Document:

<PAGE>   1
                                                                  EXHIBIT 10.34b

                                WAIVER UNDER THE
                              TERM CREDIT AGREEMENT

     WAIVER dated as of May 21, 1999 under the $100,000,000 Term Credit
Agreement dated as of March 31, 1998 (as heretofore amended, the "TERM CREDIT
AGREEMENT") among 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, in exchange for up to 8,620,000 shares of the Borrower's common
stock, the Borrower desires to acquire 25 shares of common stock of AMRC
Holdings and certain other securities issued by AMRC Holdings from a trust (the
"TRUST") for the benefit of the shareholders of WorldSpace, Inc. (the
"EXCHANGE");

     WHEREAS, promptly after the Exchange, each share of Common Stock of AMRC
Holdings held by the Borrower will be exchanged for one share of Class B Common
Stock of AMRC Holdings;

     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.

     Section 2.  Waiver. The undersigned Banks hereby waive the failure by the
Borrower to comply with Section 5.13 of the Term Credit Agreement in connection
with the Exchange.

     Section 3.  Exchange of Common Stock. The undersigned Banks and Shareholder
Guarantors (including Hughes in its capacity as agent for the Shareholder
Guarantors) hereby instruct the Collateral Agent to release the shares of Common
Stock of AMRC Holdings held by it pursuant to the Security and Pledge Agreement

<PAGE>   2
and the Shareholder Guarantor Security Agreement upon receipt of an equal number
of shares of Class B Common Stock of AMRC Holdings, together with stock powers
executed in blank.

     Section 4.  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.

     Section 5.  Governing Law. This Waiver shall be governed by and construed
in accordance with the laws of the State of New York.

     Section 6.  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 7.  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 Required 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 8.  Shareholder Guarantor Consent. The Shareholder Guarantors
consent to the foregoing.

                                       2

<PAGE>   3
     IN WITNESS WHEREOF, the parties hereto have caused this Waiver to be duly
executed as of the date first above written.

                                             AMERICAN MOBILE SATELLITE
                                              CORPORATION

                                             By     /s/ Richard J. Burnheimer
                                             -----------------------------------
                                             Title: V.P. and Treasurer

                                             TORONTO DOMINION (TEXAS), INC., as
                                              Administrative Agent and Bank

                                             By     /s/ Jano Mott
                                             -----------------------------------
                                             Title: Vice President

                                             MORGAN GUARANTY TRUST
                                              COMPANY OF NEW YORK

                                             By     /s/ Robert Bottamed
                                             -----------------------------------
                                             Title: Vice President

                                             BANK OF AMERICA NATIONAL TRUST
                                              AND SAVINGS ASSOCIATION

                                             By     /s/ Diane P. Allen
                                             -----------------------------------
                                             Title: Vice President

<PAGE>   4
                                             BANCA COMMERCIALE ITALIANA LOS
                                              ANGELES FOREIGN BRANCH

                                             By     /s/ J. Wityak
                                             ---------------------------------
                                             Title: Vice President

                                             BANCA DI ROMA-SAN FRANCISCO

                                             By
                                             ---------------------------------
                                             Title:

                                             By
                                             ---------------------------------
                                             Title:

                                             THE CHASE MANHATTAN BANK

                                             By
                                             ---------------------------------
                                             Title:

                                             CITIBANK, N.A.

                                             By
                                             ---------------------------------
                                             Title:

<PAGE>   5
                                             DEUTSCHE BANK AG, NEW YORK
                                              BRANCH AND/OR CAYMAN ISLANDS
                                              BRANCH

                                             By     /s/ Joel Makowsky
                                             -----------------------------------
                                             Title: Vice President

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

                                             THE FIRST NATIONAL BANK OF
                                              CHICAGO

                                             By     /s/ Kandis A. Jaffrey
                                             -----------------------------------
                                             Title: Assistant Vice President

                                             ISTITUTO BANCARIO SAN PAOLO DI
                                              TORINO ISTITUTO MOBILIARE
                                              ITALIANO S.P.A.

                                             By
                                             -----------------------------------
                                             Title:

                                             By
                                             -----------------------------------
                                             Title:

                                             NATIONSBANK, N.A.

                                             By     /s/ Diane P. Allen
                                             -----------------------------------
                                             Title: Vice President

<PAGE>   6
                                             HUGHES ELECTRONICS CORPORATION,
                                              as Guarantor and agent for the
                                              Shareholder Guarantors

                                             By     /s/ Mark A. McEachen
                                             -----------------------------------
                                             Title: Corporate V.P. and Treasurer

                                             SINGAPORE TELECOMMUNICATIONS
                                              LTD.

                                             By     /s/ Hoh Wing Chee
                                             -----------------------------------
                                             Title: V.P. (International Network)

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

                                             By     /s/ Morty Schaja
                                             -----------------------------------
                                             Title: Senior Vice President and
                                                    Chief Operating Officer<PAGE>   1
                                                                  EXHIBIT 10.34c

                                                                  CONFORMED COPY

                                 AMENDMENT NO. 2
                                  AND WAIVER OF
                             TERM CREDIT AGREEMENT
                   AND AMENDMENT NO. 1 OF TERM LOAN SECURITY
                              AND PLEDGE AGREEMENT

     AMENDMENT AND WAIVER dated as of November 15, 1999 of the $100,000,000 Term
Credit Agreement dated as of March 31, 1998 (as heretofore amended, the "TERM
CREDIT AGREEMENT") among 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"), and
AMENDMENT dated as of November 15, 1999 of the Term Loan Security and Pledge
Agreement dated as of March 31, 1998 (the "TERM SECURITY AGREEMENT") between the
Borrower and the Administrative Agent (such Amendment and Waiver and such
Amendment, collectively, the "AMENDMENT").

     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 or
the Term Security Agreement has the meaning assigned to such term in the Term
Credit Agreement or the Term Security Agreement. Each reference to "hereof",
"hereunder", "herein" and "hereby" and each other similar reference and each
reference to "this Agreement" and each other similar reference contained in the
Term Credit Agreement or the Term Security Agreement shall, after this Amendment
becomes effective, refer to the Term Credit Agreement or the Term Security
Agreement as amended hereby.

     SECTION 2. Mandatory Prepayments. Section 2.04(b)(i) of the Term Credit
Agreement is amended by adding the following immediately before the expression
"; and":

     , provided that with respect to Reduction Events described in clause (ii)
     of the definition thereof, if the prepayment that would otherwise be
     required to be prepaid in respect of any such Reduction Event is less than
     or exceeds an
<PAGE>   2
     integral multiple of $1,000,000, the prepayment in respect of such lesser
     amount or such excess shall be deferred until the aggregate amount of
     deferred prepayments equals or exceeds $1,000,000

     SECTION 3. Exceptions to Requirement to Preserve Corporate Existence.
Section 5.04 of the Term Credit Agreement is amended by inserting prior to the
colon in the second line thereof the parenthetical phrase "(except as otherwise
permitted pursuant to Section 5.18(j) or (k)".

     SECTION 4. Waiver of Section 2.04(b)(i) of the Term Credit Agreement. The
Banks hereby waive compliance with Section 2.04(b)(i) of the Term Credit
Agreement as in effect prior to the Amendment Effective Date, so long as the
Borrower has at all times been in compliance with Section 2.04(b)(i) of the Term
Credit Agreement as in effect on the Amendment Effective Date.

     SECTION 5. Amendment of Term Security Agreement. Section 13(a) of the Term
Security Agreement is amended to add the following at the end thereof:

     In addition, upon the liquidation, merger, consolidation, combination or
     transfer of all of the assets of any Subsidiary permitted pursuant to
     Section 5.18(j) or (k) of the Credit Agreement with the result that such
     Subsidiary ceases to exist, the security interest in the capital stock of
     such Subsidiary shall automatically terminate, and all rights thereto shall
     revert to such Person as may legally be entitled thereto.

     SECTION 6. Representations of Borrower. The Borrower represents and
warrants that, after giving effect to this Amendment, (i) the representations
and warranties set forth in Article 4 of the Term Credit Agreement shall be true
on and as of the Amendment Effective Date and (ii) no Default shall have
occurred and be continuing on such date.

     SECTION 7. Governing Law. This Amendment shall be governed by and construed
in accordance with the laws of the State of New York.

     SECTION 8. Counterparts. This Amendment 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 9. Effectiveness. This Amendment shall become effective as of the
date hereof on the date (the "AMENDMENT EFFECTIVE DATE") when the Documentation
Agent shall have received a counterpart hereof from each of the Borrower,
Hughes,

                                        2
<PAGE>   3
SingTel, Baron Capital, the Administrative Agent and the Required 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 10. Shareholder Guarantor Consent. The Shareholder Guarantors
consent to the foregoing.

                                        3
<PAGE>   4
     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the date first above written.

                                         AMERICAN MOBILE SATELLITE
                                          CORPORATION

                                         By: /s/ RICHARD J. BURNHEIMER
                                         ---------------------------------------
                                         Title: Vice President and Treasurer

                                         TORONTO DOMINION (TEXAS), INC., as
                                          Administrative Agent and Bank

                                         By: /s/ WARREN FINLAY
                                         ---------------------------------------
                                         Title: President

                                         MORGAN GUARANTY TRUST COMPANY
                                          OF NEW YORK

                                         By: /s/ ROBERT BOTTAMEDI
                                         ---------------------------------------
                                         Title: Vice President

                                         BANK OF AMERICA, N.A.

                                         By:
                                         ---------------------------------------
                                         Title:
<PAGE>   5
                                          BANCA COMMERCIALE ITALIANA LOS
                                           ANGELES FOREIGN BRANCH

                                          By: /s/ C. DOUGHERTY
                                          --------------------------------------
                                          Title: Vice President

                                          By: /s/ E. BERMANT
                                          --------------------------------------
                                          Title: FVP/Deputy Manager

                                          BANCA DI ROMA-SAN FRANCISCO

                                          By: /s/ ERIC MAUBERT
                                          --------------------------------------
                                          Title: Assistant Vice President

                                          By: /s/ FRANCESCO BAROLO
                                          --------------------------------------
                                          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>   6
                                            DEUTSCHE BANK AG, NEW YORK
                                             BRANCH AND/OR CAYMAN ISLANDS
                                             BRANCH

                                            By: /s/ JOEL MAKOWSKY
                                            ------------------------------------
                                            Title: Vice President

                                            By: /s/ ANDREAS NEUMEIER
                                            ------------------------------------
                                            Title: Vice President

                                            BANK ONE, N.A.

                                            By: /s/ STEPHANIE A. MACK
                                            ------------------------------------
                                            Title: Commercial Banking Officer

                                            SANPAOLO IMI S.P.A.

                                            By:
                                            ------------------------------------
                                            Title:

                                            By:
                                            ------------------------------------
                                            Title:
<PAGE>   7
Consented to by:

HUGHES ELECTRONICS CORPORATION,
 as Guarantor and agent for the
 Shareholder Guarantors

By: /s/ MARK A. McEACHEN
------------------------------------
Title: Corporate Vice President
       & Treasurer

SINGAPORE TELECOMMUNICATIONS LTD.

By: /s/ HOH WING CHEE
------------------------------------
Title: Vice President

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

By: /s/ MORTY SCHAJA
------------------------------------
Title: Senior Vice President & COO

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