RECAPITALIZATION AGREEMENT

          This RECAPITALIZATION AGREEMENT (the "AGREEMENT"), entered into as 
of September 27, 1996, by and between HIGHWAYMASTER COMMUNICATIONS, INC., a 
Delaware corporation (the "COMPANY"), and each of the entities and persons 
listed on EXHIBIT A attached to this Agreement as Carlyle stockholders (the 
"CARLYLE STOCKHOLDERS") and each of the entities and persons listed on 
Exhibit A attached to this Agreement  as Erin Mills Stockholders (the "ERIN 
MILLS STOCKHOLDERS").

                                 BACKGROUND

          Certain of the Carlyle Stockholders beneficially own approximately 
10.3% of the issued and outstanding shares of common stock, par value $.01 
per share (the "COMMON STOCK"), of the Company.

          Certain of the Erin Mills Stockholders beneficially own 
approximately 37.6% of the issued and outstanding shares of Common Stock.

          The Erin Mills Investment Corporation ("EMIC") is the holder of 
promissory notes dated August 23, 1996 and September 16, 1996 in the 
aggregate original principal amount of $5,000,000 (the "BRIDGE NOTES") issued 
pursuant to a Note Purchase Agreement dated August 23, 1996 between the 
Company and EMIC (the "BRIDGE NOTE AGREEMENT").

          The Erin Mills Development Corporation is the holder of 459.6 
shares of Series B Preferred Stock, par value $.01 per share (the "SERIES B 
PREFERRED STOCK"), of the Company.  The Erin Mills Investment Corporation 
("EMIC") is the holder of 120.0 shares of Series B Preferred Stock.  Erin 
Mills International Investment Corporation ("EMIIC") is the holder of 349.505 
shares of Series B Preferred Stock.  Robert S. Folsom is the holder of 42.85 
shares of Series B Preferred Stock.  Robert T. Hayes is the holder of 
108.0450 shares of Series B Preferred Stock.   The holders of shares of 
Series B Preferred Stock are collectively referred to as the "SERIES B 
PREFERRED STOCKHOLDERS."

          Clipper Capital Associates, L.P. is the holder of promissory notes 
dated June 28, 1995 in the original aggregate principal amount of $29,871.76 
(together, "CARLYLE NOTE NO. 1") issued by the Company pursuant to the Note 
Exchange and Amendments Agreement dated May 26, 1995 (the "NOTE EXCHANGE 
AGREEMENT").  Clipper/Merban, L.P. 

                                     -1-



is the holder of promissory notes dated June 28, 1995 in the original 
aggregate principal amount of $1,684,009.32 (together, "CARLYLE NOTE NO. 2") 
issued by the Company  pursuant to the Note Exchange Agreement.  
Clipper/Merchant Partners, L.P. is the holder of promissory notes dated June 
28, 1995 in the original aggregate principal amount of $1,662,712.05 
(together, "CARLYLE NOTE NO. 3") issued by the Company pursuant to the Note 
Exchange Agreement. Carlyle-HighwayMaster Investors, L.P. is the holder of 
promissory notes dated June 28, 1995 in the original aggregate principal 
amount of $5,187,536.53 (together, "CARLYLE NOTE NO. 4") issued by the 
Company pursuant to the Note Exchange Agreement. Carlyle-HighwayMaster 
Investors II, L.P. is the holder of promissory notes dated June 28, 1995 in 
the original aggregate principal amount of $488,604.30 (together, "CARLYLE 
NOTE NO. 5") issued by the Company pursuant to the Note Exchange Agreement. 
Chase Manhattan Investment Holdings, Inc. is the holder of promissory notes 
dated June 28, 1995 in the original aggregate principal amount of 
$1,241,756.43 (together, "CARLYLE NOTE NO. 6") issued by the Company pursuant 
to the Note Exchange Agreement. H.M. Rana Investments Limited is the holder 
of promissory notes dated June 28, 1995 in the original aggregate principal 
amount of $2,110,316 (together, "CARLYLE NOTE NO. 7") issued by the Company 
pursuant to the Note Exchange Agreement.  Archery Partners is the holder of 
promissory notes dated June 28, 1995 in the original aggregate principal 
amount of $215,218.08 (together, "CARLYLE NOTE NO. 8") issued by the Company 
pursuant to the Note Exchange Agreement.  The Carlyle Note No. 1, Carlyle 
Note No. 2, Carlyle Note No. 3, Carlyle Note No. 4, Carlyle Note No. 5, 
Carlyle Note No. 6, Carlyle Note No. 7 and Carlyle Note No. 8 are 
collectively referred to as the "CARLYLE NOTES."  The holders of the Carlyle 
Notes are hereinafter collectively referred to as the "CARLYLE NOTEHOLDERS."

          Concurrently with the execution and delivery of this Agreement, the 
Company is entering into certain transactions (the "INVESTMENT TRANSACTIONS") 
with Southwestern Bell Wireless Holdings, Inc. (the "INVESTOR"). The 
Investment Transactions include, but are not limited to, (i) the issuance and 
sale by the Company of 1,000 shares of its Series D Participating Convertible 
Preferred Stock, par value $.01 per share, to the Investor pursuant to a 
Purchase Agreement (the "PURCHASE AGREEMENT") in exchange for a payment in 
the amount of $20,000,000, (ii) the execution and delivery of an Amended and 
Restated Stockholders' Agreement (the "STOCKHOLDERS' AGREEMENT") among the 
Company, the Carlyle Stockholders, the Erin Mills Stockholders, the Investor 
and certain other stockholders of the Company, (iii) the agreement on the 
part of the Investor to provide certain services to the Company pursuant to a 
Technical Services Agreement (the "TECHNICAL SERVICES AGREEMENT") and (iv) 
the issuance by the Company to the Investor of 5,000,000 warrants to purchase 
shares of Common Stock evidenced by a Warrant Certificate (the "WARRANT 
CERTIFICATE").  The Purchase Agreement, the Stockholders' 

                                     -2-



Agreement, the Technical Services Agreement, and the Warrant Certificate are 
collectively referred to as the "INVESTMENT DOCUMENTS."   Copies of the 
Investment Documents have been provided by the Company to each of the other 
parties to this Agreement.

          In order, among other things, to induce the Investor to enter into 
the Investment Transactions, (i) Erin Mills International Investment 
Corporation ("EMIIC") and The Erin Mills Development Corporation ("EMD") are 
willing to invest $8,000,000 and $2,000,000, respectively, in cash in Common 
Stock; (ii) the Series B Preferred Stockholders are willing to exchange the 
shares of Series B Preferred Stock owned by them for shares of Common Stock 
on the basis described in this Agreement; and (iii) the Carlyle Noteholders 
are willing to exchange the Carlyle Notes for shares of Common Stock on the 
basis described in this Agreement, in each case upon the terms and conditions 
set forth in this Agreement. 

          NOW, THEREFORE, in consideration of the foregoing and the 
respective representations, warranties, covenants, and agreements set forth 
in this Agreement and other good and valuable consideration, the receipt and 
sufficiency of which are hereby acknowledged, the parties to this Agreement 
agree as follows:

          SECTION 1.     RECAPITALIZATION.

          (a)  Concurrently with the execution and delivery of this 
Agreement, the Company will repay in full the principal amount of, and all 
interest accrued on, the Bridge Notes and EMIC will surrender the Bridge 
Notes to the Company for cancellation.

          (b)   Concurrently with the execution and delivery of this 
Agreement, the Company will issue, sell, and deliver (against payment of the 
A Purchase Price (as defined below)) to EMIIC and EMD, and EMIIC and EMD will 
purchase, accept, and receive from the Company, 640,000 and 160,000 shares, 
respectively, of Common Stock, free and clear of all liens, claims and 
encumbrances.  The purchase price (the "A PURCHASE PRICE") for such shares of 
Common Stock to be paid by EMIIC and EMD will be $8,000,000 and $2,000,000, 
respectively, which will be paid to the Company in immediately available 
funds on the date of this Agreement.

          (c)  Concurrently with the execution and delivery of this 
Agreement, the Company will issue, sell and deliver (against payment of the B 
Purchase Price (as defined below)) to the several Erin Mills Stockholders set 
forth on EXHIBIT B attached to this Agreement, and such Erin Mills 
Stockholders severally will purchase, accept and receive from the Company, 
the number of shares of Common Stock set forth opposite their names 

                                     -3-



on such exhibit (the "B STOCK"), free and clear of all liens, claims and 
encumbrances.  The purchase price (the "B PURCHASE PRICE") for the B Stock 
will be paid by the several Erin Mills Stockholders on the date of this 
Agreement by surrender to the Company of the number of shares of Series B 
Preferred Stock set forth on EXHIBIT B attached to this Agreement, duly 
endorsed in blank or accompanied by duly executed blank stock powers, which 
shares will be free and clear of all liens, claims, and encumbrances.

          (d)  Concurrently with the execution and delivery of this 
Agreement, the Company will issue, sell, and deliver (against payment of the 
C Purchase Price (as defined below)) to the Carlyle Noteholders, and the 
Carlyle Noteholders severally will purchase, accept and receive from the 
Company, the number of shares of Common Stock determined by dividing (i) the 
sum of the principal amount of the Carlyle Notes held by each Carlyle 
Noteholder as set forth in the recitals to this Agreement and the amount of 
interest accrued and unpaid on each Carlyle Note set forth on EXHIBIT C 
hereto (the "EXCLUDED INTEREST") by (ii) $12.50 (the "C SHARES"), free and 
clear of all liens, claims, and encumbrances.  The purchase price (the "C 
PURCHASE PRICE") for the C Shares will be paid by the several Carlyle 
Stockholders on the date of this Agreement by surrender to the Company of 
each of the Carlyle Notes for cancellation, which notes will be free and 
clear of all liens, claims, and encumbrances.  No fractional shares or scrip 
representing fractional shares will be issued upon the exchange of the 
Carlyle Notes for the C Shares in accordance with this SECTION 1(d).  If any 
such exchange would require the issuance of a fractional share, an amount 
equal to such fraction multiplied by the Closing Price (as defined below) of 
the Common Stock on the trading day immediately preceding the date of this 
Agreement will be paid to the holder in cash by the Company.  In addition, 
concurrently with the execution and delivery of this Agreement, the Company 
will pay to the Carlyle Noteholders in cash on the date hereof all accrued 
and unpaid interest on the Carlyle Notes, other than the Excluded Interest.  
As used herein, the term "Closing Price" shall mean on any day the reported 
last sale price per share of Common Stock regular way on such day or, in case 
no such sale takes place on such day, the average of the reported closing bid 
and asked prices regular way, in each case on the New York Stock Exchange, 
or, if the shares of Common Stock are not listed or admitted to trading on 
such Exchange, the principal national securities exchange on which the shares 
of Common Stock are listed or admitted to trading, or, if the Common Stock is 
not listed or admitted to trading on any national securities exchange, the 
last quoted sale price or, if not so quoted, the average of the closing bid 
and asked prices quoted on the Nasdaq National Market, or, if not so quoted, 
the average of the closing bid and asked prices as furnished by any member of 
the National Association of Securities Dealers, Inc. selected from time to 
time by the corporation for that purpose.

                                     -4-



          (e)  The closing of the transactions provided for in this SECTION 1 
(the "CLOSING") will take place at the offices of the Company (or at such 
other place as is specified by the Company) on the date of this Agreement. 

          SECTION 2.     TERMINATED DOCUMENTS.  Effective upon the execution 
and delivery of this Agreement and without any other action, each of the 
Carlyle Stockholders and the Erin Mills Stockholders, severally and not 
jointly, hereby (a) agrees that the Terminated Documents (as defined below) 
will terminate and be of no further force and effect and that it will have no 
further rights thereunder; and (b) represents and warrants with respect to 
itself that it has not transferred any of its rights or interests under or in 
respect of the Terminated Documents and that such party has the sole right, 
capacity, and exclusive authority to terminate its rights under the 
Terminated Documents.  As used in this Agreement, the term "TERMINATED 
DOCUMENTS" means (i) the Subscription Agreement dated as of February 4, 1994 
by and among the Company (formerly known as HM Holding Corporation) and the 
other parties named in such agreement, as amended to the date of this 
Agreement; (ii) the Bridge Note and the Bridge Note Agreement; and (iii) the 
Carlyle Notes.

          SECTION 3.     INVESTMENT INTENT.  Each of the Carlyle Stockholders 
and the Erin Mills Stockholders hereby severally and not jointly represents 
and warrants to the Company that the shares of Common Stock to be acquired by 
such party pursuant to this Agreement are to be acquired for the such party's 
own account for investment and not with a view to, or for resale in 
connection with, any distribution of such shares within the meaning of the 
Securities Act of 1933, as amended (the "SECURITIES ACT").

          SECTION 4.     INVESTOR STATUS.  In connection with the purchase of 
the shares of Common Stock, each of the Erin Mills Stockholders and the 
Carlyle Stockholders hereby severally and not jointly represents and warrants 
to the Company with respect to itself as follows:

          (a)  Such party acknowledges that the shares of Common Stock are 
not registered under the Securities Act or any applicable state securities 
law, and that such shares may not be transferred or sold except pursuant to 
the registration provisions of the Securities Act or pursuant to an 
applicable exemption therefrom and pursuant to such state securities laws and 
regulations as may be applicable.

          (b)  Such party is knowledgeable, sophisticated, and experienced in 
business and financial matters of the type contemplated by this Agreement and 
is able to bear the economic risks associated with its investment in the 
Company. Such party has 

                                     -5-



been afforded access to information regarding the Company and its 
subsidiaries and their respective financial condition, operating results, 
properties, liabilities, operations, and management sufficient to enable it 
to evaluate the risks and merits of its investment in the Company.

          SECTION 5.     OTHER REPRESENTATIONS OF THE ERIN MILLS 
STOCKHOLDERS. Each of the Erin Mills Stockholders hereby further severally 
and not jointly represents and warrants to the Company with respect to itself 
as follows:

          (a)  The execution, delivery and performance of this Agreement and 
the consummation of the transactions contemplated by this Agreement have been 
duly authorized by such Erin Mills Stockholder.  This Agreement has been duly 
executed by such Erin Mills Stockholder and constitutes a valid and binding 
obligation of such Erin Mills Stockholder, enforceable in accordance with its 
terms.

          (b)  The execution, delivery, and performance by such Erin Mills 
Stockholder of this Agreement and the consummation of the transactions 
contemplated by this Agreement: (i) is within such Erin Mills Stockholder's 
corporate or partnership power and authority and has been duly authorized by 
all necessary corporate or partnership action on the part of such Erin Mill 
Stockholder, as appropriate; (ii) does not and will not conflict with or 
contravene the terms of or require any consent, authorization, or approval 
pursuant to such Erin Mills Stockholder's certificate of incorporation or 
bylaws, partnership agreement or similar organizational document; (iii) does 
not and will not violate, conflict with, or result in any breach or 
contravention of or require any consent, authorization, approval, exemption, 
or other action by or notice or declaration to, or filing with, any court or 
administrative or governmental body or agency or other person pursuant to (A) 
any material agreement, lease, or contract of such Erin Mills Stockholder, or 
(B) any applicable statute or any rule or regulation of any governmental 
authority or any order or decree applicable to such Erin Mills Stockholder.

          SECTION 6.     OTHER REPRESENTATIONS OF THE CARLYLE STOCKHOLDERS. 
Each of the Carlyle Stockholders hereby further severally and not jointly 
represents and warrants to the Company with respect to itself as follows:

          (a)  The execution, delivery and performance of this Agreement and 
the consummation of the transactions contemplated by this Agreement have been 
duly authorized by such Carlyle Stockholder.  This Agreement has been duly 
executed by such Carlyle Stockholder and constitutes a valid and binding 
obligation of such Carlyle Stockholder, enforceable in accordance with its 
terms.

                                     -6-



          (b)  The execution, delivery, and performance by such Carlyle 
Stockholder of this Agreement and the consummation of the transactions 
contemplated by this Agreement: (i) is within such Carlyle Stockholder's 
corporate or partnership power and authority and has been duly authorized by 
all necessary corporate or partnership action on the part of such Carlyle 
Stockholder, as appropriate; (ii) does not and will not conflict with or 
contravene the terms of or require any consent, authorization, or approval 
pursuant to such Carlyle Stockholder's certificate of incorporation or 
bylaws, partnership agreement or similar organizational document; (iii) does 
not and will not violate, conflict with, or result in any breach or 
contravention of or require any consent, authorization, approval, exemption, 
or other action by or notice or declaration to, or filing with, any court or 
administrative or governmental body or agency or other person pursuant to (A) 
any material agreement, lease, or contract of such Carlyle Stockholder, or 
(B) any applicable statute or any rule or regulation of any governmental 
authority or any order or decree applicable to such Carlyle Stockholder.

          SECTION 7.     REPRESENTATIONS OF THE COMPANY.  The Company hereby 
represents and warrants to each of the Carlyle Stockholders and the Erin 
Mills Stockholders as follows:

          (a)  The execution, delivery, and performance of this Agreement and 
the consummation of the transactions contemplated by this Agreement have been 
duly authorized by the Company.  This Agreement has been duly executed by the 
Company and constitutes a valid and binding obligation of the Company, 
enforceable in accordance with its terms.  All outstanding shares of the 
Company's capital stock are, and the shares of Common Stock to be issued to 
the several Carlyle Stockholders and Erin Mills Stockholders will be upon 
such issuance and receipt by the Company of payment therefor, duly 
authorized, fully paid, and nonassessable.  The offer, sale, and issuance of 
the Common Stock to the several Carlyle Stockholders and the Erin Mills 
Stockholders under this Agreement do not require registration under the 
Securities Act or any applicable state securities laws or blue sky laws, 
assuming that all representations made by the Carlyle Stockholders and the 
Erin Mills Stockholders in SECTIONS 3 and 4 are true.

          (b)  Each of the representations made by the Company in Section 3 
of the Purchase Agreement is true and correct and is incorporated by this 
reference into this Agreement, except that (i) the Company makes no 
representation to the Erin Mills Stockholders or the Carlyle Stockholders as 
to the matters set forth in the first two sentences of Section 3(b)(iii) or 
in Section 3(b)(iv) of the Purchase Agreement; and (ii) each reference to 
"prejudice in any material respect the rights of the Investor under any of 
the Transaction Documents" will be deemed to read as "prejudice in any 
material respect 

                                     -7-



the rights of the Carlyle Stockholders or the Erin Mills Stockholders under 
this Agreement."

          SECTION 8.     SURVIVAL AND INDEMNIFICATION.

          (a)  SURVIVAL OF REPRESENTATIONS, WARRANTIES, COVENANTS, AND 
AGREEMENTS; KNOWLEDGE OF BREACH.  Notwithstanding any otherwise applicable 
statute of limitation, the representations and warranties of the Company 
included or provided for in this Agreement will survive the execution and 
delivery of this Agreement until the expiration of nine months after the 
receipt by the Erin Mills Stockholders and the Carlyle Stockholders of 
audited consolidated financial statements for the Company, as of and for the 
year ending December 31, 1996, together with a report thereon by the 
Company's independent public accountants; PROVIDED, HOWEVER, that any 
representation, warranty, covenant, or agreement contained in Sections 3(j) 
and 3(n) of the Purchase Agreement and incorporated by reference in this 
Agreement will survive the execution and delivery of this Agreement until the 
expiration of the applicable statute of limitations (including any waivers or 
extensions thereof) with respect to such matters; PROVIDED, FURTHER, that the 
provisions of this SECTION 8 will constitute the exclusive remedy on the part 
of the Erin Mills Stockholders and the Carlyle Stockholders in respect of a 
breach of the representations and warranties of the Company contained in this 
Agreement.  The covenants and other agreements contained in this Agreement 
will survive the execution and delivery of this Agreement until the date or 
dates specified in such covenant or agreement or the expiration of the 
applicable statute of limitations (including any waivers or extensions 
thereof) with respect to such matters, whichever is later.  In no event will 
the Company be liable (i) to the Carlyle Stockholders for any breach of the 
representations, warranties, covenants, and agreements included or provided 
for in this Agreement or other document delivered pursuant to this Agreement, 
unless and until all claims for which aggregate damages are recoverable under 
this Agreement by the Carlyle Stockholders  exceed the product of (x) 
$250,000 and (y) a fraction the numerator of which is the total numbers of 
shares of Common Stock issued to the Carlyle Stockholders pursuant to this 
Agreement and the denominator is the total number of shares issued by the 
Company pursuant to this Agreement (the "CARLYLE STOCKHOLDER DEDUCTIBLE") or 
(ii) to the Erin Mills  Stockholders for any breach of the representations, 
warranties, covenants, and agreements included or provided for in this 
Agreement or other document delivered pursuant to this Agreement, unless and 
until all claims for which aggregate damages are recoverable under this 
Agreement by the Erin Mills Stockholders  exceed the product of (x) $250,000 
and (y) a fraction the numerator of which is the total numbers of shares of 
Common Stock issued to the Erin Mills Stockholders pursuant to this Agreement 
and the denominator is the total number of shares issued by the Company 
pursuant to this Agreement (the "ERIN MILLS  

                                     -8-



STOCKHOLDER DEDUCTIBLE"), in which case such party will be entitled to 
damages equal to such excess, but, in the case of the Carlyle Stockholders 
and the Erin Mills Stockholders, not more than the purchase price paid by 
such party for the Common Stock acquired under this Agreement by such party 
plus the charges and expenses (including reasonable attorneys' fees and 
expenses) incurred by such party sustaining such damages in connection with 
this Agreement and the transactions contemplated hereby;

          (b)  INDEMNIFICATION. For a period commencing on the date of this 
Agreement and ending, as the case may be, upon the expiration of the periods 
specified in SECTION 8(a), the Company, on the one hand, and each Erin Mills 
Stockholder or Carlyle Stockholder, as applicable, on the other, (the 
"INDEMNIFYING PARTY"), will, subject to the limitations set forth in SECTION 
8(a), indemnify the Erin Mills Stockholders or the Carlyle Stockholders, on 
the one hand, or the Company on the other, as the case may be (the 
"INDEMNIFIED PARTY"), against and in respect of all losses, damages, 
liabilities, costs, and expenses (including reasonable attorneys' fees and 
expenses) incurred in investigating, preparing or defending any claims 
covered by this SECTION 8(b) sustained or incurred arising out of any 
breaches by such Indemnifying Party of its representations, warranties, 
covenants, and agreements set forth in this Agreement (it being understood 
and agreed that no Carlyle Stockholder or Erin Mills Stockholder shall be 
obligated to indemnify the Company pursuant to this SECTION 8(b) as a result 
of a breach of any representation, warranty, covenant, or agreement on the 
part of any other party hereto). The indemnification provided for by this 
SECTION 8(b) will apply notwithstanding any investigation made by or on 
behalf of any party.  Any payments pursuant to this SECTION 8(b) will be 
treated as an adjustment to the purchase price for all tax purposes.

          (c)  METHOD OF ASSERTING CLAIMS. In the event that an Indemnified 
Party shall assert a claim for indemnity under this SECTION 8, (i) the 
Indemnified Party will promptly after the receipt of notice of the 
commencement of any action, investigation, claim, demand or other proceeding 
by a third party against such Indemnified Party in respect of which indemnity 
may be sought from any Indemnifying Party under this Section 8, notify the 
Indemnifying Party in writing of the commencement thereof or (ii) if the 
claim is other than such a third party claim, the Indemnified Party will 
notify the Indemnifying Party promptly following its discovery of the facts 
or circumstances giving rise thereto; PROVIDED, that in either case (i) or 
(ii), no such notice need be provided by the Company to an Indemnifying Party 
who is a Carlyle Stockholder or an Erin Mills Stockholder if the Carlyle 
Stockholder Deductible or Erin Mills Stockholder Deductible, as applicable, 
has not been exceeded and will not be exceeded by such claim or demand and 
the omission of the Indemnified Party to so notify such Indemnifying Party of 
any such action will not relieve such Indemnifying Party from any liability 
that it may have to such Indemnified 

                                     -9-



Party under this SECTION 8(c) unless, and only to the extent that, such 
omission prejudices the ability of the Indemnifying Party to defend such 
action, investigation, claim, demand, or other proceeding or to reduce or 
mitigate its liability under this SECTION 8, whether as a result of the 
forfeiture of substantive rights or defenses or otherwise.  In case any such 
action, claim, or other proceeding is brought against the Indemnified Party 
such Indemnified Party will notify the applicable Indemnifying Party of the 
commencement thereof, the Indemnifying Party will be entitled to assume the 
defense thereof at its own expense, with counsel satisfactory to such 
Indemnified Party in its reasonable judgment, PROVIDED that the Deductible 
has been or will be exceeded; PROVIDED, FURTHER, that the Indemnified Party 
may, at its own expense, retain separate counsel to participate in such 
defense. Notwithstanding the foregoing, in any action, claim or proceeding in 
which both the Indemnifying Party, on the one hand, and an Indemnified Party, 
on the other hand, is, or is reasonably likely to become, a party, such 
Indemnified Party shall have the right to employ separate counsel at the 
Indemnifying Party's expense and to control its own defense of such action, 
claim or proceeding if, in the reasonable opinion of counsel to such 
Indemnified Party, a conflict or potential conflict exists between the 
Indemnifying Party, on the one hand, and such Indemnified Party, on the other 
hand, that would prevent the representation of the Indemnified Party by 
counsel selected by and subject to the control of the Indemnifying Party 
under applicable law or codes of professional responsibility.  Each of the 
Company, the Erin Mills Stockholders, and the Carlyle Stockholders agrees 
that it will not, without the prior written consent of the Indemnified Party, 
settle, compromise, or consent to the entry of any judgment in any pending or 
threatened claim, action, or proceeding relating to the matters contemplated 
by this SECTION 8 (if the Indemnified Party is a party thereto or has been 
actually threatened to be made a party thereto) unless such settlement, 
compromise, or consent includes an unconditional release of the Indemnified 
Party from all liability arising or that may arise out of such claim, action 
or proceeding.

          SECTION 9. COVENANTS.

          (a)  INSPECTION RIGHTS. The Company will permit, and cause its 
subsidiaries to permit, the representatives designated by the Erin Mills 
Stockholders and the Carlyle Stockholders so long as (i) the Erin Mills 
Stockholders and the Carlyle Stockholders and their affiliates together 
beneficially own 1,600,000 shares of Common Stock or (ii) the representation 
and warranties of the Company set forth in this Agreement survive, upon 
reasonable notice and during normal business hours, to (x) visit and inspect 
any of the properties of the Company and its subsidiaries, (y) examine the 
corporate and financial records of the Company and its subsidiaries and to 
make copies thereof, and (z) discuss the affairs, finances and accounts of 
any such entities with the directors, officers, 

                                     -10-



key employees, and (with the prior consent of the Company, which will not be 
unreasonably withheld) independent accountants of the Company and its 
subsidiaries.

          (b)  CONFIDENTIALITY.    Each of the Erin Mills Stockholders and 
the Carlyle Stockholders will hold in confidence all information and data 
obtained by it from the Company or its subsidiaries (whether in connection 
with the negotiation of the transactions contemplated by this Agreement, 
pursuant to SECTION 9(a) or otherwise) and will not disclose such information 
to any person or entity without the prior written consent of the Company 
(except that the Erin Mills Stockholders and the Carlyle Stockholders may 
disclose such information to their affiliates, directors, officers, and other 
representatives who require access to such information in order to enable 
them to exercise their rights under this Agreement or for any other proper 
purpose contemplated thereby and who agree to be subject to the restrictions 
set forth in this SECTION 9(b)); PROVIDED, HOWEVER, that the provisions of 
this SECTION 9(b) will not apply to any information or data that can be shown 
(i) to be generally available to the public through no fault of such party or 
its affiliates, directors, officers, and other representatives or (ii) to 
have been lawfully obtained by the Erin Mills Stockholders or the Carlyle 
Stockholders from other sources not subject to a confidentiality obligation 
to the Company.

          SECTION 10. APPLICABLE LAW.  THIS AGREEMENT WILL BE GOVERNED BY AND 
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF DELAWARE, WITHOUT 
REGARD TO ANY CONFLICTS OF LAW PRINCIPLES THAT WOULD REQUIRE THE APPLICATION 
OF THE LAWS OF ANY OTHER JURISDICTION.

          SECTION 11.    PARTIES IN INTEREST; ASSIGNMENT.  This Agreement 
will be binding on and will inure to the benefit of the parties to this 
Agreement and their respective successors and permitted assigns.  No party 
may assign this Agreement or its rights and benefits under this Agreement or 
delegate and duties under this Agreement to any other person or entity 
without the prior written consent of the other parties.

          SECTION 12.    AMENDMENT; WAIVER.  The provisions of this Agreement 
may be amended only by a written instrument executed by each of parties to 
this Agreement, and compliance with the provisions of this Agreement may be 
waived only by a written instrument executed by each party entitled to the 
benefits of such provision.  No failure on the part of any party to exercise 
any right, power, or privilege granted under this Agreement will operate as a 
waiver of such right, power, or privilege, nor will any single or partial 
exercise of such right, power, or privilege preclude any other or further 
exercise of such right, power, or privilege or the exercise of any other 
right, power or privilege granted under this Agreement.

                                     -11-



          SECTION 13.    FURTHER ASSURANCES.  Each party agrees to do, or 
cause to be done, such further acts and to execute and deliver, or to cause 
to be executed and delivered, such further agreements, instruments, 
certificates, and other documents as may be necessary or appropriate to 
effectuate and carry out the purposes of this Agreement.

          SECTION 14.    NOTICES AND OTHER COMMUNICATIONS.  All notices and 
other communications under this Agreement will be in writing and will be 
given by delivery in person, by registered or certified mail (return receipt 
requested and with postage prepaid thereon) or by cable, telex or facsimile 
transmission to the parties at the following addresses (or at such other 
address as either party will have furnished to the other in accordance with 
the terms of this SECTION 14):

if to the Company, to:

HighwayMaster Communications, Inc.
16479 Dallas Parkway
Suite 710
Dallas, Texas 75248
Attention: William C. Kennedy, Jr.

if to any of the Erin Mills Stockholders, to:

Erin Mills International Investment Corporation
Trident House, Suite 204(a)
Broad Street
Bridgetown, Barbados
West Indies
Attention: Stephen Greaves

if to any of the Carlyle Stockholders (except for the Carlyle Stockholders 
that are Clipper Stockholders (as defined in the Stockholders' Agreement)), 
to:

The Carlyle Group, L.P.
1001 Pennsylvania Avenue
Suite 220 South
Washington, D.C. 20004-2505
Attention: Mark D. Ein

                                     -12-



if to any Clipper Stockholders, to:

The Clipper Group, L.P.
12 East 49th Street
New York, New York 10017
Attention: Daniel V. Cahillane

All notices and other communications under this Agreement that are addressed 
as provided in or pursuant to this SECTION 14 will be deemed duly and validly 
given (a) if delivered in person, upon delivery, (b) if delivered by 
registered or certified mail (return receipt requested and with postage paid 
thereon), 72 hours after being placed in a depository of the United States 
mails; and (c) if delivered by cable, telex, or facsimile transmission, upon 
transmission thereof and receipt of the appropriate answer back.

          SECTION 15.    ENTIRE AGREEMENT.  This Agreement constitutes the 
entire agreement and understanding of the parties to this Agreement with 
respect to the subject matter of this Agreement and supersedes any prior or 
contemporaneous oral and prior written agreements or understandings between 
the parties with respect to the subject matter of this Agreement.  

          SECTION 16.    HEADINGS.  The section headings contained in this 
Agreement are inserted for the convenience of reference only and are not 
intended to be a part of or to affect the meaning or interpretation of this 
Agreement.

          SECTION 17.    COUNTERPARTS.  This Agreement may be executed in one 
or more counterparts, each of which will be deemed an original and all of 
which together will constitute one and the same instrument.

          SECTION 18.    NO GROUP OR BENEFICIAL OWNERSHIP.  Nothing in this 
Agreement will be deemed to constitute any party to this Agreement as member 
of a "group" for the purposes of the Securities Exchange Act of 1934, as 
amended, or to be an admission that any party to this Agreement beneficially 
owns any of the securities of any other party to this Agreement.

          SECTION 19.    EXPENSES. The Company will (i) reimburse each of the 
Carlyle Stockholders and the Erin Mills Stockholders for stamp and other 
stock issuance or similar taxes that may be payable in respect of the 
execution and delivery of this Agreement or the issuance, delivery, or 
acquisition of any shares of Common Stock to be issued under this Agreement 
(but excluding any income or similar state of federal taxes).  

                                     -13-



Except as otherwise expressly provided in this Agreement, the parties will 
bear their own respective expenses (including, but not limited to, all 
compensation and expenses of counsel, financial advisors, consultants, 
actuaries, and independent accountants) incurred in connection with this 
Agreement and the transactions contemplated by this Agreement or the 
Investment Documents.

          SECTION 20.    LIMITATION ON COMPANY REPRESENTATIONS.  
Notwithstanding any provision of this Agreement to the contrary, the Company 
makes no representation or warranty, and will have no obligation to indemnify 
or liability for damages for, any matter to the extent that the material 
facts with respect to such matter are known to any Carlyle Stockholders or 
Erin Mills Stockholders as of the date of this Agreement.

                     [REMAINDER OF PAGE INTENTIONALLY BLANK]

                                     -14-



          IN WITNESS WHEREOF, the parties to this Agreement have caused this 
Agreement to be duly executed as of the date first above written.

                    HIGHWAYMASTER COMMUNICATIONS, INC.


                    By:    /s/ William C. Saunders                  
                           ------------------------------------------
                    Name:  William C. Saunders                       
                           ------------------------------------------
                    Title: President                                 
                           ------------------------------------------

                    CLIPPER CAPITAL ASSOCIATES, L.P.

                    By: CLIPPER CAPITAL ASSOCIATES, INC.
                    Its:  General Partner

                         By:    /s/ Daniel V. Cahillane                
                                -------------------------------------
                         Name:  Daniel V. Cahillane                   
                                -------------------------------------
                         Title: Treasurer & Secretary                   
                                -------------------------------------

                    CLIPPER/MERBAN, L.P.

                    By: CLIPPER CAPITAL ASSOCIATES, L.P.
                    Its:  General Partner

                         By: CLIPPER CAPITAL ASSOCIATES, INC.
                         Its: General Partner


                         By:    /s/ Daniel V. Cahillane              
                                -------------------------------------
                         Name:  Daniel V. Cahillane                   
                                -------------------------------------
                         Title: Treasurer & Secretary                 
                                -------------------------------------

                                     -15-



                    CLIPPER/MERCHANT PARTNERS, L.P.

                    By: CLIPPER CAPITAL ASSOCIATES, L.P.
                    Its:  General Partner

                         By: CLIPPER CAPITAL ASSOCIATES, INC.
                         Its: General Partner

                         By:    /s/ Daniel V. Cahillane                   
                                --------------------------------------------
                         Name:  Daniel V. Cahillane                     
                                --------------------------------------------
                         Title: Treasurer & Secretary                  
                                --------------------------------------------

                    CARLYLE-HIGHWAYMASTER INVESTORS, L.P.

                    By: T.C. GROUP, L.L.C.
                    Its:  General Partner

                         By:    /s/ Mark D. Ein                            
                                ---------------------------------------------
                         Name:  Mark D. Ein                            
                                ---------------------------------------------
                         Title: Vice-President of Managing Member of TC Group
                                ---------------------------------------------

                    CARLYLE-HIGHWAYMASTER INVESTORS II, L.P.

                    By: T.C. GROUP, L.L.C.
                    Its:  General Partner


                         By:    /s/ Mark D. Ein                              
                                ---------------------------------------------
                         Name:  Mark D. Ein                                  
                                ---------------------------------------------
                         Title: Vice-President of Managing Member of TC Group
                                ---------------------------------------------

                    CHASE MANHATTAN INVESTMENT HOLDINGS,                   
                         INC.

                         By:    /s/ Jeffrey C. Walker                       
                                ---------------------------------------------
                         Name:  Jeffrey C. Walker                           
                                ---------------------------------------------
                         Title: Chief Executive Officer                     
                                ---------------------------------------------

                                     -16-



                    H.M. RANA INVESTMENTS LIMITED

                    By:       --------------------------------------

                         By:   /s/ Fahad A. Almubarak                         
                                -------------------------------------
                         Name:      Fahad A. Almubarak                        
                                -------------------------------------
                         Title:     President                                 
                                -------------------------------------

                    ARCHERY PARTNERS

                    By:       --------------------------------------
                    Its:      General Partner

                         By:    /s/ Jeffrey C. Walker                       
                                -------------------------------------
                         Name:  Jeffrey C. Walker                           
                                -------------------------------------
                         Title: Managing Partner                            


                    THE ERIN MILLS INVESTMENT CORPORATION

                    By:    /s/ G. C. Quinn                                   
                           -----------------------------------------
                    Name:  G. C. Quinn                                      
                           -----------------------------------------
                    Title: President                                        
                           -----------------------------------------
                         
     
                    THE ERIN MILLS DEVELOPMENT CORPORATION

                    By:    /s/ G. C. Quinn                                  
                           -----------------------------------------
                    Name:  G. C. Quinn                                      
                           -----------------------------------------
                    Title: Executive Vice-President                         
                           -----------------------------------------


                    ERIN MILLS INTERNATIONAL INVESTMENT 
                         CORPORATION

                    By:    /s/ S. L. Greaves                                  
                           -----------------------------------------
                    Name:  Stephen L. Greaves                               
                           -----------------------------------------
                    Title: General Manager                                  
                           -----------------------------------------

                                     -17-



                    /s/ Robert T. Hayes by Douglas Dunlap Attorney-in-fact  
                    ----------------------------------------------------------
                    Robert T. Hayes



                    /s/ Robert S. Folsom by Haddon O. Winkler Attorney-in fact
                    ----------------------------------------------------------
                    Robert S. Folsom

                                     -18-



                                                                     EXHIBIT A

1.   CARLYLE STOCKHOLDERS.

     Clipper Capital Associates, L.P.
     Clipper/Merban, L.P.
     Clipper/Merchant Partners, L.P.
     Carlyle-HighwayMaster Investors, L.P.
     Carlyle-HighwayMaster Investors II, L.P.
     Chase Manhattan Investment Holdings, Inc.
     H.M. Rana Investments Limited
     Archery Partners

2.   ERIN MILLS STOCKHOLDERS.

     The Erin Mills Investment Corporation
     The Erin Mills Development Corporation
     Erin Mills International Investment Corporation
     Robert T. Hayes
     Robert S. Folsom

                                     -19-



                                                                     EXHIBIT B

       NAME                  NUMBER OF SHARES OF B   NUMBER OF SHARES OF SERIES
                              STOCK TO BE RECEIVED    B PREFERRED STOCK TO BE
                                                            SURRENDERED

The Erin Mills Development         367,680                      459.6
  Corporation

The Erin Mills Investment           96,000                      120.0
  Corporation

Erin Mills International           279,604                      349.505
  Investment Corporation

Robert T. Hayes                     86,436                      108.0450

Robert S. Folsom                    34,280                       42.85
                                   -------                    ----------
      TOTALS                       864,000                    1,080
                                   -------                    ----------
                                   -------                    ---------- 

                                     -20-



                                                                     EXHIBIT C


NAME                                                          EXCLUDED INTEREST

Clipper Capital Associates, L.P.                                  $   148.96
Clipper/Merban, L.P.                                                8,396.97
Clipper/Merchant Partners, L.P.                                     8,290.78
Carlyle-HighwayMaster Investors, L.P.                              25,866.62
Carlyle-HighwayMaster Investors II, L.P.                            2,436.33
Chase Manhattan Investment Holdings, Inc.                           6,191.77
H.M. Rana Investments Limited                                      10,522.67
Archery Partners                                                    1,282.93
                                                                  ----------
                                                                  $63,137.03
                                                                  ----------
                                                                  ----------

                                     -21-