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                                                                  EXHIBIT 10.21

                              EMPLOYMENT AGREEMENT


         This Employment Agreement (this "AGREEMENT"), dated and effective as
of the 3rd day of June, 1998, is entered into in Dallas, Texas by and between
HighwayMaster Corporation, a Delaware corporation, with its principal place of
business located at 16479 Dallas Parkway, Suite 710, Dallas, Texas, 75248
("EMPLOYER"), and William H. McCausland, an individual residing in Dallas,
Texas ("EMPLOYEE").

         NOW, THEREFORE, in consideration of the mutual covenants set forth
herein, Employer and Employee, intending to be legally bound, hereby agree as
follows:

         1. Employment Relationship. Employer hereby employs Employee, and
Employee hereby accepts such employment, upon the terms and conditions set
forth in this Agreement. Such employment relationship shall continue for the
stated term of this Agreement, as described in Section 8 hereof, or until the
earlier termination of such relationship and this Agreement pursuant to Section
6 hereof.

         2. Position and Responsibilities of Employee. Employee shall be
employed as Sr. Vice President, Network and Customer Operations, with job
responsibilities related thereto and to be expanded at the sole discretion of
Employer. Employee shall report to the President and shall devote such time and
attention to the business of Employer as shall be required for the efficient
management thereof, and shall manage and supervise such business, and shall
devote his full time best efforts to the faithful performance of his duties on
behalf of Employer. Employee shall also perform such other duties, and may have
job responsibilities and titles modified from time to time as may be requested
by the President or by resolution of the Board of Directors of Employer,
provided such duties and job titles are generally consistent with the level of
responsibility currently held by Employee. Employee shall not engage in
additional gainful employment during the term of this Agreement without advance
written consent from Employer.

         3. Compensation. For all services rendered by Employee pursuant to
this Agreement, Employer shall pay to Employee, and Employee shall accept as
full compensation hereunder the following:

            (a) Salary. Employee shall receive a salary of $12,500 per month
         payable by Employer in bi-monthly amounts in Dallas, Texas. Employee's
         salary shall be subject to all appropriate federal and state
         withholding taxes and shall be payable in accordance with the normal
         payroll procedures of Employer. Employer may be permitted in its sole
         discretion, but not required, to increase the amount of compensation
         payable to Employee during the term of this Agreement, however, once
         increased the compensation may not be decreased.

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            (b) Benefits and Perquisites. Employee shall be entitled to
         participate in the employee benefit plans provided by Employer for all
         employees generally, and for executive employees of Employer. Employer
         shall be entitled to change such plans from time to time, and the
         parties acknowledge that at the initial date of this Agreement the
         fringe benefits provided to Employee include a corporate 401(k) plan
         (contributions by Employee only), health and dental insurance for the
         Employee, and reimbursement of certain expenses in accordance with the
         policies and procedures of the Company.

            (c) Discretionary Bonuses. Employer shall establish an incentive
         bonus plan for Employee based on various targets and performance
         criteria to be established by the President and Board of Directors in
         consultation with the Employee. The evaluation of the performance of
         the Employee as measured by the applicable targets and the awarding of
         applicable bonuses, if any, shall be at the sole discretion of the
         President. The potential annual bonus which may be awarded to Employee
         shall be in the amount of $25,000 two times during each fiscal year of
         Employer (for a potential total of $50,000 per fiscal year), during
         the term of this Agreement. Each annual discretionary bonus may be
         awarded in whole, in part, or withheld in its entirety based on the
         level of incentive bonus plan performance criteria achieved by
         Employee, in the sole judgement of the President and Board of
         Directors. The discretion allowed the President, in this paragraph is
         expressly made subject to the duty of good faith and fair dealing set
         forth below in Paragraph 13.

         4. Stock Options. Employee previously has been issued stock options to
purchase shares of stock of HighwayMaster Communications, Inc. The terms of the
stock options are as set forth in the applicable Employee Stock Option Plan and
Employee Stock Option Agreement previously signed by the Employee.
Notwithstanding the terms of the Stock Option Agreement dated as of September
18, 1998 between Employee and HighwayMaster Communications, Inc. (the "1998
Stock Option Grant"), in the event that 50% or more of the outstanding common
stock or assets of the Employer are sold or otherwise transferred for reasons
other than merely administrative reorganization ("Change in Control of the
Company"), all stock options issued pursuant to the 1998 Stock Option Grant
shall accelerate and be deemed vested on the day prior to the Change in Control
of the Company.

         5. Protective Covenants. Employee recognizes that his employment by
Employer is one of the highest trust and confidence because (i) Employee will
become fully familiar with all aspects of Employer's business during the period
of his employment with Employer, (ii) certain information of which Employee
will gain knowledge during his employment by Employer is proprietary and
confidential information which is of special and peculiar value to Employer,
and (iii) if any such proprietary and confidential information were imparted to
or became known by any person, including Employee, engaging in a business in
competition with that of Employer, hardship, loss and irreparable injury and
damage could result to Employer, the measurement of which would be difficult if
not impossible to ascertain. Employee acknowledges that any and all inventions,
improvements, discoveries, formulae, processes, products or designs developed
by Employee alone or in conjunction with others in connection with Employer's
business during the term of Employee's employment with Employer ("Proprietary
Information") shall be the sole and absolute property of Employer in

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perpetuity, that Employee shall promptly disclose such Proprietary Information
to Employer, and Employee shall have no right, title or interest therein or to
receive additional monies therefor, regardless of whether development occurred
during working hours or any other time during the term of Employee's employment
with Employer. Employee shall assist Employer in obtaining patents on all such
Proprietary Information deemed patentable by Employer and shall execute all
documents necessary to obtain such patents and to vest Employer with full and
exclusive title to the patents and to provide testimony, documents, or
otherwise make himself available to protect the patents against infringement by
others. For purposes of this Agreement, an invention shall be deemed to have
been made during the period of Employee's employment if, during such period,
the invention was conceived or first actually reduced to practice, and Employee
agrees that any patent application filed by Employee within one (1) year after
the termination of Employee's employment with Employer shall be presumed to
relate to an invention made during the term of Employee's employment with
Employer unless Employee can establish the contrary. Employee further
acknowledges that Employer has developed unique skills, concepts, sales
presentations, marketing programs, marketing strategy, business practices,
methods of operation, trademarks, licenses, technical information, Proprietary
Information, computer software programs, tapes and discs concerning its
operations systems, customer lists, customer leads, documents identifying past,
present and future customers, hiring and training methods, investment policies,
financial and other confidential and proprietary information concerning its
operations and expansion plans ("Trade Secrets"). Therefore, Employee agrees
that it is necessary for Employer to protect its business and that of its
affiliates from such damage, and Employee further agrees that the following
covenants constitute a reasonable and appropriate means, consistent with the
best interest of both Employee and Employer, to protect Employer or its
affiliates against damage due to loss or disclosure of Proprietary Information
or Trade Secrets and shall apply to and be binding upon Employee as provided
herein:

            (a) Trade Secrets. Employee recognizes that his position with
         Employer is one of the highest trust and confidence by reason of
         Employee's access to and contact with certain Trade Secrets of
         Employer. Employee agrees and covenants that, except as may be
         required by Employer in connection with this Agreement, or with the
         prior written consent of Employer, Employee shall not, either during
         the term of this Agreement or thereafter, directly or indirectly, use
         for Employee's own benefit or for the benefit of another, or disclose,
         disseminate, or distribute to another, except as directed by Employer
         or as required for the performance of Employee's duties on behalf of
         the Employer, any Trade Secret (whether or not acquired, learned,
         obtained, or developed by Employee alone or in conjunction with
         others) of Employer or of others with whom Employer has a business
         relationship. All memoranda, notes, records, drawings, documents, or
         other writings whatsoever made, compiled, acquired, or received by
         Employee during the term of this Agreement, arising out of, in
         connection with, or related to any activity or business of Employer,
         including, but not limited to, the customers, suppliers, or others
         with whom Employer has a business relationship, the arrangements of
         Employer with such parties, and the pricing and expansion policies and
         strategy of Employer, are, and shall continue to be, the sole and
         exclusive property of Employer and shall, together with all copies
         thereof and all advertising literature, be returned and delivered to
         Employer by Employee immediately, without demand, upon the termination
         of this Agreement, or at any time upon Employer's demand.

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            Employee represents and warrants that he is not bound by any
         agreement with any prior employer or other party that will be breached
         by execution and performance of this Agreement, or which would
         otherwise prevent him from performing his duties with Employer as set
         forth in this Agreement. Employee represents and warrants that he has
         not retained any copies of proprietary and confidential information of
         any prior employer, and he will not use or rely on any confidential
         and proprietary information of any prior employer in carrying out his
         duties for Employer.

            (b) Covenant Not to Compete. In the event this Agreement is
         terminated for any reason, Employee hereby covenants and agrees that
         for a period of 24 months after termination of this Agreement for any
         reason, he will not directly or indirectly, either as an employee,
         employer, consultant, agent, principal, partner, shareholder (other
         than through ownership of publicly-traded capital stock of a
         corporation which represents less than five percent (5%) of the
         outstanding capital stock of such corporation), corporate officer,
         director, investor, financier or in any other individual or
         representative capacity, engage or participate in the wireless
         tracking and communication services business for the long haul
         trucking industry in the United States of America, or in wireless
         automotive vehicle security and roadside assistance services in the
         United States of America.

            (c) Survival of Covenants. Each covenant of Employee set forth in
         this Section 5 shall survive the termination of this Agreement and
         shall be construed as an agreement independent of any other provision
         of this Agreement, and the existence of any claim or cause of action
         of Employee against Employer whether predicated on this Agreement or
         otherwise shall not constitute a defense to the enforcement by
         Employer of said covenant.

            (d) Remedies. In the event of breach or threatened breach by
         Employee of any provision of this Section 5, Employer shall be
         entitled to relief by temporary restraining order, temporary
         injunction, or permanent injunction or otherwise, in addition to other
         legal and equitable relief to which it may be entitled, including any
         and all monetary damages which Employer may incur as a result of said
         breach, violation or threatened breach or violation. Employer may
         pursue any remedy available to it concurrently or consecutively in any
         order as to any breach, violation, or threatened breach or violation,
         and the pursuit of one of such remedies at any time will not be deemed
         an election of remedies or waiver of the right to pursue any other of
         such remedies as to such breach, violation, or threatened breach or
         violation, or as to any other breach, violation, or threatened breach
         or violation.

         Employee hereby acknowledges that Employee's agreement to be bound by
the protective covenants set forth in this Section 5 was a material inducement
for Employer entering into this Agreement and agreeing to pay Employee the
compensation and benefits set forth herein.

         6. Termination. The employment relationship between Employee and
Employer created hereunder shall terminate before the expiration of the stated
term of this Agreement upon the occurrence of any one of the following events:

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            (a) Death or Permanent Disability. The employment relationship
         shall be terminated effective on the death of the Employee.

            The Employee shall be entitled to leaves of absence from the
         Company in accordance with the policy of the Company generally
         applicable to executives for illness or other temporary disabilities
         for a period or periods not exceeding six months in any calendar year,
         and his status as an employee shall continue during such periods.
         Provided, that Employee shall apply for Employer's short term
         disability insurance payments during such six month period, Employer
         shall supplement such short term disability payments during the first
         three months of such six month period to equal Employee's total
         compensation under this Agreement, and during the last three months of
         such six month period Employee shall accept payments under the
         Employer's standard short term disability plan (as referenced in
         Section 3(b) above) in lieu of salary amounts set forth in Sections
         3(a) above. If, as a result of Employee's incapacity due to physical
         or mental illness which prevents Employee from satisfactorily
         performing duties for the Company on a full time basis and such
         incapacity is determined to be total and permanent such that the
         Employee will have been unable to perform her duties on a full-time
         basis for six months during a single fiscal year, the Employee shall
         be deemed to have experienced a permanent disability and the Company
         may terminate this Agreement upon thirty days written notice. If
         Employer terminates this Agreement pursuant to this sub-section,
         Employee shall be entitled to the compensation as specifically
         provided in Section 7 below.

            (b) Termination for Cause. The following events, which for purposes
         of this Agreement shall constitute "cause" for termination:

                (1) The willful breach by Employee of any provision of Sections
            1, 2 or 5 (including but not limited to a refusal to follow lawful
            directives of the Senior Management or Board of Directors of
            Employer which are not inconsistent with the provisions of this
            Agreement) after notice to Employee of the particular details
            thereof and a period of 10 days thereafter within which to cure
            such breach and the failure of Employee to cure such breach within
            such 10 day period;

                (2) Any act of fraud, misappropriation or embezzlement by
            Employee with respect to any aspect of Employer's business;

                (3) The illegal use of drugs by Employee during the term of
            this Agreement that, in the determination of the Senior Management
            of Employer, substantially interferes with Employee's performance
            of his duties hereunder;

                (4) Substantial failure by Employee to perform the fundamental
            functions and obligations of his employment position set forth in
            Section 2 of this Agreement, other than a failure permitted
            pursuant to Subsection 6(a) above, which is repeated or continued
            after 30 day written notice to Employee of such failure, and which
            is

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            materially injurious to the business or interests of Employer and
            which failure is not cured by Employee within such 30 day period;
            or

                (5) conviction of Employee by a court of competent jurisdiction
            of a felony or of a crime involving moral turpitude.

            Any notice of discharge under Section 6(a) or 6(b) above shall
         describe with reasonable specificity the cause or causes for the
         termination of Employee's employment, as well as the effective date of
         the termination (which effective date may be the date of such notice
         under Subsection 6(a) or 6(b) above). If Employer terminates
         Employee's employment for any of the reasons set forth above, Employer
         shall have no further obligations hereunder from and after the
         effective date of termination (other than as set forth below) and
         shall have all other rights and remedies available under this or any
         other agreement and at law or in equity.

            (c) Termination by Employee. Employee may terminate this Agreement
         without liability to Employer arising from the resignation of Employee
         at any time during the term of this Agreement upon 90 days or more
         (the "Notice Period") written notice to Employer. In the event of a
         proper notice by Employee, the termination date of Employee's
         employment and this Agreement with Employer shall be the date provided
         in such notice, and Employee shall be entitled to compensation during
         the Notice Period (ending in its entirety upon completion of the
         Notice Period), as provided in Section 7 below. Upon proper notice of
         Employee's voluntary termination, Employer has the right to require
         Employee to cease his employment responsibilities immediately;
         however, for purposes of the compensation, stock option vesting, and
         all other benefits provided to Employee by or as a result of this
         Agreement, Employee shall be considered an employee of Employer for
         the entire Notice Period.

            (d) Termination by Employer with Notice. Employer may terminate
         this Agreement without cause at any time upon 30 days' written notice
         to Employee, during which period Employee shall not be required to
         perform any services for Employer other than to assist Employer in
         training his successor and generally preparing for an orderly
         transition; PROVIDED, HOWEVER, that Employee shall be entitled to
         compensation upon such termination as provided in Section 7 below.

         7. Compensation Upon Termination. Upon the termination of Employee's
employment under this Agreement before the expiration of the stated term hereof
for any reason, Employee shall be entitled to (i) the salary earned by him
before the effective date of termination as provided in Section 3(a) hereof
(including salary payable during any applicable notice period), prorated on the
basis of the number of full days of service rendered by Employee during the
salary payment period to the effective date of termination, (ii) any accrued,
but unpaid, vacation or sick leave benefits, (iii) any previously authorized
but unreimbursed business expenses, and (iv)the pro-rata portion of the
Discretionary Bonus set forth in Section 3(c) above which shall be determined
based on the annualization of the Employer's performance criteria in its
then-current fiscal year as established

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through the termination date of this Agreement. If Employee's employment
hereunder terminates because of the death or permanent disability of Employee,
all amounts that may be due to him under this Section 7 shall be paid to him or
his administrators, personal representatives, heirs and legatees, as may be
appropriate.

         If Employee's employment hereunder terminates without cause pursuant
to Section 6(d) above, Employer shall pay to Employee (in addition to the
amounts set forth in Subsections 7(i), 7(ii), 7(iii) and 7(iv) above) salary
payments for the duration of the initial term of this Agreement as set forth in
Section 8 below when and as such salary payments would have come due had the
Employee's employment not been terminated. Any options awarded concurrently
with execution of this Agreement that have not yet vested shall continue to
vest until the end of the initial term of this Agreement set forth in Section 8
below, pursuant to the provisions of Section 4 above. Provided, that in the
event Employee's employment hereunder terminates pursuant to Section 6(d) after
the Employer ceases to conduct business as a going concern as a result of
insolvency or bankruptcy; Employee shall only be entitled to 9 months of
regular salary payments as set forth in Section 3(a) above, accelerated and
payable to Employee immediately upon termination.

         The provisions of Sections 5 and 7 hereof shall survive the
termination of the employment relationship hereunder and this Agreement to the
extent necessary or reasonably appropriate to effect the intent of the parties
hereto as expressed in such provisions.

         8. Term. This Agreement shall be binding and enforceable against
Employer and Employee immediately upon its execution by both such parties. The
stated term of this Agreement and the employment relationship created hereunder
shall begin on June 3, 1998, and shall remain in effect for three years
thereafter, unless sooner terminated in accordance with Section 6 hereof. This
Agreement shall be deemed to be renewed for a month-to-month, at-will basis
after its initial term unless the parties execute an express written renewal
agreement which specifies a different term.

         9. Remedies. Each of the parties to this Agreement will be entitled to
enforce its rights under this Agreement specifically, to recover damages by
reason of any breach of any provision of this Agreement and to exercise all
other rights existing in its favor. Notwithstanding Section 10 below, the
parties hereto agree and acknowledge that money damages may not be an adequate
remedy for any breach of the provisions of this Agreement and that any party
may in its sole discretion apply to any court of law or equity of competent
jurisdiction for specific performance and/or injunctive relief in order to
enforce or prevent any violations of the provisions of this Agreement.

         10. Arbitration. Any controversy or claim arising out of or relating
to this Agreement or relating to Employee's rights, compensation and
responsibilities as an employee shall be determined by binding arbitration in
Dallas, Texas in accordance with the rules of the American Arbitration
Association then in effect. The binding arbitration shall be submitted to a
single arbitrator selected in accordance with the American Arbitration
Association's procedures then in effect for the selection of commercial
arbitrators. This Section 10 shall survive termination of this Agreement for
any reason.

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         11. Assignment. This Agreement is personal to Employee and may not be
assigned in any way by Employee without the prior written consent of Employer.
This Agreement shall not be assignable or delegable by Employer, other than to
an affiliate of Employer; provided, however, that in the event of the merger or
consolidation of Employer the obligations of Employer hereunder shall be
binding upon the surviving or resulting entity of such merger of consolidation.
The rights and obligations under this Agreement shall inure to the benefit of
and shall be binding upon the heirs, legatees, administrators and personal
representatives of Employee and upon the successors, representatives and
assigns of Employer.

         12. Severability and Reformation. The parties hereto intend all
provisions of this Agreement to be enforced to the fullest extent permitted by
law. If, however, any provision of this Agreement is held to be illegal,
invalid, or unenforceable under present or future law, such provision shall be
fully severable, and this Agreement shall be construed and enforced as if such
illegal, invalid, or unenforceable provision were never a part hereof, and the
remaining provisions shall remain in full force and effect and shall not be
affected by the illegal, invalid, or unenforceable provision or by its
severance.

         13. Duty of Good Faith and Fair Dealing. Employer and Employee agree
to deal fairly and in good faith with each other and with respect to all
obligations imposed by this Agreement.

         14. Notices. All notices and other communications required or
permitted to be given hereunder shall be in writing and shall be deemed to have
been duly given if delivered personally, mailed by certified mail (return
receipt requested) or sent by overnight delivery service, cable, telegram,
facsimile transmission or telex to the parties at the following addresses or at
such other addresses as shall be specified by the parties by like notice:



         (a) If to Employer:    Wesley E. Schlenker
                                General Counsel
                                HighwayMaster Corporation
                                16479 Dallas Parkway, Suite 710
                                Dallas, Texas 75248-2621

             If to Employee:    William H. McCausland
                                5901 Castlebar Lane
                                Plano, TX  75093

         Notice so given shall, in the case of notice so given by mail, be
deemed to be given and received on the fourth calendar day after posting, in
the case of notice so given by overnight delivery service, on the date of
actual delivery and, in the case of notice so given by cable, telegram,
facsimile transmission, telex or personal delivery, on the date of actual
transmission or, as the case may be, personal delivery.

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         15. Further Actions. Whether or not specifically required under the
terms of this Agreement, each party hereto shall execute and deliver such
documents and take such further actions as shall be necessary in order for such
party to perform all of his or its obligations specified herein or reasonably
implied from the terms hereof.

         16. GOVERNING LAW; VENUE. THIS AGREEMENT SHALL BE DEEMED MADE WHEN
ACCEPTED BY HIGHWAYMASTER AT HIGHWAYMASTER'S EXECUTIVE OFFICE IN DALLAS, AND
SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE SUBSTANTIVE LAWS OF
THE STATE OF SUCH OFFICE AND EMPLOYEE CONSENTS TO EXCLUSIVE JURISDICTION AND
VENUE AT THE SITE OF SUCH OFFICE, AND TO SERVICE OF PROCESS BY CERTIFIED OR
REGISTERED MAIL. EMPLOYEE ACKNOWLEDGES THAT HIS CONTACTS WITH THE STATE OF
TEXAS ARE SUBSTANTIAL AND CONTINUING, INCLUDING VISITS TO DALLAS FOR TRAINING,
VARIOUS ADMINISTRATIVE FUNCTIONS, ETC.

         17. Entire Agreement and Amendment. This Agreement contains the entire
understanding and agreement between the parties, and supersedes any other
agreement between Employee and Employer, whether oral or in writing, with
respect to the subject matter hereof. This Agreement may not be altered,
amended, or rescinded, nor may any of its provisions be waived, except by an
instrument in writing signed by both parties hereto or, in the case of an
asserted waiver, by the party against whom the waiver is sought to be enforced.

         18. Counterparts. This Agreement may be executed in counterparts, with
the same effect as if both parties had signed the same document. All such
counterparts shall be deemed an original, shall be construed together and shall
constitute one and the same instrument.

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

                                       EMPLOYER:

                                       HIGHWAYMASTER CORPORATION


                                       By: /s/ JANA AHLFINGER BELL
                                           -------------------------------------
                                           JANA AHLFINGER BELL,
                                           President and Chief Executive Officer

                                       EMPLOYEE:


                                       /s/ WILLIAM H. MCCAUSLAND       12/22/98
                                       -----------------------------------------
                                       William H. McCausland