Document:

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
                 ---------
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
      ---------------
time to time.

     SECTION 2.  Effectiveness.  This Amendment shall become effective as of the
                 -------------
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
                 ------------
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,
                -------------------------------
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.

<PAGE>

     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 CounselEXHIBIT 10.32b

                                 AMENDMENT NO. 2
              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 March 31, 1998 (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  891,995  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 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
      ---------------
time to time.

     SECTION 2.  Effectiveness.  This Amendment shall become effective as of the
                 -------------
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
                 ------------
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,
                -------------------------------
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.

<PAGE>

     IN WITNESS WHEREOF,  each of the parties hereto has executed this Amendment
No. 2 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: V.P. & General CounselEXHIBIT 10.34d

                                WAIVER UNDER THE
                              TERM CREDIT AGREEMENT

     WAIVER dated as of June 27, 2000 under the Term Credit  Agreement  dated as
of March 31, 1998 (as heretofore  amended,  the "Term Credit  Agreement")  among
MOTIENT  CORPORATION  (formerly  AMERICAN  MOBILE  SATELLITE  CORPORATION)  (the
"Borrower"),  the BANKS party  thereto  (the  "Banks"),  MORGAN  GUARANTY  TRUST
COMPANY OF NEW YORK, as Documentation  Agent (the  "Documentation  Agent"),  and
TORONTO DOMINION  (TEXAS),  INC., as Administrative  Agent (the  "Administrative
Agent").

                              W I T N E S S E T H :

     WHEREAS,  the  Borrower  proposes  to  enter  into the  Satellite  Business
Transactions (as defined below);

     WHEREAS,  the undersigned Banks and the Shareholder  Guarantors are willing
to consent to the foregoing  and to waive certain  provisions of the Term Credit
Agreement in connection with the foregoing;

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

     SECTION 1. Definitions;  References.  Unless otherwise specifically defined
herein,  each term used herein which is defined in the Term Credit Agreement has
the meaning assigned to such term in the Term Credit Agreement. In addition:

     "Satellite Business  Transactions" means the following  transactions , each
as more fully  described  in the  Investment  Agreement,  Asset Sale  Agreement,
Research  &  Development,   Marketing  and  Service  Agreement,  LLC  Agreement,
Registration  Rights  Agreement,  Cross-Licensing  and Bulk Resale Agreement and
Parent Transfer Letter Agreement  (collectively,  the "Transaction  Documents"),
each  substantially  in the form delivered to each of the Banks and  Shareholder
Guarantors  prior to June 24, 2000:  (i) the  formation by the Borrower of a new
directly-owned  Subsidiary,  Motient  Satellite  Ventures,  LLC  ("Newco"),  the
Borrower's  interest in which may  subsequently  be  transferred  to another new
directly-owned  Subsidiary of the Borrower; (ii) the issuance by Newco to Telcom
Ventures,  L.L.C., Columbia Capital Corporation and Spectrum Equity Investors LP

<PAGE>

or designated  subsidiaries  or affiliates  thereof (each,  a  "Purchaser",  and
collectively,  the  "Purchasers"),  in  consideration  of  the  payment  by  the
Purchasers  to  Newco  of   $50,000,000,   of  membership   interests  of  Newco
constituting  20% of the fully  diluted  membership  interests of Newco  ("Newco
Purchaser  Interests") which, at the option of each Purchaser,  may be exchanged
for common shares of the Borrower; (iii) the issuance by Newco to the Purchasers
of an option (the "Newco Option"),  which may be exercised by one or more of the
Purchasers,  to  purchase  an  additional  40% of the fully  diluted  membership
interests of Newco (plus, if fewer than all of the Purchasers exercise the Newco
Option, such additional interests (the "Additional  Interests") as are necessary
to result in such  Purchasers  collectively  owning  50.1% of the fully  diluted
membership interests of Newco),  exercisable for $120,000,000 for the first year
of the option,  increasing  by  $3,600,000  per full  calendar  month during the
second and final year of the  option,  plus an amount to reflect the sale of any
Additional  Interests  at the same  price  per unit  that is paid for the 40% of
Newco's  membership  interests  (the "Newco Option  Exercise  Price");  (iv) the
exercise of the Newco Option,  as a result of which the Borrower  shall own less
than half of the fully  diluted  membership  interests  of Newco and Newco shall
cease to be a Subsidiary of the Borrower or a member of the Borrower Group;  (v)
the  execution by Newco and Motient  Services  Inc.  (formerly  AMSC  Subsidiary
Corporation) ("Motient Services"),  a direct wholly-owned  subsidiary of Motient
Holdings Inc.  (formerly  AMSC  Acquisition  Company,  Inc.),  of a research and
development and marketing and service  agreement (the "R&D Agreement")  relating
to Motient Services'  satellite  communications  services business,  pursuant to
which  Newco  shall  pay to  Motient  Services  $20,000,000  of the  $50,000,000
received  from the  Purchasers  in exchange for access to such  business and the
right to develop new  business  opportunities  therefor;  (vi) the  execution by
Newco and Motient Services of an asset sale agreement  pursuant to which, for an
initial payment to Motient  Services of $24,000,000 of the $50,000,000  received
from the Purchasers and an additional  payment to Motient  Services equal to the
Newco  Option  Exercise  Price,  Newco shall have the right to purchase  Motient
Services'  satellite  communications  services  business  (either  directly from
Motient Services or by purchasing the equity of a new, directly-owned Subsidiary
of Motient Services to which such business shall have been  contributed);  (vii)
the formation by the Borrower of one or more other directly-owned  Subsidiaries,
if necessary  solely to effect an exchange by the Purchasers of Newco  Purchaser
Interests for common shares of the Borrower (whether through a triangular merger
of Newco, such Subsidiaries and the Borrower or otherwise) and the merger of one
or  more  such  Subsidiaries  with  one or  more  of  the  Purchasers  or  their
transferees;   (viii)  the  performance  by  Newco,  Motient  Services,  Motient
Communications  Company and the Borrower of their respective  obligations  under
the Transaction Documents (including,  without limitation,  obligations relating
to indemnification,  the sharing and cross- licensing of assets, the disposition

<PAGE>

by the Borrower  (directly or through a transaction  involving a Subsidiary)  of
its remaining membership interests in Newco in a "drag-along"  transaction,  and
the  payment  by  Motient  Services  to  Newco  of  $44,000,000   under  certain
circumstances and subject to certain conditions  relating to the sale by Motient
Services of its satellite  business to a third party, the failure of a satellite
or the loss of certain FCC  licenses);  and (ix) the  conversion of Newco from a
limited  liability  company to a  corporation,  or the  liquidation  of Newco in
accordance with the terms of the LLC Agreement.

     SECTION  2.  Waiver.  The  undersigned  Banks  waive  compliance  with  the
provisions  of  Article  5 of the  Term  Credit  Agreement  (including,  without
limitation,  Sections 5.04,  5.13, 5.17, 5.18, 5.20 and 5.21) to the extent (and
only to the extent)  necessary to permit the  Satellite  Business  Transactions.
Subject to the next sentence,  the undersigned  Banks agree that each of (i) the
purchase  by the  Purchasers  of the  Newco  Purchaser  Interests  and  (ii) the
exercise by one or more  Purchasers  of the Newco  Option (and none of the other
Satellite  Business  Transactions,  with the exception of any other  transfer or
disposition  by the  Borrower  of any  portion of its  interest  in Newco or any
successor  to Newco,  to the extent such  transfer or  disposition  is or may be
contemplated  by  the  Satellite  Business   Transactions)  shall  constitute  a
Reduction Event requiring a prepayment of Loans under Section  2.04(b)(i) to the
extent of any applicable  Net Cash  Proceeds,  with respect to which (x) the Net
Cash  Proceeds  shall be  $44,000,000  in the case of the  purchase of the Newco
Purchaser  Interests (the "Newco Purchaser  Interests  Reduction  Event") and an
amount equal to the Newco Option  Exercise  Price in the case of the exercise of
the Newco Option,  in each case less any portion thereof to which the "Reduction
Percentage"  (as defined in the  Revolving  Credit  Agreement) is applied to the
reduction of the "Commitments"  (as defined in the Revolving Credit  Agreement),
and (y) the Reduction  Percentage  shall be 50%. The undersigned  Banks agree to
waive the  requirement  that Tranche A Loans and Tranche C Loans be prepaid upon
the occurrence of the Newco Purchaser  Interests  Reduction  Event; as a result,
only the Tranche B Loans are subject to reduction  upon such  occurrence,  in an
amount  equal to 12.5% of the net  amount  (if any)  which  would  otherwise  be
available to prepay all the Loans.  To the extent that the membership  interests
transferred to one or more  Purchasers upon the exercise of the Newco Option are
existing  membership  interests of Newco held by the Borrower,  the  undersigned
Banks authorize the Administrative Agent to release the Liens on such membership
interests created by the Security and Pledge Agreement.

     SECTION  3.  Representations  of  Borrower.  The  Borrower  represents  and
warrants that (i) the  representations  and warranties set forth in Article 4 of
the Term Credit Agreement shall be true on and as of the Effective Date and (ii)
no Default shall have occurred and be continuing on such date.

<PAGE>

     SECTION 4. Governing Law. This Waiver shall be governed by and construed in
accordance with the laws of the State of New York.

     SECTION  5.  Counterparts.  This  Waiver  may be  signed  in any  number of
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

     SECTION 6. Effectiveness. This Waiver shall become effective as of the date
hereof on the date (the  "Effective  Date") when the  Documentation  Agent shall
have received a counterpart hereof from each of the Borrower,  Hughes,  SingTel,
Baron Capital and the Banks signed by such party or a facsimile or other written
confirmation (in form satisfactory to the  Documentation  Agent) that such party
has signed a counterpart hereof.

     SECTION  7.  Shareholder  Guarantor  Consent.  The  Shareholder  Guarantors
consent  to the  foregoing,  and  authorize  Hughes  to  release  the  Liens  on
membership  interests of Newco  created by the  Shareholder  Guarantor  Security
Agreement  under the  circumstances  described in the last sentence of Section 2
above.

<PAGE>

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

                             MOTIENT CORPORATION
                             (formerly AMERICAN MOBILE SATELLITE CORPORATION)

                             By:  /s/ Randy Segal
                             Title: Senior Vice President

                             TORONTO DOMINION (TEXAS), INC.

                             By:  /s/ Jeffrey R. Lents
                             Title: Vice President

                             MORGAN GUARANTY TRUST COMPANY OF NEW YORK

                             By:  /s/ Robert Bottamedi
                             Title: Vice President

                             BANK OF AMERICA, N.A.

                             By:  /s/ Dianne J. Prust
                             Title:  Principal

<PAGE>

                             BANCA COMMERCIALE ITALIANA LOS
                             ANGELES FOREIGN BRANCH

                             By:  /s/ Charles Dougherty
                             Title: Vice President

                             By:  s/ Frank Maffei
                             Title: Authorized Signature

                             BANCA DI ROMA - SAN FRANCISCO

                             By: /s/ Richard G. Dietz
                             Title: Vice President

                             By: /s/ Luca Balestra
                             Title: Senior Vice President & Manager

                             THE CHASE MANHATTAN BANK

                             By: /s/ Tracey Navin Ewing
                             Title: Vice President

                             CITICORP USA, INC.

                             By:  /s/ Walter L. Larsen
                             Title:  Managing Director

<PAGE>

                             DEUTSCHE BANK AG, NEW YORK
                             BRANCH AND/OR CAYMAN ISLANDS
                             BRANCH

                             By:  /s/ Virginia Mahler Cosenza
                             Title: Vice President

                             By:  /s/ Robert B. Landis
                             Title: Managing Director

                             BANK ONE, N.A.

                             By:  /s/ Stephanie A. Mack
                             Title:  Commercial Banking Officer

                             SAN PAOLO IMI S.P.A.

                             By:  /s/ Carlo Persico
                             Title: Deputy General Manager

                             By:  /s/ Robert Wurster
                             Title: 1st Vice President

                             HUGHES ELECTRONICS CORPORATION

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

<PAGE>

                             SINGAPORE TELECOMMUNICATIONS LTD.

                             By:  /s/ Hoh Wing Chee
                             Title: Vice President
                                    International Network

                             BARON CAPITAL PARTNERS, L.P., a
                             Delaware limited partnership
                             By: BARON CAPITAL MANAGEMENT,
                                 INC., a general partner

                             By:    /s/ Linda S. Martinson
                             Title: Vice President & General Counsel

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