<PAGE>   1
                                                                   Exhibit 10.30

                                                                  4 YEAR VESTING


                       HIGHWAYMASTER COMMUNICATIONS, INC.

                             STOCK OPTION AGREEMENT

         This OPTION AGREEMENT is entered into by and between HighwayMaster
Communications, Inc., a Delaware corporation (the "Company"), and the
undersigned employee of the Company's subsidiary, HighwayMaster Corporation,
(the "Optionee").

         1.      Grant of Option.  The Company hereby grants to the Optionee
effective as of the date set forth in Section 18 hereof (the "Date of Grant"),
the right and option (the "Option") to purchase up to the aggregate number of
shares of common stock, par value $.01 per share, of the Company (the "Common
Stock") set forth in Section 18 hereof, subject to adjustment pursuant to
Section 3 hereof and subject to the Optionee's acceptance and agreement to all
of the terms and conditions and restrictions described in the HighwayMaster
Communications, Inc. (formerly known as HM Holding Corporation) 1994 Stock
Option Plan, as amended (the "Plan"), a copy of which has been provided to the
Optionee, and to the further terms, conditions and restrictions set forth
below.

         2.      Exercise Price.  Subject to adjustment pursuant to Section 3,
the exercise price payable by the Optionee upon exercise of this Option is set
forth in Section 18 hereof.

         3.      Adjustments to Number of Shares and Option Price.  The number
of shares of Common Stock exercisable under this Option and exercise price have
been adjusted to give effect to the purchase under that certain Subscription
Agreement dated February 4, 1994, by and among the Company and the Purchasers
listed therein by such Purchasers of an aggregate of 2,130.435 shares of Common
Stock of the Company.  The number of shares and exercise price shall also be
adjusted as provided in Section 9.3 of the Plan.
<PAGE>   2
         4.      Tax Status.  This Option will be treated as an "incentive
stock option" within the meaning of Section 422 of the Code to the extent that
any portion of this Option meets the requirements of Section 422 of the Code.
To the extent that any portion of this Option does not meet such Code
requirements, this Option shall be deemed a nonqualified stock option.

         5.      Exercise of Option.  Subject to the terms of the Plan and this
Option Agreement, as of the Date of Grant and each of the first, second, third
and fourth anniversaries of the Date of Grant, Optionee may exercise
(cumulatively) rights to acquire one-fifth of the Common Stock subject to the
Option.

         6.      Expiration of Option.  This Option shall expire and cease to
be exercisable on the sixth anniversary of the Date of Grant or such earlier
date as may be specified in the Plan.

         7.      Termination of Affiliation.

                 (a)      Subject to the following provisions of this Section 7
         and Article VI of the Plan, this Option may not be exercised unless at
         the time of exercise the Optionee is an Employee of the Company or a
         Subsidiary.

                 (b)      If the Optionee's position as an Employee of the
         Company or a Subsidiary shall terminate for any reason other than
         death, the Optionee may exercise this Option, to the same extent it
         was exercisable on the date of such termination, during the 60-day
         period following the date of such termination.  In no event may the
         Optionee exercise this Option later than the date on which the Option
         would have expired under Section 6 hereof.

                 (c)      If the Optionee's position as an Employee of the
         Company or a Subsidiary shall terminate by reason of the Optionee's
         death, the executor or administrator of the Optionee's estate or the
         person to whom this Option is transferred by will or the laws of
         descent or


                                      2
<PAGE>   3
         distribution may exercise this Option with respect to any or all
         shares covered by this Option within 60 days after the date of the
         Optionee's death.

         8.      Procedure to Exercise.  This Option may be exercised only by
delivery of a written notice to the Company at its principal office, stating
the number of shares of Common Stock as to which the Option is being exercised
and accompanied by payment in full in cash or by certified check of the
exercise price for all such shares.

         9.      Nontransferability of Option.  This Option shall not be
assignable or transferable other than by will or the laws of descent and
distribution and shall be exercisable only by the Optionee during his lifetime.

         10.     Continued Employment or Retention.  Subject to the terms of
any employment agreement between the Company and the Optionee, nothing herein
shall confer upon the Optionee any right to be continued in the employ or
retention of the Company or a Subsidiary or shall prevent the Company or
Subsidiary which employs or retains the Optionee from terminating such
employment at any time, with or without cause.

         11.     Rights as Shareholder.  Nothing herein is intended to or shall
give to the Optionee any right or status of any kind as a stockholder of the
Company in respect of any shares of Common Stock covered by this Option or
entitle the Optionee to any dividends or distributions thereon unless and until
such shares shall have been delivered to the Optionee and registered in the
Optionee's name.

         12.     Interpretation.  If and when questions arise from time to time
as to the intent, meaning or application of the provisions hereof or of the
Plan, such questions shall be decided by the Board of Directors or the
Committee in its sole discretion, and any such decision shall be conclusive and
binding on the Optionee.  The Optionee hereby agrees that this Option is
granted and accepted subject to such condition and understanding.



                                       3
<PAGE>   4
         13.     Investment Representation.  At such time or times as the
Optionee may exercise this Option, the Optionee shall, upon the request of the
Company, represent in writing (i) that the shares being acquired by the
Optionee will not be sold except pursuant to an effective registration
statement, or applicable exemption from registration, under the Securities Act
of 1933, as amended, (ii) that it is the Optionee's intention to acquire the
shares being acquired for investment only and not with a view to distribution
thereof, and (iii) other customary representations as the Company deems
necessary or advisable.  No shares will be issued unless and until the Company
is satisfied as to the accuracy of such representations.

         14.     Withholding of Taxes.  Upon exercise of this Option (either
wholly or in part), the Optionee must pay to the Company, or make arrangements
satisfactory to the Company regarding payment of, any federal, state or local
taxes of any kind required to be withheld in connection with the issuance to
the Optionee of Common Stock upon exercise of this Option.

         15.     Notices.  All notices and other communications hereunder shall
be in writing and shall be deemed to have been duly given if delivered
personally, mailed certified mail (return receipt requested) or sent by
overnight delivery service, cable, telegram, facsimile transmission or telex to
the Optionee at the address on the signature page hereof and to the Company at
the address set forth below or at such other addresses as shall be specified by
the parties by like notice:

                 HighwayMaster Communications, Inc.
                 1155 Kas Drive
                 Richardson, Texas  75081
                 Fax:  (972) 301-2263
                 Attn:  Secretary & General Counsel

         16.     Defined Terms.  All capitalized terms used herein and not
otherwise defined shall have the meanings given them in the Plan.



                                       4
<PAGE>   5
         17.     Confidentiality.  Unless otherwise permitted by the Chairman of
         the Board or the President of the Company, Optionee agrees to keep
         confidential the terms of this Option Agreement (and the terms of any
         other Option Agreement with any other employee of the Company known to
         Optionee) and shall not disclose such terms to any other employee or
         otherwise.

         18.     Specified Information.  This Option Agreement shall apply with
respect to the following specific information:

                 a.   Date of Grant:  SEPTEMBER 18, 1998

                 b.   Name of Optionee: BILL MCCAUSLAND

                 c.   Adjusted Number of Shares Covered by Option: 20,000

                 d.   Option Exercise Price Per Share:  $1.19

IN WITNESS WHEREOF, the undersigned have executed this Option Agreement to be
effective as of the Date of Grant set forth above.

                                         HIGHWAYMASTER COMMUNICATIONS, INC.

                                         By: /s/ JANA BELL
                                             ----------------------------------
                                         Name: Jana Bell
                                               --------------------------------
                                         Title: President and CEO          
                                                -------------------------------


                                           /s/ WILLIAM H. MCCAUSLAND   12/22/98
                                         --------------------------------------
                                         BILL MCCAUSLAND, Optionee



                                       5