EXHIBIT 10.30d

                                 AMENDMENT NO. 4
              TO WARRANT CERTIFICATES FOR THE PURCHASE OF SHARES OF
                       COMMON STOCK OF MOTIENT CORPORATION

     AMENDMENT  dated as of June 29, 2000 to each of those Warrant  Certificates
dated as of June 28, 1996 (as amended, the "Warrants" and capitalized terms used
herein and not otherwise defined shall have the meanings ascribed thereto in the
Warrants),  issued by Motient  Corporation  (formerly  American Mobile Satellite
Corporation) (the "Company") to each of Hughes Electronics Corporation and Baron
Capital Partners, L.P. (collectively, the "Holders").

                              W I T N E S S E T H:

     WHEREAS,  the  Company  previously  issued  to the  Holders  Warrants  that
represented  in the aggregate the right to purchase  4,905,974  shares of Common
Stock at an Exercise Price of $7.3571 per share;

     WHEREAS,  the  Company,  the  Holders,  Singapore  Telecommunications  Ltd.
("SingTel"),  Motient Holdings Inc. (formerly AMSC Acquisition  Company,  Inc.),
the  Banks  party  thereto,  Morgan  Guaranty  Trust  Company  of New  York,  as
Documentation  Agent  ("Morgan"),   and  Toronto  Dominion  (Texas),   Inc.,  as
Administrative  Agent ("Toronto Dominion") have entered into that certain Waiver
dated as of June 29, 2000 under the Revolving Credit Agreement dated as of March
31, 1998 (the  "Revolver  Waiver") and the Company,  the Holders,  SingTel,  the
Banks party thereto,  Morgan and Toronto Dominion have entered into that certain
Waiver  dated as of June 29,  2000 under the Term Credit  Agreement  dated as of
March 31, 1998 (the "Term  Waiver";  the  Revolver  Waiver and the Term  Waiver,
collectively, the "Waivers"); and

     WHEREAS,  in  connection  with the Holders'  execution of the Waivers,  the
parties hereto desire to amend certain terms of the Warrants.

     NOW, THEREFORE, the undersigned parties hereto agree as follows:

     SECTION 1.  Amendment.  Section 1 of each of the Warrants is hereby amended
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by  modifying  the  definition  of  "Exercise  Price" to read in its entirety as
follows:

     "Exercise  Price" means initially $6.25 per Warrant Share, as adjusted from
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time to time.

     SECTION 2.  Effectiveness.  This Amendment shall become effective as of the
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first date of which each of the parties hereto shall have executed a counterpart
hereof and each of the Satellite  Business  Transactions  (as defined in each of
the Waivers) shall have been consummated.

     SECTION 3.  Reaffirmance.  Except as expressly amended hereby, the terms of
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the Warrants  remain  unchanged and the Warrants,  as previously  amended and as
amended hereby, are in full force and effect.

     SECTION 4. Issuance of Replacement Warrant. Upon the request of any Holder,
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the Company  promptly  shall issue a new Warrant,  incorporating  the amendments
effected hereby and all previous amendments to replace the presently outstanding
Warrant held by such Holder.





     IN WITNESS WHEREOF,  each of the parties hereto has executed this Amendment
No. 4 by its duly  authorized  officer  as of the day and year  first  set forth
above.

                                MOTIENT CORPORATION
                                (formerly American Mobile Satellite Corporation)

                                By:     /s/Randy Segal
                                Name    Randy Segal
                                Title:  SVP

                                HUGHES ELECTRONICS CORPORATION

                                By:     /s/Mark McEachen
                                Name    Mark McEachen
                                Title:  Corporate Vice President & Treasurer

                                BARON CAPITAL PARTNERS, L.P.,
                                a Delaware limited partnership

                                By:  Baron Capital Management, Inc.,
                                a General Partner

                                By:     /s/Linda S. Martinson
                                Name    Linda S. Martinson
                                Title:  VP-General Counsel