations,  the  selection  of  witnesses  and  the
negotiation  of  stipulations  of fact with  respect to any Taxable  Year ending
after  the  Closing  Date.  If the Tax  Indemnitor  assumes  responsibility  for
defending a Tax Claim  pursuant to this  Section  8.7(g),  it shall keep the Tax
Indemnitee  reasonably  informed  of the status of such Tax  Claim,  and the Tax
Indemnitee and its  representatives  shall be entitled to attend any meetings or
hearings involving the Tax Claim at its own expense.  If the Tax Indemnitor does
not elect to assume  control of defending any Tax Claim,  the Tax Indemnitee may
settle  or defend  such Tax  Claim.  In such a case,  if the Tax  Indemnitor  is
responsible  for the  asserted  Taxes under this  Article 8, the Tax  Indemnitor
shall  indemnify the Tax Indemnitee for the reasonable  cost of its defense,  in
addition to the underlying Taxes.

               (h)  Any   unresolved   dispute   relating  to  any  payments  or
indemnification  obligations  of either Seller or AMSC to the other  pursuant to
the  provisions of this Article 8 shall be submitted to an  arbitrator  mutually
acceptable  to Seller and AMSC (or,  if the  parties are unable to agree upon an
arbitrator,  to an arbitrator selected by the American Arbitration Association).
Any such  arbitration  shall be  conducted in  accordance  with the rules of the
American Arbitration Association in effect at the time of the arbitration. Where
any dispute  relates to a position to be taken on any Tax Return of or including
a Company,  the  parties  shall use  reasonable  efforts to resolve  the dispute
informally or pursuant to  arbitration  prior to filing such Tax Return.  In the
event the  parties  are  unable to  resolve  any  dispute  prior to filing a Tax
Return,  the position  taken on the Tax Return shall have no impact or influence
on the  resolution  of the  underlying  dispute,  and in no way shall  prejudice
either  party's  rights  or  obligations  under  this  Article  8, nor shall any
resolution of any dispute have any impact on how a Tax Return must be filed.  In
the event an  indemnification  dispute arises that is based on a disagreement as
to  how  a  Tax  Return  of  or  including  a  Company  should  be  filed,   the
indemnification  obligations  of the  indemnifying  party under this Section 8.7
shall be determined  consistent with the filing position  advanced by such party
if such  position is not  inconsistent  with prior Tax  Returns  and  accounting
conventions and is proper and legal. If a Tax authority subsequently  determines
that  the  position  advanced  by  the  indemnifying  party  is  incorrect,  the
indemnifying party's obligation to indemnify the other party shall be determined
consistent with the determination of the Tax authority.

               (i) Notwithstanding Section 8.7(b), AMSC shall not be responsible
for,  and Seller  shall  indemnify  and hold  harmless  AMSC and its  Affiliates
(including the Companies)  from and against any and all Taxes or Other Tax Costs
with  respect to which any  Company or any entity as  successor  thereto  may be
liable to the extent such Taxes arise in any Taxable Year ending  after  Closing
Date that result from any income, net receipts,  gross receipts, gain or similar
items recognized by any Company as a result of the transactions  contemplated in
Section 5.16.

               (j) AMSC and Seller  agree to cooperate in good faith in carrying
out the provisions of this Article 8.

               (k) This  Article 8 shall be  construed  and applied to avoid any
double  counting of any payments,  credits or other benefits with respect to any
representation, warranty, covenant or indemnity set forth herein.

             Section 8.8  Exclusive Remedy for Taxes.   Except  as  provided  in
                          --------------------------
Section 7.3, this Article 8 provides the  exclusive  agreement  between  Seller,
AMSC and their respective  Affiliates regarding  responsibility for the Taxes of
the Companies.


             Section  8.9  Survival and Purchase Price Adjustment.
                           --------------------------------------

                    (a)  Notwithstanding  any other provision of this Agreement,
the covenants,  promises,  indemnifications and other obligations of the parties
hereto set forth in this Article 8 shall survive the Closing until fully carried
out and the expiration of any applicable statute of limitations  relating to the
Taxes covered thereby.

                    (b) In the event any payments are made to Seller pursuant to
the provisions of this Article 8, such payments are  adjustments to the purchase
price paid for the MAI Shares as set forth in Section 2.2(B).


                 ARTICLE 9. TERMINATION OF AGREEMENT; PAYMENT OF
                               EXPENSES; WAIVER OF CONDITIONS

               Section  9.1  Termination  Pre-Closing.  Anything  herein  to the
                             ------------------------
contrary  notwithstanding,  this  Agreement may be terminated at any time before
the Closing Date as follows  (such date of  termination  being the  "Termination
Date"), and in no other manner:


                    (a) Mutual  Consent.  By mutual written consent of Purchaser
                        ---------------
and Seller.

                    (b) Expiration Date. By either  Purchaser or Seller,  if the
                        ---------------
Closing shall not have occurred on or before June 30, 1998.

                    (c) Early Expiration Date. By Seller, if the Purchaser shall
                        ---------------------
have not  provided  to Seller a waiver or evidence  (satisfactory  to Seller) of
satisfaction  of the  condition  set forth in Section  6.1(l) on or prior to the
later of (i) 60 days after the end of the initial FCC comment period relating to
the  transactions   contemplated   hereby,  and  (ii)  14  days  after  the  FCC
Authorization,  for any reason  other than the breach or  inaction  of the party
seeking to exercise its termination rights under this Section 9.1.

                    (d)  Prohibition.  By  written  notice of  either  Seller or
                         -----------
Purchaser  if there shall have been entered a Final Order or  injunction  of any
Governmental   Entity   restraining  or  prohibiting  the  consummation  of  the
transactions  contemplated  hereby,  including but not limited to the failure of
the parties to obtain an FCC Authorization.
                        

                    (e) Breach;  Failure of  Condition.  Purchaser may terminate
                        ------------------------------
this  Agreement  by giving  written  notice  to Seller at any time  prior to the
Closing in the event Seller is (and AMSC and Purchaser are not) in breach in any
material  respect,  and Seller may terminate  this  Agreement by giving  written
notice to Purchaser  at any time prior to the Closing in the event  Purchaser or
AMSC  is  (and  Seller  is  not)  in  breach  in any  material  respect,  of any
representation, warranty, or covenant contained in this Agreement and, in either
case, such breach has not been fully cured by the breaching party within 30 days
after written notice of such breach has been delivered to the breaching party by
the terminating party;

                    (f) Share Price.  Seller may terminate this Agreement on the
                        -----------
Closing Date if the Market Value of a share of AMSC Common Stock  calculated  as
of the Closing  Date has  declined  by more than 30% from the Market  Value of a
share of AMSC Common Stock  calculated as of the date hereof,  after taking into
account all stock splits,  reverse stock splits and similar  adjustments  to the
number of shares of AMSC Common Stock outstanding on the date hereof.

                    (g) FCC Final Order.  Seller or Purchaser may terminate this
                        ---------------
Agreement in the event that a Final Order of the FCC has not been received when,
under the terms of the Escrow  Agreement,  any period of time  applicable to the
Escrowed Funds has expired  thereby  causing a return of the Escrowed  Funds, by
providing notice to such other party within 30 Business Days of such expiration.
In the event a termination occurs pursuant to this Section 9.1(g):


                         (i) Purchaser shall return the Shares to Seller;

                         (ii) Seller shall  return to Purchaser  the AMSC Common
Stock  issued to Seller  for the MAA  Shares  pursuant  to the terms of  Section
2.1(a); and

                         (iii) each of the parties  shall have only those rights
and obligations held by such party prior to the Closing Date.


               Section  9.2  Termination  Post-Closing.  In the  event  that the
                             -------------------------
Closing proceeds upon receipt of an FCC Authorization that is not a Final Order,
and an adverse Final Order of the FCC is received that will not permit Purchaser
to  operate  MAA,  MAI and  the  Subsidiaries  as  contemplated,  Purchaser  may
terminate this  Agreement by providing  notice to Seller within 30 Business Days
of  receipt  of the  adverse  Final  Order  of the  FCC.  In  the  event  that a
termination occurs pursuant to this Section 9.2:


                    (a) the Escrow Agent shall return the MAI Purchase  Price to
the Purchaser;

                    (b) Purchaser shall return the Shares to Seller;

                    (c) Seller shall  return to Purchaser  the AMSC Common Stock
issued to Seller for the MAA Shares pursuant to the terms of Section 2.1(a); and

                    (d)  each   parties   shall  have  only  those   rights  and
obligations held by such party prior to the Closing Date.


             Section 9.3 Payment of Expenses;  Waiver of Conditions.  (a) Except
                         ------------------------------------------
as set forth in  Section  9.3(b),  in the event  that  this  Agreement  shall be
terminated  pursuant to this Article 9, all  obligations  of the parties  hereto
under this  Agreement  shall  terminate  and there shall be no  liability of any
party to any other  party  hereto and each party  hereto  will pay all costs and
expenses  incident to its  negotiation  and preparation of this Agreement and to
its performance of and compliance  with all agreements and conditions  contained
herein  on its part to be  performed  or  complied  with,  including  the  fees,
expenses  and  disbursements  of its counsel,  its  auditors and its  actuaries;
provided,  however,  that if this  Agreement  shall be  terminated  pursuant  to
Section  9.1(b),  such  termination  shall not release any party hereto from any
liability  that  such  party  may have  for any  breach  occurring  prior to the
Termination Date of any representation,  warranty or covenant made by such party
in this Agreement.

                    (b) In the event this  Agreement is  terminated  pursuant to
Section 9.1(c),  then Seller shall be entitled to be reimbursed by Purchaser for
its expenses  incurred in connection  with the  negotiation and execution of and
otherwise in connection with this Agreement which expenses shall be deemed to be
equal to  $4,000,000  in  immediately  available  funds,  which  funds  shall be
delivered to Seller not later than two days after the Termination Date.


                            ARTICLE 10. MISCELLANEOUS

               Section  10.1   Amendments.   Subject  to  applicable  law,  this
                               ----------
Agreement and any exhibit or schedule attached hereto may be amended at any time
prior to the  Closing  Date by an  instrument  in writing  duly  signed by or on
behalf of each of the parties hereto.


             Section 10.2  Further Instruments and Assurances.   At  or prior to
                           ----------------------------------
and after the Closing, each party shall from time to time, at the request of any
other party and without further cost or expense to such other party, execute and
deliver  such  other  instruments  and  take  such  other  actions  as  shall be
reasonably  required by any other party in order to carry out the  transactions,
agreements and covenants contained in or contemplated by this Agreement.

             Section 10.3 Public Announcements.  Press releases and other public
                          --------------------
communications  of any  sort  relating  to this  Agreement  or the  transactions
contemplated hereby shall be subject to the prior written consent of all parties
to this Agreement as to the contents of any such public disclosure, such consent
not being unreasonably withheld, conditioned or delayed; provided, however, each
party  hereto  shall be entitled  to make any  disclosure  as is required  under
applicable law, subpoena or final,  nonappealable court order, in the reasonable
judgment of such disclosing party.

            Section 10.4  Governing  Law. THIS AGREEMENT AND THE LEGAL RELATIONS
                          --------------
BETWEEN THE PARTIES SHALL BE GOVERNED BY AND  CONSTRUED IN  ACCORDANCE  WITH THE
LAWS OF THE  STATE OF NEW  YORK,  WITHOUT  REFERENCE  TO THE  CONFLICTS  OF LAWS
PROVISIONS THEREOF.

             Section 10.5 Notices. All communications under this Agreement shall
                          -------  
be in  writing  and shall be  deemed to have been duly  given (i) on the date of
receipt  if  served  personally  or by  confirmed  facsimile  or  other  similar
communication,  (ii) on the first day after sending if sent for guaranteed  next
day delivery by a next-day  courier  service or (iii) on the fourth Business Day
after mailing if mailed to the party or parties to whom notice is to be given by
registered or certified mail,  return receipt  requested,  postage prepaid,  and
properly addressed as follows:

             If to Purchaser:

                      American Mobile Satellite Corporation
                      10802 Parkridge Boulevard
                      Reston, Virginia  20191-5416
                      Attention:  General Counsel
                      Facsimile:  (703) 758-6134

                      and

                      American Mobile Satellite Corporation
                      10802 Parkridge Boulevard
                      Reston, Virginia  20191-5416
                      Attention:  Chief Executive Officer
                      Facsimile:  (703) 758-6106


             With a copy to:

                      Arnold & Porter
                      555 12th Street, N.W.
                      Washington, D.C. 20004
                      Attention:  Samuel A. Flax, Esq.
                      Facsimile:  (202) 942-5999

             If to Seller:

                      Motorola, Inc.
                      1303 East Algonquin Road
                      Schaumburg, Illinois 60196
                      Attention:  General Counsel
                      Facsimile:  (847) 576-3628

             With a copy to:

                      Kirkland & Ellis
                      200 East Randolph Drive
                      Chicago, Illinois 60601
                      Attention:  Mark B. Tresnowski
                      Facsimile:  (312) 861-2200

Any party may change its address for purposes of this Section 10.5 by giving the
other parties hereto notice of the new address in the manner set forth above.

              Section 10.6  Assignment and Binding  Effect.  This  Agreement may
                            ------------------------------
not be assigned by any party  hereto  without the prior  written  consent of the
other parties. Subject to the foregoing, all of the terms and provisions of this
Agreement  shall be binding upon and inure to the benefit of and be  enforceable
by the successors and assigns of the parties hereto.


              Section 10.7  Entire Agreement.  This  Agreement, the exhibits and
                            ----------------
schedules hereto,  the Disclosure  Schedule dated as of even date herewith,  and
other documents  delivered  pursuant hereto,  referred to herein or executed and
delivered in connection with the transactions  contemplated hereby,  contain the
entire  agreement  among  Purchaser,  Seller,  MAA and MAI with  respect  to the
transactions  contemplated herein and, except as provided herein,  supersede all
previous negotiations, commitments and writings.

              Section 10.8  Severability.  Whenever  possible, each provision of
                            ------------
this  Agreement  will be interpreted in such manner as to be effective and valid
under  applicable  law,  but if any  provision  of this  Agreement is held to be
prohibited  by  or  invalid  under   applicable  law,  such  provision  will  be
ineffective  only to the  extent  of such  prohibition  or  invalidity,  without
invalidating the remainder of such provision or the remaining provisions of this
Agreement.


              Section 10.9  Counterparts.  This  Agreement  may  be executed and
                            ------------
delivered  in two or more  counterparts,  each  of  which  shall  be  deemed  an
original.
 

              Section 10.10  No  Third  Party  Beneficiaries.  Nothing  in  this
                             -------------------------------
Agreement  is  intended  to confer any rights or  remedies,  whether  express or
implied,  under or by reason of this  Agreement,  on any persons  other than the
parties hereto and their respective  successors and assigns,  nor is anything in
this  Agreement  intended to relieve or discharge the obligation or liability of
any third persons to any party to this Agreement. Notwithstanding the preceding,
any other provision  herein or in any Collateral  Agreement,  Purchaser and AMSC
shall be entitled to assign this Agreement, to third party lenders as collateral
for their loans from such entities.

             Section 10.11 Delays or Omissions. No delay or omission to exercise
                           -------------------
any right, power or remedy accruing to Purchaser, AMSC or Seller upon any breach
or default of Purchaser,  AMSC or Seller,  respectively,  under this  Agreement,
shall  impair  any such  right,  power or remedy  of such  party nor shall it be
construed  to be a waiver of any such  breach  or  default,  or an  acquiescence
therein, or in any similar breach or default thereafter occurring; nor shall any
waiver of any single breach or default be deemed a waiver of any other breach or
default theretofore or thereafter occurring.

             Section 10.12  Construction.  This  Agreement  is  to  be deemed to
                            ------------
have been prepared jointly by the parties hereto after arms length negotiations,
and any  uncertainty  or  ambiguity  existing  herein  shall not be  interpreted
against  any  party,   but  according  to  the   application  of  the  rules  of
interpretation of contracts.


             Section 10.13  Knowledge Standard.  The term "knowledge," "best  of
                            ------------------ 
knowledge," "know" and any similar term when used with respect to Seller, MAA or
MAI means actual (and not  constructive)  knowledge of any director,  officer or
employee of Seller or an Affiliate of Seller,  including but not limited to MAA,
MAI and the Subsidiaries.



             Section 10.14 Expenses.  Except as otherwise  provided herein,  all
                           --------
costs,  fees and expenses  incurred in connection  with this Agreement  shall be
paid by the party  incurring such cost, fee or expense,  except that filing fees
related to the FCC Consents shall be shared jointly by Seller and Purchaser. All
costs  and  expenses  of MAA,  MAI  and the  Subsidiaries  associated  with  the
negotiation,  execution,  delivery and  consummation  of the Agreement  shall be
deemed to be the  responsibility  of Seller and at or before the Closing Sellers
shall reimburse MAA, MAI and the Subsidiaries therefor.














             IN WITNESS  WHEREOF,  each of Seller,  MAA, MAI, AMSC and Purchaser
has caused this  Agreement to be duly executed on its behalf,  as of the day and
year first above written.

                                           MOTOROLA, INC.


                                           By:/s/James G. Roseland
                                                 -----------------
                                              Name:  James G. Roseland
                                                     -----------------
                                              Title: Vice President
                                                     --------------


                                           MOTOROLA ARDIS ACQUISITION, INC.


                                           By:/s/James G. Roseland
                                                 -----------------
                                              Name:  James G. Roseland
                                                     -----------------
                                              Title: Vice President
                                                     --------------



                                           MOTOROLA ARDIS, INC.


                                           By:/s/Theodore W. Schaffner
                                                 ---------------------
                                              Name:  Theodore W. Schaffner
                                                     ---------------------
                                              Title:  Corporate Vice President 
                                                       and Director of Business 
                                                       Development
                                                      --------------------------


                                           AMERICAN MOBILE SATELLITE CORPORATION


                                           By:/s/Gary M. Parsons
                                                 ---------------
                                              Name:  Gary M. Parsons
                                                     ---------------
                                              Title:  CEO and President
                                                      -----------------















                                           AMSC ACQUISITION COMPANY, INC.



                                           By:/s/Gary M. Parsons
                                                 ---------------
                                              Name:  Gary M. Parsons
                                                     ---------------
                                              Title:  CEO and President
                                                      -----------------



                                   EXHIBIT A

THIS  SECURITY HAS NOT BEEN  REGISTERED  UNDER THE  SECURITIES  ACT OF 1933,  AS
AMENDED,  OR ANY STATE SECURITIES LAWS AND MAY NOT BE TRANSFERRED OR SOLD EXCEPT
IN COMPLIANCE THEREWITH OR PURSUANT TO AN EXEMPTION THEREFROM.


                               AMERICAN MOBILE SATELLITE CORPORATION


                               Warrant for the Purchase of Shares of
                       Common Stock of American Mobile Satellite Corporation

No. ___                                                      Warrant to Purchase
                                                            ____________  Shares

             FOR  VALUE  RECEIVED,  AMERICAN  MOBILE  SATELLITE  CORPORATION,  a
Delaware corporation (the "Company"),  hereby certifies that MOTOROLA, INC., its
successor  or  permitted  assigns (the  "Holder"),  is entitled,  subject to the
provisions of this Warrant, to purchase from the Company, at the times specified
herein,  _______________  (___________)  (the "Warrant Share Amount") fully paid
and  non-assessable  shares of Common Stock of the  Company,  par value $.01 per
share (the "Common Stock"),  at a purchase price per share equal to the Exercise
Price (as hereinafter defined).  The Warrant Share Amount and the Exercise Price
are subject to adjustment from time to time as hereinafter set forth.

                    1.  DEFINITIONS.  The following terms, as used herein,  have
the following meanings:

             "Accepted Alien Ownership  Percentage  Limitation" means 24.99% or,
in the event of a modification of the Alien Ownership Restrictions subsequent to
the date hereof,  such percentage  limitation upon the Company's Alien ownership
as may










be in effect from time to time as a result of such modification, less 0.01%.

             "Alien" means any alien or a representative  thereof,  or a foreign
              -----
government  or a  representative  thereof,  or a  corporation  or  other  entity
organized under the laws of any foreign government.

             "Alien Ownership Percentage" means, with respect to any Person, the
              -------------------------- 
percentage  of total  ownership in such Person  owned of record,  as well as the
percentage of total ownership in such Person voted, by Aliens; provided, that if
under the Alien  Ownership  Restrictions  such Person  would be deemed to have a
percentage of total  ownership owned of record or voted by Aliens other than the
actual  percentage  so  owned or  voted,  then  such  Person's  Alien  Ownership
Percentage shall be such deemed percentage.

             "Alien  Ownership   Restrictions"   means  Section  310(b)  of  the
              ------------------------------- 
Communications  Act, as modified by any  interpretation,  ruling or order of the
Federal  Communications  Commission (or any successor agency)  applicable to the
Company or any of its subsidiaries.

             "AMSC" means AMSC Acquisition Company, Inc., a Delaware corporation
              ----
and a wholly-owned subsidiary of the Company.

             "Board of Directors" means the Board of Directors of the Company.
              ------------------

             "Business Day" means any day except a Saturday, Sunday or other day
              ------------
on which  commercial  banks in the  City of New  York are  authorized  by law to
close.

             "Closing Price" has the meaning set forth in Section 10.D.
              -------------

             "Common Stock" has the meaning set forth in the preamble hereof.
              ------------

             "Communications  Act"  means  the  Communications  Act  of 1934, as
              -------------------
amended, or any successor statute.

             "Company" has the meaning set forth in the preamble hereof.
              -------

             "Constituent Person" has the meaning set forth in Section 11.
              ------------------

             "Current Market Price Per  Common Share" has  the meaning set forth
              --------------------------------------
in Section 10.D.

             "Exercise  Date"  means the  applicable  date of  exercise  of this
              --------------
Warrant, as indicated on the Warrant Exercise Notice delivered by the Holder.

             "Exercise  Price"  means  initially  $0.01 per  Warrant  Share,  as
              ---------------
adjusted from time to time.

             "Exercising Holder" has the meaning set forth in Section 3.A.
              -----------------

             "Expiration Date" means ______ __, 200_, at 5:00 p.m. New York City
              ---------------
 time.

             "FCC"  means  the  Federal  Communications   Commission,   or  such
              ---
successor agency of the Federal government with responsibility for administering
the Communications Act.

             "MAA" means Motorola ARDIS Acquisition, Inc.
              ---

             "MAI" means Motorola ARDIS, Inc.
              ---

             "NASDAQ" means the  National Market  of the National Association of
              ------
Securities Dealers, Inc. Automated Quotation System.

             "NASD Limit" has the meaning set forth in Section 4.
              ----------

             "NYSE" means the New York Stock Exchange Inc.
              ----

             "Non-Electing Share" has the meaning set forth in Section 11.
              ------------------

             "Person" means an  individual,  corporation,  partnership,  limited
              ------
liability  company,  association,  trust or any  other  entity  or  organization
including a government or political  subdivision or an agency or instrumentality
thereof.

             "Registration  Rights  Agreement"  has  the  meaning  set  forth in
              -------------------------------    
Section 16.

             "Securities Act" means the Securities Act of 1933, as amended,  and
              --------------
the rules and regulations promulgated thereunder.

             "Stock Purchase  Agreement"  means the Stock Purchase  Agreement by
              -------------------------
and among the Company,  AMSC, the Holder, MAA and MAI, dated as of December ___,
1998.

             "Warrant Exercise Notice" means the Warrant Exercise Notice forming
              -----------------------
a part hereof.

             "Warrant  Margin"  means,  on any date,  the  difference of (x) the
              ---------------
greater of (A) the average of the Closing Prices (as defined in Section 10.D) on
each of the 20 trading days immediately  preceding such date and (B) the Closing
Price [on the  trading  days]  prior to the such  date,  minus (y) the  Exercise
Price.

             "Warrant Share  Amount"  has the  meaning set forth in the preamble
              ---------------------
hereof.

             "Warrant Shares" means the shares of Common Stock  deliverable upon
              --------------
exercise of this Warrant, as adjusted from time to time.

                    2. EXERCISE OF WARRANT.

                    A.  Subject to Section 15 hereof,  the Holder is entitled to
exercise  this Warrant in whole or in part at any time, or from time to time, to
and including the Expiration Date or, if such day is not a Business Day, then on
the next  succeeding day that shall be a Business Day. To exercise this Warrant,
the Holder shall  execute and deliver to the Company at its address set forth in
Section 12 hereof a Warrant  Exercise Notice  substantially  in the form annexed
hereto and shall deliver to the Company (x) this Warrant,  including the Warrant
Exercise  Subscription  Form forming a part hereof duly  executed by the Holder,
and (y) subject to Section 2.B, payment of the Exercise Price then in effect for
such Warrant Shares. Upon such delivery and payment,  the Holder shall be deemed
to be the  holder of record of the  Warrant  Shares  subject  to such  exercise,
notwithstanding  that the stock  transfer  books of the  Company  shall  then be
closed or that  certificates  representing such Warrant Shares shalL not then be
actually delivered to the Holder.

                    B. The Exercise Price may be paid in cash or by certified or
official bank check or bank cashier's  check payable to the order of the Company
or by wire transfer of immediately  available funds to an account  designated by
the  Company or by  cancellation  of  indebtedness  owed to the Holder or by any
combination  of such methods.  In the  alternative,  the Holder may exercise its
right to  receive  Warrant  Shares (i) on a net basis,  such that,  without  the
exchange of any funds,  the Holder will  receive  that number of Warrant  Shares
(and such other consideration)  otherwise issuable (or payable) upon exercise of
this Warrant  less that number of Warrant  Shares  having an  aggregate  Current
Market  Price Per  Common  Share on the  Exercise  Date  equal to the  aggregate
Exercise Price that would otherwise have been paid by the Holder for the Warrant
Shares or (ii) delivery to the Company,  together with appropriate stock powers,
of  certificates  evidencing  shares of Common Stock having an aggregate Current
Market  Price  Per  Common  Share  on the  Exercise  Date of not  less  than the
aggregate  Exercise Price. The Company shall pay any and all documentary,  stamp
or similar  issue or transfer  taxes payable in respect of the issue or delivery
of this Warrant and the issue and delivery of the Warrant Shares.

                    C. If the  Holder  exercises  this  Warrant  in  part,  this
Warrant shall be  surrendered  by the Holder to the Company and a new Warrant of
the same  tenor  and for the  unexercised  number  of  Warrant  Shares  shall be
executed by the Company.  The Company shall register the new Warrant in the name
of the Holder or in such name or names of its transferee(s)  pursuant to Section
8 hereof as may be directed in writing by the Holder and deliver the new Warrant
to the Person or Persons entitled to receive the same.

                    D. Except as otherwise provided in Section 3, upon surrender
of this Warrant in conformity with the foregoing  provisions,  the Company shall
transfer to the Holder of this Warrant appropriate  evidence of ownership of the
shares of Common Stock or other securities or property  (including any money) to
which the Holder is entitled,  registered or otherwise  placed in, or payable to
the order of,  the name or names of the  Holder or its  transferee(s)  as may be
directed in writing by the Holder,  and shall deliver such evidence of ownership
and any other  securities  or  property  (including  any money) to the Person or
Persons entitled to receive the same, together with an amount in cash in lieu of
any fraction of a share as provided in Section 7 below.

                    3. OWNERSHIP LIMITATION.  If at any time the exercise of any
Warrants  pursuant  to  Section 2 would  cause  the  Company's  Alien  Ownership
Percentage to exceed the Accepted Alien Ownership Percentage Limitation, then in
lieu of issuing shares of Common Stock pursuant to Section 2:

                    A.  the  Company  shall  issue  to  each  Holder  exercising
               Warrants at such time (each an  "Exercising  Holder") whose Alien
                                                ------------------
               Ownership  Percentage is less than or equal to the Accepted Alien
               Ownership  Percentage  Limitation  the number of shares of Common
               Stock to which such  Exercising  Holder is  entitled  pursuant to
               Section 2;

                    B. the Company shall issue to each  Exercising  Holder whose
               Alien  Ownership  Percentage  is greater than the Accepted  Alien
               Ownership  Percentage  Limitation (each, an "Affected  Exercising
               Holder") a number of shares of Common Stock equal to the quotient
               of (x) the  product of (A) the  number of shares of Common  Stock
               that,  immediately after giving effect to any issuances of Common
               Stock pursuant to the foregoing Section 3.A, could be issued to a
               Person with a 100% Alien Ownership Percentage without causing the
               Company's Alien Ownership Percentage to exceed the Accepted Alien
               Ownership Percentage Limitation,  multiplied by (B) the number of
               shares of Common Stock to which such Affected  Exercising  Holder
               would be entitled  pursuant to Section 2 but for the  application
               of  this  Section  3,  divided  by (y)  the  product  of (A)  the
               aggregate  number of shares of Common Stock to which all Affected
               Exercising  Holders  would be entitled  pursuant to Section 2 but
               for the  application  o this  Section 3,  multiplied  by (B) such
               Affected Exercising Holder's Alien Ownership Percentage; provided
               that in no event  shall the  number  of  shares  of Common  Stock
               issuable  to any  Affected  Exercising  Holder  pursuant  to this
               Section 3.B exceed the number of shares of Common  Stock to which
               such Affected Exercising Holder would have been entitled pursuant
               to Section 2 but for the application of this Section 3; and

                    C. the Company shall deliver by wire transfer of immediately
               available funds to the account of each Affected Exercising Holder
               specified in such Affected  Exercising  Holder's Warrant Exercise
               Notice,  an  amount  equal to the  product  of (x) the  number of
               shares of Common Stock to which such Affected  Exercising  Holder
               would  have  been  entitled  pursuant  to  Section 2 that are not
               issuable  to such  Affected  Exercising  Holder  pursuant  to the
               foregoing  Section 3.B,  multiplied by (y) the Warrant  Margin on
               the Exercise Date.

                    4. RESTRICTIVE LEGEND.  Upon original issuance thereof,  and
until such time at the same shall have been registered  under the Securities Act
or sold  pursuant to Rule 144  promulgated  thereunder  (or any similar  rule or
regulation),  each Warrant and any certificates  evidencing Warrant Shares shall
bear a legend  substantially  in the form of the  legend  set forth on the first
page hereof,  unless in the opinion of counsel  reasonably  satisfactory  to the
Company, such legend is no longer required by the Securities Act.

                    5. RESERVATION OF SHARES.  The Company hereby agrees that at
all times it shall  reserve for  issuance  and  delivery  upon  exercise of this
Warrant such number of its  authorized  but  unissued  shares of Common Stock as
will be  sufficient  to permit the  exercise in full of this  Warrant.  All such
shares shall be duly  authorized  and, when issued upon such exercise,  shall be
validly  issued,  fully  paid and  non-assessable,  free and clear of all liens,
security  interests,  charges and other  encumbrances  or  restrictions  on sale
(other than general regulatory  restrictions  under the Communications  Act) and
free and clear of all preemptive rights.

                    6.  FRACTIONAL   SHARES.   No  fractional  shares  or  scrip
representing fractional shares shall be issued upon the exercise of this Warrant
and in lieu of delivery of any such fractional  share upon any exercise  hereof,
the  Company  shall pay to the Holder an amount in cash  equal to such  fraction
multiplied by the Current Market Price Per Common Share on the Exercise Date.

                    7. EXCHANGE, TRANSFER OR ASSIGNMENT OF WARRANT.

                    A. The Company shall from time to time register the exchange
               or transfer of any outstanding  Warrant in a Warrant  register to
               be maintained by the Company upon surrender  thereof  accompanied
               by a  written  instrument  or  instruments  of  transfer  in form
               satisfactory  to the  Company,  duly  executed by the  registered
               Holder  or  Holders  thereof  or  by  the  duly  appointed  legal
               representative  thereof or by a duly  authorized  attorney.  Each
               taker and holder of this  Warrant by taking or holding  the same,
               consents  and agrees  that the  registered  holder  hereof may be
               treated by the Company and all other  Persons  dealing  with this
               Warrant as the  absolute  owner hereof for any purpose and as the
               Person entitled to exercise the rights represented hereby.

                    B. Prior to any  proposed  transfer  of the  Warrants or the
               Warrant  Shares,  unless  such  transfer  is made  pursuant to an
               effective  registration  statement  under the  Securities Act the
               Holder  will  deliver  to the  Company,  if so  requested  by the
               Company,  an opinion of counsel  reasonably  satisfactory in form
               and substance to the Company,  to the effect that the Warrants or
               Warrant  Shares,   as  applicable,   may  be  sold  or  otherwise
               transferred  without   registration  under  the  Securities  Act.
               Subject to the  preceding  sentence,  the Holder of this  Warrant
               shall be entitled,  without obtaining the consent of the Company,
               to assign and transfer this Warrant, at any time in whole or from
               time to time in part,  to any Person or  Persons.  Subject to the
               foregoing,  upon  surrender  of  this  Warrant  to  the  Company,
               together with the attached Warrant Assignment Form duly executed,
               the  Company  shall,  without  charge,  execute and deliver a new
               Warrant in the name of the  assignee or  assignees  named in such
               instrument of assignment  and, if the Holder's entire interest is
               not being assigned,  in the name of the Holder,  and this Warrant
               shall promptly be cancelled.

                    8. LOSS OR  DESTRUCTION  OF  WARRANT.  Upon  receipt  by the
Company  of  evidence  satisfactory  to it (in the  exercise  of its  reasonable
discretion) of the loss, theft,  destruction or mutilation of this Warrant,  and
(if  requested  by the  Company in the case of loss,  theft or  destruction)  of
reasonably satisfactory indemnification,  and upon surrender and cancellation of
this Warrant, if mutilated,  the Company shall execute and deliver a new Warrant
of like tenor and date  representing the right to purchase an equivalent  number
of Warrant Shares.

                    9. ANTI-DILUTION PROVISIONS.

                    A. In case the  Company  shall at any  time  after  the date
               hereof (i)  declare a dividend or make a  distribution  on Common
               Stock  payable in Common Stock or other  shares of the  Company's
               capital   stock,   (ii)   subdivide,   split  or  reclassify  the
               outstanding  Common Stock into a larger  number of shares,  (iii)
               combine or reclassify the outstanding Common Stock into a smaller
               number of shares,  or (iv) issue any shares of its capital  stock
               in  a  reclassification  of  Common  Stock  (including  any  such
               reclassification  in connection with a consolidation or merger in
               which the Company is the  continuing  corporation),  then in each
               such case the Warrant Share Amount shall be adjusted to equal the
               number of shares to which the holder of this  Warrant  would have
               been entitled  upon the  occurrence of such event if this Warrant
               had  been  exercised   immediately   prior  to  such  time.  Such
               adjustment shall be made  successively  whenever any event listed
               above shall occur.

                    B. In case  the  Company  shall  fix a  record  date for the
               making of a  distribution  to holders of Common Stock  (including
               any such  distribution made in connection with a consolidation or
               merger in which the  Company is the  continuing  corporation)  of
               evidences of  indebtedness,  assets or other property  (excluding
               cash dividends, other cash distributions from current or retained
               earnings  or  dividends  payable  in  Common  Stock  for which an
               adjustment  has been made pursuant to Section  9.A),  the Warrant
               Share  Amount to be in effect  after  such  record  date shall be
               determined  by  multiplying  the Warrant  Share  Amount in effect
               immediately  prior  to  such  record  date  by  a  fraction,  the
               numerator  of which shall be the Current  Market Price Per Common
               Share,  and the denominator of which shall be such Current Market
               Price Per Common Share on such record date,  less the fair market
               value  (determined  by the  Board of  Directors  of the  Company;
               provided   that  if  the   Holder   shall   object  to  any  such
               determination, the Board of Directors shall retain an independent
               appraiser reasonably satisfactory to the Holder to determine such
               fair market value) of the portion of the assets,  other  property
               or  evidence  of  indebtedness  so to  be  distributed  which  is
               applicable to one share of Common Stock.  Such adjustments  shall
               be made successively whenever such a record date is fixed; and in
               the event  that such  distribution  is not so made,  the  Warrant
               Share  Amount  shall again be  adjusted  to be the Warrant  Share
               Amount  which would then be in effect if such record date had not
               been fixed.

                    C. If as a result of any event or for any other reason,  any
               adjustment is made which increases the number of shares of Common
               Stock  issuable upon  conversion,  exercise or exchange of, or in
               the conversion or exercise price or exchange ratio applicable to,
               any  outstanding  securities of the Company that are  convertible
               into, or exercisable  or  exchangeable  for,  Common Stock of the
               Company, then a corresponding  adjustment shall be made hereunder
               to increase the Warrant Share Amount, but only to the extent that
               no such  adjustment  has been made  pursuant  to Section 9.A or B
               hereof with respect to such event or for such other reason.

                    D. For the  purpose of any  computation  under  Section 3 or
               Section 9.B hereof, on any determination date the "Current Market
                                                                  --------------
               Price  Per  Common  Share"  shall  be  deemed  to be the  average
               -------------------------
               (weighted  by daily  trading  volume) of the  Closing  Prices (as
               defined  below) per share of Common Stock for the 20  consecutive
               trading  days  immediately  prior to such date.  "Closing  Price"
               means (1) if shares of Common Stock then are listed and traded on
               the    NYSE,    the    closing    price    on    such    day   as
               reported, on the NYSE Composite  Transactions Tape; (2) if shares
               of Common  Stock then are not listed and traded on the NYSE,  the
               closing price on such day as reported by the  principal  national
               securities  exchange  on which the shares are listed and  traded;
               (3) if shares of Common  Stock  then are not listed and traded on
               any such  securities  exchange,  the last  reported sale price on
               such day on the NASDAQ; or (4) if shares of Common Stock then are
               not  traded on the NASDAQ  National  Market,  the  average of the
               highest  reported bid and lowest reported asked price on such day
               as reported  by NASDAQ.  If on any  determination  date shares of
               Common Stock are not quoted by any such organization, the Current
               Market  Price Per Common  Share shall be the fair market value of
               such shares on such determination  date as reasonably  determined
               by the Board of  Directors.  If the  Holder  shall  object to any
               determination  by the Board of  Directors  of the Current  Market
               Price Per Common Share, the Current Market Price Per Common Share
               shall be the fair  market  value  per  share of  Common  Stock as
               determined by an independent appraiser retained by the Company at
               its expense and reasonably acceptable to the Holder. For purposes
               of any computation  under this Section 9, the number of shares of
               Common  Stock  outstanding  at any given time  shall not  include
               shares owned or held by or for the account of the Company.

                    E. No adjustment in the Warrant Share Amount or the Exercise
               Price shall be required unless such  adjustment  would require an
               increase  or  decrease  of at least one  percent of such  amount;
               provided that any adjustments which by reason of this Section 9.F
               are not  required  to be made shall be carried  forward and taken
               into account in any subsequent adjustment. All calculations under
               this  Section 9 shall be made to the  nearest one tenth of a cent
               or to the nearest  hundredth of a share as the case may be.

                    G.  In the  event  that,  at any  time  as a  result  of the
               provisions  of this  Section 9, the holder of this  Warrant  upon
               subsequent  exercise shall become  entitled to receive any shares
               of capital  stock of the  Company  other than Common  Stock,  the
               number of such other shares so  receivable  upon exercise of this
               Warrant shall  thereafter  be subject to adjustment  from time to
               time in a manner and on terms as nearly equivalent as practicable
               to the provisions contained herein.

                    H.  Upon any  adjustment  pursuant  to this  Section  9, the
               Company shall promptly  thereafter (i) cause to be filed with the
               Company a certificate of an officer of the Company  setting forth
               the Warrant Share Amount and Exercise Price after such adjustment
               and setting forth in reasonable  detail the method of calculation
               and the facts upon which such  calculations  are based,  and (ii)
               cause to be given to each  registered  Holder of this  Warrant at
               the  address as set forth in  Section  11 written  notice of such
               adjustments.  Where  appropriate,  such  notice  may be  given in
               advance  and  included  as a part of the  notice  required  to be
               delivered pursuant to Section 12.B.

                    10.  REORGANIZATION,   CONSOLIDATION,  MERGER,  OR  SALE  OF
ASSETS.  In  case  of any  reclassification,  redesignation,  reorganization  of
recapitalization  by the  Company  (other  than as set  forth in  Section  9) or
consolidation  of the Company  with,  or merger of the Company  into,  any other
Person, any merger of another Person into the Company (other than a merger which
does not result in any reclassification, conversion, exchange or cancellation of
outstanding shares of Common Stock) or any sale or transfer of all substantially
all of the assets of the Company or of the Person  formed by such  consolidation
or resulting from such merger or which acquires such assets, as the case may be,
the Holder shall have the right thereafter to exercise this Warrant for the kind
and  amount  of  securities,  cash  and  other  property  receivable  upon  such
reclassification,      redesignation,     reorganization,      recapitalization,
consolidation,  merger,  sale or transfer by a holder of the number of shares of
Common Stock for which this Warrant may have been exercised in full  immediately
prior to such reclassification, redesignation, reorganization, recapitalization,
consolidation,  merger,  sale or  transfer,  assuming  (i) such holder of Common
Stock is not a Person  with  which the  Company  consolidated  or into which the
Company  merged  or which  merged  into the  Company  or to which  such  sale or
transfer was made, as the case may be ("Constituent Person"), or an Affiliate of
a Constituent  Person and (ii) in the case of a consolidation,  merger,  sale or
transfer  which includes an election as to the  consideration  to be received by
the  holders,  such  holder of Common  Stock  failed to  exercise  its rights of
election,  as to the kind or  amount  of  securities,  cash and  other  property
receivable upon such  consolidation,  merger, sale or transfer (provided that if
the kind or amount of securities,  cash and other property  receivable upon such
consolidation, merger, sale or transfer is not the same for each share of Common
Stock held immediately prior to such consolidation,  merger, sale or transfer by
other than a Constituent  Person or an Affiliate thereof and in respect of which
such rights of election  shall not have been exercised  ("Non-electing  share"),
then for the purpose of this Section 10 the kind and amount of securities,  cash
and other property receivable upon such consolidation,  merger, sale or transfer
by each  Non-electing  share  shall  be  deemed  to be the kind  and  amount  so
receivable per share by a plurality of the Non-electing shares.  Adjustments for
events subsequent to the effective date of such reclassification, redesignation,
reorganization, recapitalization, consolidation, merger and sale of assets shall
be as nearly equivalent as may be practicable to the adjustments provided for in
this  Warrant.  In any such  event,  effective  provisions  shall be made in the
certificate  or  articles  of   incorporation  of  the  resulting  or  surviving
corporation,  in any  contract  of  sale,  conveyance,  lease  or  transfer,  or
otherwise  so that the  provision  set forth  herein for the  protection  of the
rights of the Holder shall  thereafter  continue to be applicable;  and any such
resulting or surviving  corporation  shall  expressly  assume the  obligation to
deliver,  upon  exercise,  such  shares of  stock,  other  securities,  cash and
property.  The provisions of this Section 11 shall similarly apply to successive
consolidations, mergers, sales, leases or transfers.

                    11. NOTICES.  Any notice,  demand or delivery  authorized or
required by this Warrant shall be in writing and shall be given to the Holder or
the Company, as the case may be, at its address (or telecopier number) set forth
below, or such other address (or telecopier number) as shall have been furnished
to the party giving or making such notice, demand or delivery:

             If to the Company:

                      American Mobile Satellite Corporation
                      10802 Parkridge Blvd.
                      Reston, VA  22091
                      Telecopy:  (703) 758-6134
                      Attention:    Randy Segal,
                                    General Counsel

             With a copy to:

                      Arnold & Porter
                      555 - 12th Street, N.W.
                      Washington, D.C.  20004
                      Telecopy: (202) 942-5999
                      Attention:    Samuel A. Flax, Esq.

             If to the Holder:

                      Motorola, Inc.
                      Law Department, IL01/11
                      1303 E. Algonquin Road
                      Schaumburg, IL  60196
                      Telecopy: (847) 576-3628
                      Attention:    Linda Valentine,
                                    Corporate Vice President and General Counsel

             With a copy to:

                      Kirkland & Ellis
                      200 E. Randolph Avenue
                      Chicago, IL  60601
                      Telecopy: (312) 861-2200
                      Attention:    Mark Tresnowski, Esq.

Each  such  notice,  demand  or  delivery  shall  be  effective  (i) if given by
telecopy,  when such telecopy is  transmitted to the telecopy  number  specified
herein and the intended  recipient confirms the receipt of such telecopy or (ii)
if given by any other means, when received at the address specified herein.

                    12. NOTICES TO WARRANT HOLDERS.

                    A. The Company shall  provide to the Holder,  at its address
               and in the manner set forth in Section 12, a notice of expiration
               of this  Warrant not less than 90 nor more than 120 days prior to
               the Expiration Date.

                    B. In the event:

                         (a) the Company shall authorize the issuance to holders
                    of shares of Common Stock of rights,  options or warrants to
                    subscribe  for or purchase  shares of Common Stock or of any
                    other subscription rights or warrants; or

                         (b) the Company  shall  authorize the  distribution  to
                    holders of shares of Common Stock of assets, including cash,
                    evidences of its indebtedness, or other securities; or

                         (c) of any  reorganization,  consolidation or merger to
                    which the  Company is a party and for which  approval of any
                    shareholders   of  the  Company  is  required,   or  of  the
                    conveyance or transfer of the  properties  and assets of the
                    Company   substantially   as  an   entirety,   or   of   any
                    reclassification  or change of Common  Stock  issuable  upon
                    exercise  of the  Warrants,  or a tender  offer or  exchange
                    offer for shares of Common Stock; or

                         (d)  of  the  voluntary  or  involuntary   dissolution,
                    liquidation or winding up of the Company; or




                                      - 2 -



                         (e) the Company  proposes to take any action that would
                    require an  adjustment  to the Warrant  Share  Amount or the
                    Exercise Price pursuant to Section 10 hereof;

then the  Company  shall  cause to be given  to the  registered  Holder  of this
Warrant,  at  least 20 days  prior to the  applicable  record  date  hereinafter
specified,  or 20 days  prior to the date of the event in the case of events for
which there is no record date a written  notice stating (i) the date as of which
the  holders of record of shares of Common  Stock  entitled  to receive any such
rights,  options,  warrants or  distribution  are to be determined,  or (ii) the
initial  expiration  date set forth in any tender  offer or  exchange  offer for
shares of  Common  Stock,  or (iii)  the date on which any such  reorganization,
reclassification,  consolidation,  merger,  conveyance,  transfer,  dissolution,
liquidation or winding up is expected to become  effective or  consummated,  and
the date as of which it is expected  that  holders of record of shares of Common
Stock  shall be  entitled  to  exchange  such  shares  for  securities  or other
property,  if  any,  deliverable  upon  such  reorganization,  reclassification,
consolidation, merger, conveyance, transfer, dissolution, liquidation or winding
up. The failure to give the notice  required by this  Section 13.B or any defect
therein  shall not affect the legality or validity of any  distribution,  right,
option,  warrant,  consolidation,  merger,  conveyance,  transfer,  dissolution,
liquidation or winding up, or the vote upon any action.

                         13. RIGHTS OF THE HOLDER.  Prior to the exercise of any
Warrant,  the Holder shall not, by virtue hereof, be entitled to any rights of a
stockholder of the Company, including, without limitation, the right to vote, to
receive dividends or other distributions, to exercise any preemptive right or to
receive any notice of meetings of  stockholders or any notice of any proceedings
of the  Company  except as may be  specifically  provided  for  herein.  Nothing
contained  herein  shall  impose any  obligation  on the Holder to purchase  any
securities  or impose any  liabilities  on such Holder as a  stockholder  of the
Company,  whether such  obligation or liabilities are asserted by the Company or
by creditors of the Company.

                         14. LIMITATION ON EXERCISE OF WARRANT;  CANCELLATION OF
WARRANTS. Notwithstanding anything to the contrary in this Warrant, this Warrant
shall be  exercisable  at any given time only for the  number of Warrant  Shares
which is equal to the applicable  Warrant Share Amount as in effect from time to
time.

                         15. REGISTRATION  RIGHTS. The Holder of this Warrant is
entitled  to certain  registration  rights with  respect to the  Warrant  Shares
issuable upon the exercise thereof.  Said registration rights are set forth in a
Registration  Rights  Agreement  dated as of December __, 1997, by and among the
Company and the Holder (the "Registration  Rights Agreement").  By acceptance of
this Warrant,  the Holder  hereof agrees that upon exercise of this Warrant,  in
whole or in part, such Holder will be bound by the Registration Rights Agreement
as a holder of Registrable Securities  thereunder.  The Company agrees that upon
transfer of this Warrant, in whole or in part, pursuant to Section 7 hereof, the
transferee  shall be  entitled  to  become a party  to the  Registration  Rights
Agreement  if not already a party  thereto.  A copy of the  Registration  Rights
Agreement  may be obtained  by the Holder  hereof  upon  written  request to the
Company.

                         16.  GOVERNING  LAW  AND  WAIVER  OF JURY  TRIAL.  THIS
WARRANT AND ALL RIGHTS  ARISING  HEREUNDER  SHALL BE CONSTRUED AND DETERMINED IN
ACCORDANCE  WITH THE INTERNAL LAWS OF THE STATE OF NEW YORK, AND THE PERFORMANCE
THEREOF SHALL BE GOVERNED AND ENFORCED IN ACCORDANCE WITH SUCH LAWS. THE PARTIES
HERETO IRREVOCABLY WAIVE ANY RIGHT TO A JURY TRIAL WITH RESPECT TO ANY ACTION OR
PROCEEDING ARISING OUT OF OR RELATING TO THIS AGREEMENT.

                         17. AMENDMENTS;  WAIVERS. Any provision of this Warrant
may be amended or waived if, and only if, such amendment or waiver is in writing
and signed,  in the case of an amendment,  by the Holder and the Company,  or in
the case of a waiver,  by the party  against whom the waiver is to be effective.
No failure or delay by either party in exercising any right,  power or privilege
hereunder  operate as a waiver  thereof or shall any single or partial  exercise
thereof  preclude any other or further  exercise  thereof or the exercise of any
other right,  power of privilege.  The rights and remedies herein provided shall
be cumulative and not exclusive of any rights or remedies provided by law.

                         18.  COUNTERPARTS.  This Warrant may be executed in any
number of counterparts,  each of which shall be deemed to be an original and all
of which together shall constitute one and the same instrument.

                         19. FCC COMPLIANCE.  Notwithstanding  any provisions of
this  Warrant to the  contrary,  in the event that the consent of the FCC to the
exercise of this Warrant is required to be obtained prior to such exercise, this
Warrant  shall not be  exercisable  unless and until such FCC consent shall have
been  obtained.  In the event that this Warrant is intended to be exercised  and
such FCC consent is required to be  obtained,  the Company and the Holder  shall
use commercially reasonable efforts to obtain such FCC consent promptly.

                            (signature page follows)













                                      - 3 -




             IN WITNESS WHEREOF,  the Company has duly caused this Warrant to be
signed by its duly authorized officer and to be dated as of ________ __, 1998.

                                         AMERICAN MOBILE SATELLITE
                                          CORPORATION



                                         By:____________________________
                                         Name:
                                         Title:

Acknowledged and Agreed:

MOTOROLA, INC.



By:__________________________
Name:
Title:












                                      - 4 -



                                      WARRANT EXERCISE NOTICE

                         (To be delivered prior to exercise of the Warrant
                      by execution of the Warrant Exercise Subscription Form)


To:          American Mobile Satellite Corporation
             10802 Parkridge Blvd.
             Reston, VA  22091

               The undersigned  hereby notifies you of its intention to exercise
the Warrant to purchase  shares of Common  Stock,  par value $.01 per share,  of
American Mobile Satellite  Corporation.  The undersigned intends to exercise the
Warrant to purchase ______________ shares (the "Shares") at $0.01 per Share (the
"Exercise  Price")  [pursuant to the [net  exercise]  [delivery of Common Stock]
 ---------------
provision of Section 2.B of the Warrant].  [The  undersigned  intends to pay the
aggregate  Exercise  Price for the Share in cash,  certified or official bank or
bank cashier's  check or by wire transfer of immediately  available  funds to an
account to designated by the Company or by cancellation of indebtedness  owed to
the Holder (or a combination of such methods) as indicated below.]

             The undersigned  hereby certifies that to the best of its knowledge
its Alien Ownership Percentage as of the date hereof is ___________.

Date: ________________________

                                         -----------------------------
                                         (Signature of Owner)

                                         ------------------------------
                                         (Street Address)

                                         ------------------------------
                                         (City)    (State)   (Zip Code)

Payment:    $_____________ cash
            $_____________ check
            $_____________ wire transfer
            $_____________ cancellation of indebtedness

[Wire  Transfer  Instructions,  if  required  pursuant  to Section 3 or 4 of the
Warrant: _______________________]





                                








                                      - 5 -



                       WARRANT EXERCISE SUBSCRIPTION FORM

                (To be executed only upon exercise of the Warrant
                   after delivery of Warrant Exercise Notice)


To:          American Mobile Satellite Corporation
             10802 Parkridge Blvd.
             Reston, VA  22091

             The undersigned  irrevocably exercises the Warrant for the purchase
of _______________________ shares (the "Shares") of Common Stock, par value $.01
per share, of American Mobile Satellite Corporation (the "Company") at $____ per
Share (the "Exercise Price") and [herewith makes payment of $____________,  such
payment  being made in cash or by certified or official  bank or bank  cashier's
check payable to the order of the Company or by wire transfer or by cancellation
of  indebtedness  owed to the Holder or any  combination  of such  methods] [the
undersigned  Holder is  exercising  the Warrant  pursuant to the [net  exercise]
[delivery of shares of Common  Stock]  provision of Section 2.B of the Warrant],
all on the  terms and  conditions  specified  in the  Warrant,  surrenders  this
Warrant  and all right,  title and  interest  therein to the Company and directs
that the Shares  deliverable  upon the exercise of this Warrant be registered or
placed in the name and at the address specified below and delivered thereto.  If
said  number of Shares is less than all of the shares of Common  Stock for which
the  Warrant  is  exercisable,  the  undersigned  requests  that  a new  Warrant
representing  the remaining  balance of such shares be registered in the name of
the  undersigned  or  nominee  hereinafter  set  forth,  and  further  that such
certificate be delivered to the undersigned at the address hereinafter set forth
or to such other person or entity as is hereinafter set forth.

Date:__________________________


                                         -----------------------------
                                         (Signature of Owner)

                                         ------------------------------
                                         (Street Address)

                                         ------------------------------
                                         (City)    (State)   (Zip Code)




                                








                                      - 6 -



Securities and/or check to be issued to:

Please insert social security or identifying
number:_______________________________________________

Name:  _______________________________________________

Street Address:  _____________________________________

City, State and Zip Code:  ___________________________


Any unexercised  portion of the Warrant  evidenced by the [within] Warrant to be
issued to:

Please insert social security or identifying 
number:_______________________________________________


Name:  _______________________________________________

Street Address:  _____________________________________

City, State and Zip Code:  ___________________________














                                      - 7 -


                             WARRANT ASSIGNMENT FORM

                                                              Dated:____________


          FOR  VALUE  RECEIVED,   _____________________________   hereby  sells,
assigns and transfers unto  ____________________________________________________
(the "Assignee") (please type or print in block letters),

                           (insert Assignee's address)

            --------------------------------------------------------
           (insert Assignee's social security and taxpayer ID number)

its right to  purchase  up to ____ shares of Common  Stock  represented  by this
Warrant  and  does  hereby  irrevocably   constitute  and  appoint  ____________
Attorney,  to transfer the same on the books of the Company,  with full power of
substitution in the premises.



                                                  ----------------------------
                                                  Signature


Signature Guarantee: