CERTIFICATE OF AMENDMENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                       HIGHWAYMASTER COMMUNICATIONS, INC.


          HighwayMaster Communications, Inc., a corporation organized and 
existing under the General Corporation Law of the State of Delaware,

          DOES HEREBY CERTIFY

          FIRST:  That at a meeting of the Board of Directors of 
HighwayMaster Communications, Inc. (the "corporation"), resolutions were duly 
adopted setting forth proposed amendments of the Certificate of Incorporation 
of the corporation, declaring such amendments to be advisable and directing 
that such amendments be presented to the stockholders of the corporation for 
consideration thereof.  The resolutions setting forth the proposed amendments 
are as follows:

          RESOLVED, that the second sentence of Article XII of the 
corporation's Certificate of Incorporation be deleted and that Article IV of 
the corporation's Certificate of Incorporation be amended in its entirety to 
read as follows:

          The aggregate number of shares of capital stock which the 
corporation shall have authority to issue is 50,021,000, consisting of 
50,000,000 shares of common stock, par value $0.01 per share (the "Common 
Stock"), 1,000 shares of Class B Common Stock, par value $0.01 per share (the 
"Class B Common Stock"), and 20,000 shares of preferred stock, par value 
$0.01 per share (the "Preferred Stock").  The Common Stock and the Class B 
Common Stock are hereinafter collectively referred to as the "Company Common 
Stock".

                            A.  COMPANY COMMON STOCK

          Except as otherwise expressly provided herein, all shares of Company
Common Stock shall be identical and shall entitle the holders thereof to the
same rights and privileges.

                         


          1.   DIVIDENDS

          (a)  Subject to the rights granted to the holders of any Preferred 
Stock that may be outstanding, the holders of Common Stock shall be entitled 
to receive dividends and distributions when and as declared by the Board of 
Directors of the corporation out of funds legally available therefor.

          (b)  Subject to the rights of the holders of any Preferred Stock 
that may be outstanding, the holders of shares of Class B Common Stock shall 
be entitled to receive, when and as declared by the Board of Directors, but 
only out of funds legally available therefor, dividends and distributions, on 
each date that dividends or other distributions (other than dividends or 
distributions payable in Common Stock of the corporation) are payable on or 
in respect of Common Stock, in an amount per share of Class B Common Stock 
equal to the aggregate amount of dividends or other distributions (other than 
dividends or distributions payable in Common Stock of the corporation) that 
would be payable on such date to a holder of the Reference Package (as 
defined below). Each such dividend and distribution shall be paid to the 
holders of record of shares of Class B Common Stock on the date, not 
exceeding sixty days preceding such dividend or distribution payment date, 
fixed for that purpose by the Board of Directors in advance of payment of 
each particular dividend or distribution, which shall be the same record date 
as for the payment of dividends or distributions on the Common Stock.

          (c)  The term "REFERENCE PACKAGE" shall initially mean 1,600 shares 
of Common Stock of the corporation.  In the event the corporation shall at 
any time after the close of business on September  27, 1996 (A) declare or 
pay a dividend on or distribution in respect of any Common Stock payable in 
Common Stock, (B) subdivide any Common Stock, (C) combine any Common Stock 
into a smaller number of shares or (D) change or reclassify the Common Stock 
(whether pursuant to a merger or consolidation or otherwise), then and in 
each such case the Reference Package after such event shall be the Common 
Stock that a holder of the Reference Package immediately prior to such event 
would hold thereafter as a result thereof.  The Board of Directors may make 
such adjustments in the Reference Package, in addition to those required 
hereby, as shall be determined by the Board, as evidenced by a Board 
resolution, to be necessary and advisable in order to avoid taxation so far 
as practicable of any dividend of stock or stock rights or any event treated 
as such for Federal income tax purposes to the recipients.  Whenever any 
adjustment is required in the Reference Package, the corporation shall 
forthwith (i) file at the principal office of the corporation a statement 
describing in reasonable detail the adjustment and the method of calculation 
used, and (ii) cause a copy of such statement to be mailed by first class 
mail postage prepaid to the holders of record of the Class B Common Stock as 
of the 

                                       2



effective date of such adjustment.  The corporation may obtain the 
certificate of any independent firm of public accountants of national 
recognition selected by the Board of Directors which, if obtained, shall be 
presumptive evidence of the correctness of any computation made under Section 
1(c).

          2.   VOTING RIGHTS

          (a)  GENERAL.  The holders of Common Stock and Class B Common Stock 
shall have identical voting rights and vote together as a single class on all 
actions to be taken by such holders, except as specified below.  Each share 
of Common Stock shall, when entitled to vote, have one vote and each share of 
Class B Common Stock shall, when entitled to vote, have the number of votes 
that a holder of the Reference Package would have.

          (b)  ELECTION OF DIRECTORS.  There shall be two classes of 
directors, those elected by the Common Stock ("Common Directors") and those 
elected by the Class B Common Stock ("Class B Directors").  The rights, 
duties and authority of the Common Directors and the Class B Directors shall 
be identical in all respects.  The number of Common Directors shall be the 
number to be determined by the Nominating Committee of the Corporation.  The 
number of Class B Directors shall be one, except that if Southwestern Bell 
Wireless Holdings, Inc. ("SBW") and its Affiliates Beneficially Own (as 
hereinafter defined) 20% or more of the outstanding Common Stock, including 
Common Stock issuable upon conversion of Class B Common Stock or other 
convertible securities or upon the exercise of any outstanding options, 
warrants, rights or obligations, other than shares issuable upon the exercise 
of (i) the 5,000,000 warrants issued on September 27, 1996 (the "Warrants"), 
and (ii) options, warrants, rights or obligations issued by any entity other 
than the corporation ("Excluded Options"), there shall be two Class B 
Directors.  For the purposes of the foregoing calculations, the number of 
outstanding shares of Common Stock shall include all shares issuable upon 
conversion of outstanding convertible securities or upon exercise of 
outstanding options, warrants, rights or obligations other than the Warrants, 
Excluded Options and employee stock options.  As used herein, an "Affiliate" 
of any specified person or entity means any person or entity directly or 
indirectly controlling or controlled by or under direct or indirect common 
control with such person.  As used herein, the term "Beneficially Own" (and 
correlative terms) shall mean, with respect to any shares of Common Stock or 
other securities, to be entitled, directly or indirectly through one or more 
intermediaries, to all material incidents of ownership with respect to such 
securities, including, but not limited to, (i) the right to vote such 
securities (in the case of voting securities), (ii) subject to any transfer 
restrictions, the right to dispose of such securities and to receive any 
proceeds realized from the 

                                       3



disposition thereof and (iii) the right to receive any dividends and other 
distributions with respect to such securities.

          The Common Directors shall be elected by the holders of Common 
Stock by a plurality vote and the Class B Directors shall be elected by the 
holders of the Class B Common Stock by a plurality vote, in either case at an 
annual stockholders meeting, except as hereinafter provided, and each 
director shall hold office until his successor has been duly elected and 
qualified or his earlier death, resignation or removal.  Vacancies in any 
class of directors and newly created directorships resulting from any 
increase in the authorized number of directors of any class of Company Common 
Stock may be filled by the majority of directors of such class then in 
office, though less than a quorum, or by a sole remaining director so elected 
and the directors so chosen shall hold office until the next annual election 
and until their successors are duly elected and shall qualify, or until their 
earlier death, resignation or removal.  If there are no directors in office, 
then an election of directors may be held in the manner provided by law.  If, 
at the time of filling any vacancy or any newly created directorship, the 
directors then in office shall constitute less than a majority of the whole 
Board (as constituted immediately prior to any such increase), the Court of 
Chancery may, upon application of any stockholder or stockholders holding at 
least ten percent (10%) of the total number of the shares at the time 
outstanding having the right to vote for such directors, summarily order an 
election to be held to fill any such vacancy or newly-created directorships, 
or to replace the directors chosen by the directors then in office.  Unless 
otherwise restricted by law, any director or the entire Board may be removed, 
with or without cause, by a majority vote of the class of Company Common 
Stock entitled to elect such director or directors.  No decrease in the size 
of the Board shall serve to shorten the term of an incumbent director.

          (c)  VOTING RIGHTS OF CLASS B COMMON STOCK.  The following actions 
shall require the approval of a majority of the outstanding Class B Common 
Stock, voting as a single class:

               (i)  the approval of any annual budget or business plan for
     the corporation or any subsidiary of the corporation or the deviation
     by the corporation or any such subsidiary from any annual budget for
     the corporation or such subsidiary approved by the Board of Directors
     by more than five percent (5%);

               (ii) issuance by the corporation of any equity securities,
     including securities convertible into equity securities (other than
     (A) the grant of employee stock options (subject to the proviso set
     forth in (D)

                                       4


     below), (B) the issuance of equity securities pursuant to
     the Purchase Agreement, dated as of  September  27, 1996 between the
     corporation and SBW (the "Purchase Agreement") or pursuant to any of
     the other Transaction Documents (as defined in the Purchase
     Agreement), (C) the issuance of equity securities upon the exercise or
     conversion of securities or employee stock options that are
     outstanding as of  September  27, 1996 or (D) the issuance of equity
     securities upon the conversion of Class B Common Stock or upon the
     exercise of employee stock options granted hereafter, PROVIDED,
     HOWEVER, that there shall not be outstanding at any time employee
     stock options for more than 1.5 million shares of Common Stock plus
     the options granted to William C. Kennedy, Jr. and William C. Saunders
     that are outstanding at  September  27, 1996) or incurrence of any
     indebtedness, provided that the corporation can incur up to $5 million
     in indebtedness in any year without the approval of the Class B Common
     Stock;

               (iii) the hiring or termination by the corporation of
     its chief executive officer, chief operating officer or chief
     financial officer;

               (iv) the corporation's entering into any line of business
     other than its Existing Line of Business (as hereinafter defined) or
     into any joint ventures, partnerships or similar arrangements; 

               (v)  the corporation's exiting its Existing Line of Business
     or disposing of assets (other than telecommunications equipment and
     other assets sold in the ordinary course of business) in any year with
     a value in excess of $500,000 or which are otherwise material to the
     corporation's operations;

               (vi) the adoption, implementation or acceptance (including
     the failure to opt out) of any Anti-Takeover Provision (as hereinafter
     defined) not in effect as of September 27, 1996 that would be
     applicable to, and, in the reasonable determination of SBW, adversely
     affect, the holders of the Class B Common Stock and their Affiliates;
     or

               (vii) the taking of any corporate action that would
     reduce the number of shares in the Reference Package below 1,600.

                                       5



          "Anti-Takeover Provision" means (i) any provision of the 
certificate of incorporation or bylaws of the corporation or any contract, 
agreement or plan to which the corporation is a party or by which it is bound 
or any statutory provision enacted after September 27, 1996 which is 
applicable to the corporation which the corporation may opt out of if the 
effect of such provision would be to materially delay, hinder or prevent a 
change in control of the corporation or (ii) a stockholder rights plan or 
"poison pill," including the provisions of any preferred stock or common 
stock purchase rights issued pursuant thereto; provided, however, that such 
term shall not include any customary change of control provisions contained 
in employment agreements between the corporation and any of its directors, 
officers or other employees or in any plans or agreements relating to stock 
options or other awards of equity securities made by the corporation to any 
such persons.  

          "Existing Line of Business" means a non-facilities based, enhanced 
service provider that offers fleet management and/or status or information 
about vehicles and/or location capabilities through mobile communications 
service.

          (d)  BYLAWS.   Any alteration, amendment, repeal or replacement of 
Article XI of the corporation's bylaws, or of any other Article of the bylaws 
that would have a similar effect, by the stockholders of the corporation 
shall require the approval of a majority of the outstanding Class B Common 
Stock, voting as a separate class.

          3.   CONVERSION

          (a)  OPTIONAL CONVERSION.  At the option of the holder thereof, 
each share of Class B Common Stock may be converted into the Reference 
Package; provided, however, that no shares of Class B Common Stock may be 
converted pursuant to this Section 3(a) unless the holders of all outstanding 
shares of Class B Common Stock elect to convert such shares into the 
Reference Package as of the same date in accordance with the procedures set 
forth below.

          (b)  OPTIONAL CONVERSION PROCEDURES.  Any holder of shares of Class 
B Common Stock desiring to convert such shares into Common Stock shall 
surrender the certificate or certificates evidencing such shares of Class B 
Common Stock, at the principal office of the corporation or such other office 
as the corporation may designate for such purpose, which certificate or 
certificates, if the corporation shall so require, shall be duly endorsed to 
the corporation or in blank, or accompanied by proper instruments of transfer 
to the corporation or in blank, accompanied by irrevocable written notice to 
the corporation that the holder elects so to convert such shares of Class B 
Common Stock and specifying 

                                       6



the name or names (with address or addresses) in which a certificate or 
certificates evidencing shares of Common Stock are to be issued.  The 
corporation shall, as soon as practicable after such surrender of 
certificates evidencing shares of Class B Common Stock accompanied by the 
written notice and compliance with any other conditions herein contained, 
deliver by first class mail postage prepaid to the holder that surrendered 
such shares of Class B Common Stock or to such holder's nominee certificates 
evidencing the number of full shares of Common Stock to which such holder 
shall be entitled as aforesaid, together with a cash adjustment in respect of 
any fraction of a share of Common Stock as provided below.  No interest will 
be payable with respect to any cash adjustment paid with respect to any 
fractional shares of Common Stock as provided below.  On the date shares of 
Class B Common Stock are surrendered for conversion, dividends shall cease to 
accrue on all shares of Class B Common Stock, such shares shall no longer be 
deemed outstanding, all rights of the holders thereof as holders of Class B 
Common Stock shall cease (other than the right to receive dividends declared 
payable to holders of record of Class B Common Stock on a record date prior 
to the date of surrender) and thereupon the certificate or certificates 
theretofore representing such shares of Class B Common Stock shall represent 
only the right to receive the Common Stock deliverable upon conversion in 
respect thereof.

          (c)  FRACTIONAL SHARES; TAXES.  No fractional shares or scrip 
representing fractional shares shall be issued upon the conversion of Class B 
Common Stock.  If any such conversion would otherwise require the issuance of 
a fractional share, an amount equal to such fraction multiplied by the 
Closing Price of the Common Stock on the day of conversion shall be paid to 
the holder in cash by the Corporation.  The term "Closing Price" on any day 
shall mean 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.  The corporation will pay any and all stamp taxes, stock 
issuance taxes or similar taxes that may be payable in respect of the 
issuance or delivery of Common Stock on conversion of shares of Class B 
Common Stock; provided, however, that the corporation shall not be required 
to pay any tax or other charge that may be payable in respect of any transfer 
involved in the issuance and delivery of any certificate in a name 

                                       7



other than that of the record holder of the shares of Class B Common Stock 
being converted and in such case the corporation shall not be obligated to 
issue or deliver any stock certificate until such tax or charge has been paid 
in full or it has been established to the satisfaction of the corporation 
that no such tax or charge is due.

          (d)  AVAILABLE COMMON STOCK.  The corporation shall at all times 
reserve and keep available out of its authorized but unissued Common Stock, 
for the purpose of issuance upon conversion of Class B Common Stock, the full 
number of Common Stock then deliverable upon the conversion of all shares of 
Class B Common Stock then outstanding.

          4.   TRANSFER

          (a)  PROHIBITED TRANSFERS.  No holder of shares of Class B Common 
Stock shall Transfer any such shares or any interest therein to any Person 
(as hereinafter defined) other than SBW or an Affiliate of SBW.  As used 
herein, the term "Transfer" means any sale, transfer, assignment, disposition 
or other means of conveying legal or beneficial ownership of such shares, 
whether direct or indirect and whether voluntary or involuntary, and the 
terms "Transferred," "Transferable," "Transferor" and "Transferee" have 
correlative meanings.  As used herein, the term "Person" means any 
individual, corporation, partnership, joint stock company, joint venture, 
association, trust, unincorporated organization, government or any agency, 
department or political subdivision thereof, or any other entity.

          (b)  EFFECT OF PURPORTED TRANSFERS.  Any attempted or purported 
Transfer of shares of Class B Common Stock in violation of paragraph (a) 
above shall not be effective to Transfer ownership of such shares to the 
purported Transferee thereof, who shall not be entitled to any rights as a 
stockholder of the corporation with respect to the shares purported to be 
Transferred (including, but not limited to, the right to vote such shares or 
to receive dividends with respect thereto).  All rights with respect to any 
shares attempted or purported to be Transferred in violation of the 
aforementioned provisions shall remain the property of the stockholder who 
initially attempted or purported to transfer such shares in violation 
thereof.  Upon a determination by the Board of Directors that there has been 
or is threatened an attempted or purported Transfer of shares in violation of 
the aforementioned provisions, the Board of Directors may take such action as 
it deems advisable, including but not limited to refusing to give effect on 
the books of the corporation to such attempted or purported Transfer or 
instituting legal proceedings to enjoin or rescind the same.

                                       8



          (c)  LEGEND.  All certificates evidencing shares of this Series 
shall bear a conspicuous legend referencing the restrictions set forth in 
this Section 4.

                               B.  PREFERRED STOCK

          The Board of Directors of the corporation, by resolution or 
resolutions, may at any time and from time to time, divide and establish any 
or all of the unissued shares of Preferred Stock not then allocated to any 
series of Preferred Stock into one or more series and, without limiting the 
generality of the foregoing, fix and determine the designation of each such 
share, the number of shares which shall constitute such series and certain 
powers, preferences and relative, participating, optional or other special 
rights and qualifications, limitations and restrictions and voting rights of 
the shares of each series so establishing.

                       SERIES D PARTICIPATING CONVERTIBLE
                                 PREFERRED STOCK

          1.   DESIGNATION AND AMOUNT.  The distinctive serial designation of 
this series shall be "Series D Participating Convertible Preferred" 
(hereinafter sometimes referred to as "this Series").  The number of shares 
in this Series shall be 1,000, which number may be decreased (but not 
increased) by the Board of Directors of the corporation (the "Board of 
Directors") without a vote of stockholders; PROVIDED, HOWEVER, that such 
number may not be decreased below the number of then currently outstanding 
shares of this Series.

          2.   DIVIDENDS.  (a) The holders of shares of this Series shall be 
entitled to receive, when and as declared by the Board of Directors, but only 
out of funds legally available therefor, dividends and distributions, on each 
date that dividends or other distributions (other than dividends or 
distributions payable in Common Stock (as defined below)) are payable on or 
in respect of Common Stock in an amount per share of this Series equal to the 
aggregate amount of dividends or other distributions (other than dividends or 
distributions payable in Common Stock of the corporation) that would be 
payable on such date to a holder of the Reference Package.  Each such 
dividend and distribution shall be paid to the holders of record of shares of 
this Series on the date, not exceeding sixty days preceding such dividend or 
distribution payment date, fixed for the purpose by the Board of Directors in 
advance of payment of each particular dividend or distribution.  

          (b)  The term "Reference Package" shall initially mean 1,600 shares 
of Common Stock.  In the event the corporation shall at any time after the 
close of business on  September  27, 1996 (A) declare or pay a dividend on 
any Common Stock payable in 

                                       9



Common Stock, (B) subdivide any Common Stock or (C) combine any Common Stock 
into a smaller number of shares or (D) change or reclassify the Common Stock 
(whether pursuant to a merger or consolidation or otherwise), then and in 
each such case the Reference Package after such event shall be the Common 
Stock, or new class of shares, that a holder of the Reference Package 
immediately prior to such event would hold thereafter as a result thereof.

          3.   LIQUIDATION PREFERENCE.  (a) In the event of any liquidation, 
dissolution or winding up of the affairs of the corporation, whether 
voluntary or involuntary, the holders of shares of this Series shall be 
entitled, before any distribution or payment is made on any date to the 
holders of the Common Stock or any other stock of the corporation ranking 
junior to this Series upon liquidation, to be paid in full an amount per 
share of this Series equal to the greater of (A) $20,000 or (B) the aggregate 
amount distributed or to be distributed prior to such date in connection with 
such liquidation, dissolution or winding up to a holder of the Reference 
Package (such greater amount being hereinafter referred to as the 
"Liquidation Preference"), together with accrued dividends to such 
distribution or payment date, whether or not earned or declared.  If such 
payment shall have been made in full to all holders of shares of this Series, 
the holders of shares of this Series as such shall have no right or claim to 
any of the remaining assets of the corporation.

          (b)  In the event the assets of the corporation available for 
distribution to the holders of shares of this Series upon any liquidation, 
dissolution or winding up of the corporation, whether voluntary or 
involuntary, shall be insufficient to pay in full all amounts to which such 
holders are entitled pursuant to paragraph (a) of this Section 3, no such 
distribution shall be made on account of any shares of any other class or 
series of Preferred Stock ranking on a parity with the shares of this Series 
upon such liquidation, dissolution or winding up unless proportionate 
distributive amounts shall be paid on account of the shares of this Series, 
ratably in proportion to the full distributable amounts for which holders of 
all such parity shares are respectively entitled upon such liquidation, 
dissolution or winding up.

          (c)   For the purposes of this Section 3, the consolidation or 
merger of, or binding share exchange by, the corporation with any other 
corporation or the sale of all or substantially all the assets of the 
corporation shall not be deemed to constitute a liquidation, dissolution or 
winding up of the corporation.

          4.   CONVERSION PRIVILEGE.  (a) Subject to and upon compliance with 
the provisions of this Section 4, at the option of the holder of shares of 

                                       10



this Series, shares of this Series may be converted, in blocks of 250 shares 
or any larger integral multiple thereof.  Such conversion right shall 
commence at the opening of business on September 30, 1996.

          (b)  Subject to subsection (a) hereof, each share of this Series 
shall be convertible into the Reference Package.

          (c)  The Board of Directors may make such adjustments in the 
Reference Package, in addition to those required by Section 2(b), as shall be 
determined by the Board, as evidenced by a Board resolution, to be necessary 
and advisable in order to avoid taxation so far as practicable of any 
dividend of stock or stock rights or any event treated as such for Federal 
income tax purposes to the recipients.

          (d)  Whenever any adjustment is required in the Reference Package, 
the corporation shall forthwith (i) file at the principal office of the 
corporation a statement describing in reasonable detail the adjustment and 
the method of calculation used, and (ii) cause a copy of such statement to be 
mailed by first class mail postage prepaid to the holders of record of this 
Series as of the effective date of such adjustment.

          (e)  The corporation shall at all times reserve and keep available 
out of its authorized but unissued Common Stock, for the purpose of issuance 
upon conversion of this Series, the full number of Common Stock then 
deliverable upon the conversion of all shares of this Series then outstanding.

          (f)  The corporation will pay any and all stamp taxes, stock 
issuance taxes or similar taxes that may be payable in respect of the 
issuance or delivery of Common Stock on conversion of shares of this Series; 
provided, however, that the corporation shall not be required to pay any tax 
or other charge that may be payable in respect of any transfer involved in 
the issuance and delivery of any certificate in a name other than that of the 
record holder of the shares of this Series being converted and in such case 
the corporation shall not be obligated to issue or deliver any stock 
certificate until such tax or charge has been paid in full or it has been 
established to the satisfaction of the corporation that no such tax or charge 
is due.

          (g)  No fractional shares or scrip representing fractional shares 
shall be issued upon the conversion of this Series.  If any such conversion 
would otherwise require the issuance of a fractional share, an amount equal 
to such fraction multiplied by the Closing Price of the Common Stock on the 
day of conversion shall be paid to the holder in cash by the corporation.  
The term "Closing Price" on any day shall mean the reported last sale price 
per share of Common Stock regular way on such day or, in case no such sale 

                                       11



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.

          (h)  The corporation may obtain the certificate of any independent 
firm of public accountants of national recognition selected by the Board of 
Directors, which, if obtained, shall be presumptive evidence of the 
correctness of any computation made under Section 2(b).

          (i)  All shares of this Series surrendered for conversion or 
otherwise acquired by the corporation shall be cancelled and thereupon 
restored to the status of authorized but unissued preferred stock 
undesignated as to series.

          5.   CONVERSION PROCEDURES.  (a) Any holder of shares of this 
Series desiring to convert such shares into Common Stock shall surrender the 
certificate or certificates evidencing such shares of this Series together 
with instructions setting forth the number of shares to be converted, at the 
principal office of the corporation or such other office as the corporation 
may designate for such purpose, which certificate or certificates, if the 
corporation shall so require, shall be duly endorsed to the corporation or in 
blank, or accompanied by proper instruments of transfer to the corporation or 
in blank, accompanied by irrevocable written notice to the corporation that 
the holder elects so to convert such shares of this Series and specifying the 
name or names (with address or addresses) in which a certificate or 
certificates evidencing shares of Common Stock are to be issued.

          (b)  The corporation shall, as soon as practicable after such 
surrender of certificates evidencing shares of this Series accompanied by the 
written notice and compliance with any other conditions herein contained, 
deliver by first class mail postage prepaid to the Person that surrendered 
such shares of this Series or to such Person's nominee certificates 
evidencing the number of full shares of Common Stock to which such Person 
shall be entitled as aforesaid, together with a cash adjustment in respect of 
any fraction of a share of Common Stock as provided above.  No interest will 
be payable with respect to any cash adjustment paid with respect to any 
fractional shares of Common Stock as provided above.

                                       12



          (c)  In the event that fewer than all shares of Series D 
Participating Convertible Preferred represented by a surrendered certificate 
are to be converted hereunder, a new certificate shall be issued at the 
expense of the corporation representing the shares of Series D Participating 
Convertible Preferred not so converted.

          (d)  On the date shares of Series D Participating Convertible 
Preferred are surrendered for conversion, dividends shall cease to accrue on 
any shares of this Series surrendered for conversion, such shares shall no 
longer be deemed outstanding, all rights of the holders thereof as preferred 
stockholders of the corporation shall cease (other than the right to receive 
dividends declared payable to holders of record of this Series on a record 
date prior to the date of surrender) and thereupon the certificate or 
certificates theretofore representing such shares of Series D Participating 
Convertible Preferred shall represent only the right to receive the Common 
Stock deliverable upon conversion in respect thereof.

          6.   MANDATORY CONVERSION.  (a) If the Regulatory Relief Date shall 
not have occurred on or before  September  27, 2001, all of the then 
currently outstanding shares of Series D Participating Convertible Preferred 
shall, at the election of the corporation at any time after the opening of 
business on September 28, 2001 and after notice has been provided as set 
forth below, be converted into shares of Common Stock on the basis provided 
in Section 4.

          (b)  If the corporation has elected to convert this Series into 
Common Stock pursuant to this Section 6, the corporation will provide notice 
of mandatory conversion of shares of Series D Participating Convertible 
Preferred pursuant to this Section 6 to holders of record of the Series D 
Participating Convertible Preferred to be converted not less than 15 nor more 
than 60 days prior to the date fixed for conversion.  Such notice shall be 
provided by mailing notice of such conversion first class mail postage 
prepaid, to each holder of record of the Series D Participating Convertible 
Preferred to be converted, at such holder's address as it appears on the 
stock register of the corporation.

          (c)  Effective on the conversion date fixed by the corporation and 
notified to the holders of Series D Participating Convertible Preferred 
pursuant to subparagraph (b) of this Section 6, each outstanding share of 
Series D Participating Convertible Preferred shall be converted into fully 
paid and nonassessable shares of Common Stock on the basis provided in 
Section 4, automatically and without any action on the part of any holder of 
shares of Series D Participating Convertible Preferred, and such shares of 
Common Stock shall be deemed outstanding from and after such conversion date.

                                       13



          (d)  As of the Regulatory Relief Date, each share of this Series 
shall automatically, without any action on the part of the holder thereof, 
convert into one share of Class B Common Stock, and as of such date, the 
holders thereof shall be treated in all respects as the holders of Class B 
Common Stock.

          (e)  Each holder of shares of Series D Participating Convertible 
Preferred to be converted pursuant to Section 6(a) and 6(d) shall surrender 
the certificates evidencing such shares to the corporation at the principal 
office of the corporation, and shall thereupon be entitled to receive 
certificates evidencing shares of Common Stock and to receive any dividends 
or other distributions payable on shares of Common Stock payable following 
such surrender to the holders of record after the date of such conversion and 
any cash payable in lieu of fractional shares.

          7.   PROVISIONS IN CASE OF CONSOLIDATION OR MERGER.  In case of any 
consolidation of the corporation with, or merger of the corporation into, any 
other Person or any merger of another Person into the corporation (other than 
a merger which does not result in any reclassification, conversion, exchange 
or cancellation of outstanding shares of Common Stock of the corporation), 
the Person formed by such consolidation or resulting from such merger, as the 
case may be, shall provide for the conversion of each share of this Series 
into the kind and amount of securities, cash and other property receivable 
upon such consolidation or merger by a holder of the number of shares of 
Common Stock of the corporation into which such share of this Series might 
have been converted immediately prior to such consolidation or merger, 
assuming such holder of Common Stock of the corporation (i) is not a Person 
with which the corporation consolidated or into which the corporation merged 
or which merged into the corporation, as the case may be ("Constituent 
Person"), or an Affiliate of a Constituent Person and (ii) failed to exercise 
his rights of election, if any, as to the kind or amount of securities, cash 
and other property receivable upon such consolidation or merger (provided 
that if the kind or amount of securities, cash and other property receivable 
upon such consolidation or merger is not the same for each share of Common 
Stock of the corporation held immediately prior to such consolidation or 
merger by others 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 7 the kind and 
amount of securities, cash and other property receivable upon such 
consolidation or merger 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).  If as a result of the provisions of this Section 7 the shares of 
this Series become convertible or exchangeable into securities or assets of a 
Constituent Person, such Constituent Person shall provide for adjustments 
which, for events subsequent to the effective date of such consolidation, 
merger or sale of assets, shall be as nearly equivalent as may be practicable 

                                       14



to the adjustments provided for herein.  The above provisions of this Section 
7 shall similarly apply to successive consolidation or mergers.

          8.   REDEMPTION.  The shares of this Series shall not be redeemable.

          9.   VOTING RIGHTS.  (a) Except as required by law or as provided 
in Section 9(b) below, the holders of shares of this Series shall not be 
entitled to vote on any matter submitted to the stockholders of the 
corporation.

          (b)  In addition to any vote of this Series which may be required 
by law, the affirmative vote of a majority of the outstanding shares of the 
Series D Participating Convertible Preferred, voting as a class, shall be 
required to approve the following:

               (i)  any merger or consolidation of the corporation with or
     into any other Person that requires a vote of the stockholders of the
     corporation in accordance with the applicable provisions of the
     General Corporation Law of the State of Delaware;

               (ii) any sale or transfer of all or substantially all of the
     assets of the corporation that requires a vote of the stockholders of
     the corporation in accordance with the applicable provisions of the
     General Corporation Law of the State of Delaware;

               (iii) any amendment, alteration or repeal of the
     corporation's Certificate of Incorporation, as amended;

               (iv) the dissolution of the corporation;

               (v)  the adoption, implementation or acceptance (including
     the failure to opt out) of any Anti-Takeover Provision not in effect
     as of September 27, 1996 that would be applicable to, and, in the
     reasonable determination of the holders of this Series, adversely
     affect, the holders of this Series and their Affiliates;

               (vi) issuance by the corporation of any equity securities,
     including securities convertible into equity securities (other than
     (A) the grant of employee stock options (subject to the proviso set
     forth in (D) below), (B) the issuance of equity securities pursuant to
     the Purchase Agreement or any of the other Transaction Documents, (C)
     the issuance of 
                                       15



     equity securities upon the exercise or conversion of
     securities or employee stock options that are outstanding as of 
     September 27, 1996, or upon the conversion of shares of this Series,
     or (D) the issuance of equity securities upon the exercise of employee
     stock options granted after September 27, 1996, PROVIDED, HOWEVER,
     that there shall not be outstanding at any time employee stock options
     for more than 1.5 million shares of Common Stock plus the options
     granted to William C. Kennedy, Jr. and William C. Saunders that are
     outstanding at  September 27, 1996) or incurrence of any indebtedness
     for borrowed money or evidenced by bonds, notes or debentures,
     provided that the corporation can incur up to $5 million in
     indebtedness in any one year without a vote of this Series;

               (vii)  the corporation's entering into any line of
     business other than its Existing Line of Business or entering into
     joint ventures, partnerships or similar arrangements, which, in each
     such case, would require expenditures, individually or in the
     aggregate, of more than $3 million;

               (viii) any disposal or disposition in any 12-month period
     of any asset or assets of the corporation (other than
     telecommunications equipment and other assets sold in the ordinary
     course of business) of which the sale, or fair market value exceeds in
     the aggregate $3 million;

               (ix) any amendment, alteration or repeal of the terms of
     this Series including, without limitation, any increase in the number
     of authorized shares of such series; and

               (x)  any corporate action that would reduce the number of
     shares in the Reference Package below 1,600.

          10.  TRANSFER.

          (a)  PROHIBITED TRANSFERS.  No holder of shares of this Series 
shall Transfer any such shares or any interest therein to any Person other 
than SBW or an Affiliate of SBW. 

          (b)  EFFECT OF PURPORTED TRANSFERS.  Any attempted or purported 
Transfer of shares of this Series in violation of paragraph (a) above shall 
not be effective to Transfer ownership of such shares to the purported 
Transferee thereof, who shall not be entitled to 

                                       16



any rights as a stockholder of the corporation with respect to the shares 
purported to be Transferred (including, but not limited to, the right to vote 
such shares or to receive dividends with respect thereto).  All rights with 
respect to any shares attempted or purported to be Transferred in violation 
of the aforementioned provisions shall remain the property of the Person who 
initially attempted or purported to transfer such shares in violation 
thereof.  Upon a determination by the Board of Directors that there has been 
or is threatened an attempted or purported Transfer of shares in violation of 
the aforementioned provisions, the Board of Directors may take such action as 
it deems advisable, including, but not limited to, refusing to give effect on 
the books of the corporation to such attempted or purported Transfer or 
instituting legal proceedings to enjoin or rescind the same.

          (c)  LEGEND.  All certificates evidencing shares of this Series 
shall bear a conspicuous legend referencing the restrictions set forth in 
this Section 10.

          11.  DEFINITIONS.  As used herein, the following terms shall have 
the following meanings unless the context otherwise requires.

          "Purchase Agreement" means the Purchase Agreement, dated as of 
September 27, 1996, between the corporation and SBW.

          "Regulatory Relief Date" shall mean that date on which SBC 
Communications, Inc. or its Affiliates have, in their sole judgment, obtained 
all necessary federal and state regulatory approvals to provide landline, 
interLATA long-distance service pursuant to the Communications Act of 1934, 
as amended by the Telecommunications Act of 1996.

          SECOND:  That thereafter the necessary number of shares as required 
by statute were voted in favor of the amendments.

          THIRD:  That said amendments were duly adopted in accordance with 
the provisions of Sections 228 and 242 of the General Corporation Law of the 
State of Delaware.

                                       17



          IN WITNESS WHEREOF, HighwayMaster Communications, Inc. has made 
under its corporate seal and the hands of its President and Secretary, 
respectively, of such corporation the foregoing certificate, and the said 
President and Secretary have hereunto set their hands and caused the 
corporate seal of such corporation to be hereunto affixed this ___th day of 
__________, 1996.

                         HIGHWAYMASTER COMMUNICATIONS, INC.



                         By: 
                             -------------------------------------
                             President


ATTEST:



- -------------------------------
 Secretary

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