AMERICAN MOBILE SATELLITE CORP
PRE 14A, 1999-07-23
COMMUNICATIONS SERVICES, NEC
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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


I.   SCHEDULE 14A INFORMATION

     A. Proxy Statement Pursuant to Section 14(a) of the Securities Exchange
        Act of 1934


Filed by the Registrant |X|
Filed by a Party other than the Registrant |_|

Check the appropriate box:

|X|  Preliminary Proxy Statement
|_|  Confidential,  for  Use  of the  Commission  Only  (as  permitted  by  Rule
     14a-6(e)(2))
| |  Definitive Proxy Statement
|_|  Definitive  Additional Materials
|_|  Soliciting Material Pursuant to ss. 240.14a-11(c) or ss. 240.14a-12


                      American Mobile Satellite Corporation
                (Name of Registrant as Specified in Its Charter)

                                 Randy S. Segal
                   (Name of Person(s) Filing Proxy Statement)


Payment of Filing Fee (Check the appropriate box):

|X| No fee required.

|_| Fee computed on table below per Exchange Act Rules 14a-6(i)(4) and 0-11.

1)   Title of each class of securities to which transaction  applies:
2)   Aggregate number of securities to which transaction applies:
3)   Per unit price or other underlying value of transaction  computed  pursuant
     to Exchange  Act Rule O-11 (Set forth the amount on which the filing fee is
     calculated and state how it was determined):
4)   Proposed maximum aggregate value of transaction:
5)   Total fee paid:


     |_| Fee paid previously with preliminary materials.
     |_| Check box if any part of the fee is offset as provided by Exchange  Act
         Rule  0-11(a)(2)  and identify the filing for which the  offsetting fee
         was paid  previously.  Identify  the  previous  filing by  registration
         statement number, or the Form or Schedule and the date of its filing.

         1)   Amount Previously Paid:
         2)   Form Schedule or Registration Statement No.:
         3)   Filing Party:
         4)   Date Filed:






<PAGE>

[GRAPHIC OMITTED]







American Mobile Satellite Corporation
10802 Parkridge Boulevard
Reston, Virginia  20191-5416
(703) 758-6000



                                 August 6, 1999



Dear Stockholder:

You are  cordially  invited  to  attend a special  meeting  of  stockholders  of
American  Mobile  Satellite  Corporation  to be held at 9:00  a.m.  on  Tuesday,
September  7, 1999 at the  offices  of  American  Mobile  Satellite  Corporation
located at 10802 Parkridge Boulevard, Reston, Virginia 20191.

The formal  notice of special  meeting and proxy  statement are attached to this
letter.  This  material  contains  information  concerning  the  business  to be
conducted at the meeting.

Even if you are unable to attend the  meeting in person,  it is  important  that
your shares be represented.  Therefore,  I urge you to complete,  date, sign and
return the enclosed  proxy card at your earliest  convenience.  If you choose to
attend the annual meeting,  you may, of course,  revoke your proxy and cast your
votes personally at the meeting.

                                                      Sincerely,
                                                      /s/Gary M. Parsons
                                                      Gary M. Parsons
                                                      Chairman of the Board



<PAGE>




[GRAPHIC OMITTED]






American Mobile Satellite Corporation
10802 Parkridge Boulevard
Reston, Virginia  20191-5416


NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

To the Stockholders of American Mobile Satellite Corporation:

A special  meeting of  stockholders  of American  Mobile  Satellite  Corporation
("American  Mobile" or the  "Company")  will be held at the  offices of American
Mobile, 10802 Parkridge Boulevard,  Reston,  Virginia,  on September 7, 1999, at
9:00 a.m. local time, for the following purposes:

1. To consider and act upon a proposal to issue shares of American Mobile Common
Stock to XM Ventures in connection with the Exchange  Agreement  entered into by
the Company with  WorldSpace,  Inc., XM Satellite Radio  Holdings,  Inc., and XM
Ventures;

2. To approve an amendment to the Company's Amended and Restated  Certificate of
Incorporation  to increase the number of shares of Common Stock  authorized  for
issuance from 75,000,000 shares to 150,000,000 shares; and

3. To transact such other business as may be properly brought before the meeting
or any postponements or adjournments thereof.

Only  holders  of  record  of  American  Mobile's  Common  Stock at the close of
business on July 14, 1999,  will be entitled to vote at the  meeting.  A list of
such  stockholders  will  be  available  at the  Company's  headquarters,  10802
Parkridge Boulevard,  Reston,  Virginia,  for examination during normal business
hours by any  stockholder for any purpose germane to the meeting for a period of
ten days prior to the meeting.

Stockholders  who do not  expect to attend  the  meeting  in person are asked to
date,  sign and complete the enclosed  proxy and return it without  delay in the
enclosed envelope, which requires no postage if mailed in the United States.

                                            By order of the Board of Directors,
                                            Randy S. Segal
                                            Senior Vice President and Secretary

Reston, Virginia
August 6, 1999



<PAGE>




[GRAPHIC OMITTED]





American Mobile Satellite Corporation
10802 Parkridge Boulevard
Reston, Virginia  20191-5416
(703) 758-6000

                                PROXY STATEMENT
                                ---------------

The  accompanying  proxy is  solicited  on behalf of the Board of  Directors  of
American Mobile Satellite  Corporation  ("American Mobile" or the "Company") for
use at a special  meeting of  stockholders  to be held on September 7, 1999, and
any  postponement or adjournments  thereof.  The special meeting will be held at
the  principal  executive  offices of the  Company,  which are  located at 10802
Parkridge  Boulevard,  Reston,  Virginia,  and will commence at 9:00 a.m.  local
time.  Any  stockholder  giving a proxy may  revoke it at any time  before it is
exercised at the meeting by  delivering  to the  Secretary of American  Mobile a
written  instrument of revocation or a duly executed proxy bearing a later date.
This proxy statement and the accompanying  form of proxy are being first sent to
stockholders on or about August 6, 1999.

The only class of securities of American  Mobile entitled to vote at the special
meeting is its Common Stock, of which 39,136,801 shares were outstanding on July
14, 1999. Only stockholders of record at the close of business on July 14, 1999,
will be  entitled to vote at the special  meeting.  The  presence at the special
meeting of the  holders of a majority  of the issued and  outstanding  shares of
Common  Stock  entitled  to vote,  either in person or  represented  by properly
executed  proxies,  is necessary to constitute a quorum for the  transaction  of
business at the  meeting.  If there are not  sufficient  shares  represented  in
person or by proxy at the  meeting to  constitute  a quorum,  the meeting may be
postponed or adjourned in order to permit further solicitation of proxies by the
Company.  Proxies given  pursuant to this  solicitation  and not revoked will be
voted at any  postponement  or  adjournment  of the annual meeting in the manner
described  elsewhere in this proxy statement.  Each stockholder has one vote for
each share of Common Stock held.

Proposal 1, which seeks  approval  for the issuance of shares of Common Stock to
XM Ventures,  will require the affirmative vote of a majority of the total votes
cast on  Proposal  1,  without  reference  to the  shares  currently  held by XM
Ventures.  Abstentions  will not  have any  effect  on the vote on  Proposal  1.
Proposal 2, which seeks  approval of an  amendment  to the Amended and  Restated
Certificate of Incorporation, will require the affirmative vote of two-thirds of
the issued and outstanding  shares of Common Stock.  Abstentions with respect to
Proposal 2 will have the same effect as a vote against Proposal 2.


                                        1

<PAGE>



Brokers  who hold  shares in street  name do not have the  authority  to vote on
certain  matters for which they have not received  instructions  from beneficial
owners.  Broker  non-votes  will be counted in  determining  the  existence of a
quorum.  Such broker  non-votes  with  respect to Proposal 1 will not affect the
outcome of the vote on that Proposal.  Broker  non-votes will not be included in
the vote  totals on  Proposal 2, and thus will affect the outcome of the vote on
that Proposal.

The cost of soliciting  proxies in the form  enclosed  herewith will be borne by
the Company.  In addition to the  solicitation  of proxies by mail, the Company,
through its directors,  officers and regular employees, also may solicit proxies
personally or by telephone.  The Company also will request  persons,  firms, and
corporations  holding  Common  Stock  in their  names  or in the  names of their
nominees,  which are beneficially owned by others, to send proxy material to and
obtain  proxies from the  beneficial  owners and will  reimburse the holders for
their reasonable expenses in so doing.

This proxy statement  contains and  incorporates by reference  certain  forward-
looking  statements  within the meaning of Section 27A of the  Securities Act of
1933,  as amended,  and Section 21E of the  Securities  Exchange Act of 1934, as
amended.  We intend such  forward-looking  statements  to be covered by the safe
harbor  provisions  for  forward-looking   statements  in  these  sections.  All
statements  regarding our expected financial position and operating results, our
business strategy, and our financing plans are forward-looking statements. These
statements can sometimes be identified by our use of forward-looking  words such
as "may," "will,"  "anticipate,"  "estimate,"  "expect," "project," or "intend."
These forward-looking  statements reflect our plans,  expectations,  and beliefs
and,  accordingly,  are subject to certain  risks and  uncertainties.  We cannot
guarantee that any of such forward-looking statements will be realized.


                                        2

<PAGE>



               SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND
               ---------------------------------------------------
                                   MANAGEMENT
                                   ----------

  The following table and the accompanying  notes set forth certain  information
concerning the beneficial ownership of the Company's common stock as of June 30,
1999  (except  where  otherwise  indicated),  by each person who is known by the
Company to own  beneficially  more than five percent of its common  stock,  each
director and each executive officer, and all directors and executive officers as
a group.  Except as  otherwise  indicated,  each person  listed in the table has
informed the Company that such person has sole voting and investment  power with
respect  to such  person's  shares of common  stock and  record  and  beneficial
ownership with respect to such person's shares of common stock.

<TABLE>

                                                               Number of
<CAPTION>
         Name of Beneficial Owner(1)                            Shares              % of
                                                                                    Class
Beneficial Owners of More than 5%

<S>                                                           <C>                  <C>
AT&T Wireless Services, Inc.(2).............                   3,001,145            9.22%
  1150 Connecticut Avenue, N.W.
  Washington, DC 20036
Singapore Telecommunications Limited (3)....                   4,836,746           14.49%
  31 Exeter Road, Comcentre
  Singapore 239732
  Republic of Singapore
Motorola, Inc.(4)...........................                   6,520,532           20.03%
  1303 East Algonquin Road
  Schaumberg, IL 60196
Baron Capital, Inc.(5)......................                   6,135,100           18.38%
  767 Fifth Avenue, 24th Floor
  New York, NY 10153
Hughes Communications Satellite Services, Inc.(6)             11,566,622           30.88%
  Building S66/D468
  Post Office Box 92424
  Los Angeles, CA 90009
XM Ventures(7)..............................                   6,479,443           16.35%
  c/o Noah Samara, as trustee
  2400 N St., N.W.
  Washington, DC 20037
Directors and Executive Officers
Douglas I. Brandon(8).......................                       5,000               *
Robert L. Goldsmith(9)(10)..................                     151,357               *
Pradeep P. Kaul(8)..........................                       6,000               *
Billy J. Parrott(8)(11).....................                      17,500               *
Gary M. Parsons(9)(10)......................                     450,990            1.39%
Walter V. Purnell, Jr.(9)(10)(12)...........                     112,387               *
Andrew A. Quartner(8)(13)...................                      21,000               *
Jack A. Shaw(8).............................                       6,000               *
Roderick M. Sherwood III(8).................                       6,000               *
Michael T. Smith(8).........................                       7,000               *
Randy S. Segal(9)(10).......................                     161,841               *
W. Bartlett Snell(10).......................                      40,000               *
All Directors and Executive Officers as a group (12
  persons)(8)(9)(10)........................                     985,075            3.03%
- -----------
  *  Less than 1%
</TABLE>


                                        3

<PAGE>



(1)      Certain  holders  of common  stock,  including  each of the  beneficial
         owners of more  than 5% of the common stock ("5% Stockholders")  listed
         in the table  are parties to a  stockholders'  agreement dated December
         1, 1993 (the "Stockholders'  Agreement").  The 5% Stockholders who are
         parties to  the  Stockholders'  Agreement may be deemed to constitute a
         group having  beneficial  ownership of all common stock held by members
         of  such  group.   See  "Certain   Relationships   and   Related  Party
         Transactions." Each such 5% Stockholder disclaims  beneficial ownership
         as to shares of common stock held by other 5% Stockholders.

(2)      Through  its  subsidiaries,   Transit  Communications,   Inc.  (681,818
         shares),  Satellite  Communications  Investments Corporation (1,113,135
         shares) and Space Technologies Investments,  Inc. (1,206,192).  Transit
         Communications,  Inc.  is  indirectly  80%-owned  by  LIN  Broadcasting
         Corporation,   which  is  an  indirect  subsidiary  of  AT&T  Wireless.
         Satellite Communications Investments Corporation and Space Technologies
         Investments, Inc. are direct or indirect subsidiaries of AT&T Wireless.

(3)      Singapore  Telecom  is  approximately  80%-owned  by  Temasek  Holdings
         (Private) Ltd., a Singapore holding company that is wholly owned by the
         Government of  Singapore.   Includes  812,500  shares  of common  stock
         issuable  upon  exercise of warrants  issued  in  connection  with  the
         guarantees  of  the  bank financings.

(4)      Motorola, Inc. has granted to the Underwriters an option to purchase up
         to 1,050,000 shares of common stock to cover overallotments.  If all of
         such  shares are sold by  Motorola,  Motorola  would  beneficially  own
         5,470,532 shares representing approximately 16.8% of our common stock.

(5)      Includes  812,500  shares of common  stock  issuable  upon  exercise of
         warrants   issued  in  connection  with  the  guarantees  of  the  bank
         financings.

(6)      Hughes Communications Satellite Services, Inc. ("HCSSI") is an indirect
         wholly-owned  subsidiary of Hughes, which is a wholly-owned  subsidiary
         of General Motors  Corporation.  Includes 25,000 shares of common stock
         issuable upon exercise of warrants issued to HCSSI on January 19, 1996,
         in connection  with a prior interim  financing  facility  guarantee and
         4,875,000 shares of common stock issuable upon exercise warrants issued
         in connection with the bank financings.

(7)      Information about XM Ventures is as of July 7, 1999. Excludes 2,134,801
         shares  that we  have  agreed  to  issue  to XM  Ventures,  subject  to
         stockholder  approval.  If such  shares are issued to XM  Ventures,  XM
         Ventures  would  beneficially  own  approximately  20.92% of our common
         stock.

(8)      Includes  shares  issuable  upon the exercise of options  granted under
         American  Mobile's Stock Option Plan for  Non-Employee  Directors which
         options  are vested and  exercisable  within  sixty days after June 30,
         1999, subject to compliance with applicable securities laws.


                                        4

<PAGE>



(9)      Includes  shares  owned  through American Mobile's matching 401(k) Plan
         and/or Employee Stock Purchase Plan.

(10)     Includes  shares  issuable  upon the exercise of options  granted under
         American  Mobile's  1989  Employee  Stock Option Plan which options are
         vested and exercisable  within sixty days after June 30, 1999,  subject
         to compliance with applicable  securities laws. Also includes shares of
         restricted  stock awarded under  American  Mobile's 1989 Employee Stock
         Option Plan, which are subject to a number of conditions of forfeiture.

(11)     Includes  7,500  shares owned by Private  Networks,  Inc., a company in
         which  Mr.  Parrott  owns a  one-third  equity  interest.  Mr.  Parrott
         disclaims beneficial ownership as to all such shares of common stock.

(12)     Includes  200  shares  owned by Mr.  Purnell's  wife,  as to which  Mr.
         Purnell disclaims beneficial ownership.

(13)     Includes  1,050  shares  owned by trusts for the benefit of each of Mr.
         Quartner's  three children,  of which Mr. Quartner is trustee,  and 100
         shares owned by Mr. Quartner's wife. Mr. Quartner disclaims  beneficial
         ownership as to all such shares of common stock.


            PROPOSAL 1. APPROVAL OF ISSUANCE OF STOCK TO XM VENTURES
            --------------------------------------------------------

The Exchange Transaction
- ------------------------

On July 7, 1999, the Company acquired from XM Ventures,  a trust  established by
WorldSpace,  Inc. ("WorldSpace"),  all of WorldSpace's debt and equity interests
in XM Satellite Radio Holdings, Inc. ("XM Radio"), other than a $75 million loan
from WorldSpace to XM Radio, in exchange for approximately 8.6 million shares of
the Company's Common Stock (the "Exchange Transaction").  Concurrently with this
transaction,  XM Radio issued $250 million of subordinated  convertible notes to
several  new  strategic  and  financial  investors,   including  General  Motors
Corporation  ("General  Motors"),   Clear  Channel  Investments,   Inc.  ("Clear
Channel"),  DIRECTV Enterprises,  Inc.  ("DIRECTV"),  Telcom Ventures,  Columbia
Capital and Madison  Dearborn  Partners (the "Private  Placement").  Immediately
thereafter,  XM Radio  reorganized  its  capital  structure.  XM Radio  used $75
million of the proceeds from these notes to repay the  outstanding  loan payable
to WorldSpace. The foregoing transactions are referred to herein collectively as
the "Transaction."

At the closing of the Exchange Transaction,  the Company issued 6,479,443 shares
of Common Stock to XM Ventures  and now holds 100% of XM Radio's  Class B common
stock,  which are the only shares of XM Radio's capital stock  outstanding.  The
Company also agreed,  subject to  stockholder  approval,  to issue the remaining
2,134,801 shares to XM Ventures (the "Additional Issuance").


                                        5

<PAGE>




Vote Required
- -------------

The Company's  Common Stock is quoted on the Nasdaq National  Market.  Under the
rules of the  Nasdaq  National  Market,  the  Company  must  obtain  stockholder
approval  prior to the  issuance  of Common  Stock if (a) the  issuance  of such
securities  is in  connection  with the  acquisition  of the  stock or assets of
another  company  and (b)  either  (i) the  common  stock  to be  issued  in the
transaction  will have upon its  issuance  voting power equal to or in excess of
20% of the voting power of the Company's  common stock  outstanding  before such
issuance or (ii) the number of shares of common stock to be issued is or will be
equal to or in excess of 20% of the number of shares of common stock outstanding
before  such  issuance.  Accordingly,  the Company  must obtain  approval of the
Additional  Issuance  from its  stockholders  before  such  Additional  Issuance
occurs,  because the shares of Common Stock issued to XM Ventures at the closing
of the  Exchange  Transaction,  together  with  the  Additional  Issuance,  will
represent  more than 20% of the voting  power of the  Company's  Common Stock or
more than 20% of the number of shares of Common Stock  outstanding prior to such
Additional Issuance.

The affirmative vote of a majority of the total votes cast,  excluding shares of
Common  Stock  held by XM  Ventures,  is  required  to  approve  the  Additional
Issuance.  In  connection  with  the  Exchange   Transaction,   the  holders  of
approximately 74% of the Company's Common Stock (Hughes Communications Satellite
Services,  Inc., Motorola,  Inc., Singapore  Telecommunications  Limited, BAMCO,
Inc.  and AT&T  Wireless  Services,  Inc.)  have  agreed to vote in favor of the
Additional Issuance. Such shares of Common Stock will be sufficient to establish
a quorum and to approve the  Additional  Issuance  without the vote of any other
stockholder.

The  Board of  Directors  unanimously  approved  the  Exchange  Transaction  and
recommends that stockholders approve the Additional  Issuance.  Stockholders are
not being asked to approve the Exchange Transaction.  A failure of the Company's
stockholders  to approve the Additional  Issuance will not affect the closing of
the Exchange Transaction.

The  Exchange  Transaction  had a dilutive  effect on the  voting  rights of the
holders of the Company's Common Stock. As a result of the Exchange  Transaction,
assuming  stockholder  approval of the  Additional  Issuance,  XM Ventures  will
beneficially own  approximately  20.9% of the Company's Common Stock outstanding
as of such date,  assuming  no  additional  stock is issued  prior to such date.
Although  the Company  will not be required to make the  Additional  Issuance if
stockholder approval is not received,  any failure by the Company to obtain such
approval  will not affect the  survival or validity of its  representations  and
warranties or covenants to  WorldSpace.  WorldSpace  will have a cause of action
against  the  Company  for  damages  caused  by a breach by the  Company  of its
representations  and  warranties and covenants and will be entitled to indemnity
for all  reasonable  costs and  expenses  (including  legal  fees)  incurred  by
WorldSpace in prosecuting such an action.

                                        6

<PAGE>




Background of the Company's Investment in XM Radio and Reasons for the
- ----------------------------------------------------------------------
Exchange Transaction
- --------------------

In  December  1992,  the  Company  formed a new,  wholly  owned  subsidiary,  XM
Satellite Radio Inc. ("XMSR",  formerly American Mobile Radio Corporation),  for
the purpose of procuring a digital audio radio service license ("DARS") from the
Federal Communication Commission ("FCC"). XMSR's business activity from December
1992 through 1996 was  insignificant.  In May 1997,  the Company  formed another
subsidiary,  XM Radio  (formerly AMRC Holdings  Inc.),  as a holding company for
XMSR.  XM Radio  owns all of the  outstanding  stock of XMSR.  Also in May 1997,
pursuant to various financing agreements among the Company, WorldSpace, XMSR and
XM Radio, WorldSpace acquired 20% of the voting interest in XM Radio, as well as
certain options to acquire additional capital stock of XM Radio, and also agreed
to provide  additional  loans to fund XMSR's bid for a DARS license.  In October
1997, the FCC awarded XMSR one of two DARS licenses,  in exchange for payment to
the FCC of the approximately $90 million bid at the DARS license auction.

In approving the Exchange Transaction, the Board of Directors concluded that its
interest in XM Radio offered potentially significant future value to the Company
and its  stockholders,  and that such  potential  value would  increase with the
increased  business  potential  of XM  Radio.  In order to  develop  and offer a
satellite-based  commercial  digital radio service in accordance with XM Radio's
business  plan,  however,  XM Radio  requires  significant  additional  capital.
Although  the  Company has no legal  obligation  and does not intend to fund the
development of XM Radio's business, the Board of Directors noted that XM Radio's
ability to attract  additional  capital would be enhanced if new investors could
participate  in an equity  structure  in XM Radio  that  would not be diluted by
WorldSpace's ownership interests. By facilitating an infusion of new funding for
XM Radio,  the Board of Directors also believed that it could attract  investors
who would bring strategic and competitive advantages to XM Radio.

Following the Exchange  Transaction,  the Company owns all of the issued capital
stock of XM Radio. If all securities  convertible  into voting stock of XM Radio
were converted, the Company would own approximately 37% of the economic interest
and  approximately  62% of the voting interest in XM Radio.  The $250 million of
Series A subordinated  convertible  notes are convertible into either XM Radio's
Class A common stock or Series A convertible  preferred stock at the election of
the holders and, automatically, upon the occurrence of certain events, including
an initial public offering of XM Radio yielding gross proceeds in excess of $100
million and above a prescribed per share value. In addition,  the Class B common
stock of XM Radio  owned by the  Company is  convertible  on a one for one basis


                                        7

<PAGE>


into  Class A  common  stock,  as  follows:  (1) at any  time  at the  Company's
discretion,  (2) following XM Radio's initial public offering,  at the direction
of the holders of a majority of the then outstanding  shares of XM Radio's Class
A common stock (which  majority must include at least 20% of the public  holders
of Class A common stock),  and (3) on or after January 1, 2002, at the direction
of the  holders of a majority of the then  outstanding  shares of Class A common
stock.  Such conversion  will be effected only upon receipt of FCC approval.  In
the event of such a conversion of the Company's Class B common stock of XM Radio
into Class A common  stock,  the Company's  voting  interest in XM Radio will be
reduced to approximately 37%.

The Company also is a party to a shareholders' agreement containing, among other
provisions, restrictions on the ability of the Company to transfer any shares of
XM Radio's  common  stock and an  agreement  relating to the  composition  of XM
Radio's  board  of  directors.  Additional  information  regarding  the XM Radio
shareholders'  agreement is included in the Company's Current Report on Form 8-K
dated July 9, 1999 and  incorporated by reference in this proxy  statement.  See
"Where to Get Additional Information."

Opinion of Bear Stearns
- -----------------------

American Mobile engaged Bear,  Stearns & Co. Inc.  ("Bear  Stearns") to render a
fairness  opinion in  connection  with the  Transaction  based on Bear  Stearns'
experience and expertise,  particularly in providing  advice to companies in the
technology and telecommunications  industries, as well as on Bear Stearns' prior
investment  banking  relationship  and familiarity  with American  Mobile.  Bear
Stearns  is an  internationally  recognized  investment  banking  firm  that has
substantial experience in transactions similar to the Transaction. Bear Stearns,
as part of its  investment  banking  business,  is  continuously  engaged in the
valuation  of  businesses  and   securities  in  connection   with  mergers  and
acquisitions,   negotiated   underwritings,   competitive  biddings,   secondary
distributions  of  listed  and  unlisted  securities,   private  placements  and
valuations for corporate and other purposes.

On June 7, 1999, Bear Stearns  delivered to American Mobile's Board of Directors
its oral opinion  (subsequently  confirmed in writing) to the effect that, as of
the date thereof, and subject to the assumptions, qualifications and limitations
set forth  therein,  the  consideration  to be received  by  American  Mobile in
exchange  for American  Mobile's  issuance of Common Stock to XM Ventures in the
Transaction  (collectively,  the  "Consideration")  was fair, as a whole, from a
financial  point of view, to the  unaffiliated  public  stockholders of American
Mobile.

The full text of Bear  Stearns'  opinion  dated as of June 7,  1999,  which sets
forth  the  assumptions  made,   matters   considered  and   qualifications  and
limitations on the review undertaken by Bear Stearns,  is incorporated herein by
reference.  The summary of Bear Stearns' opinion set forth below is qualified in


                                        8

<PAGE>


its entirety by reference to the full text of such opinion, which is attached as
Appendix A to this Proxy  Statement.  American Mobile  stockholders are urged to
read carefully Bear Stearns' opinion in its entirety.

In reading the  discussion  of such fairness  opinion set forth below,  American
Mobile stockholders should be aware that Bear Stearns' opinion:

o    was provided to the American Mobile Board of Directors for its sole benefit
     and use and was directed  only to the fairness of the  Consideration,  as a
     whole,  from  a  financial  point  of  view,  to  the  unaffiliated  public
     stockholders of American Mobile;

o    did  not  constitute  a  recommendation  to  the  American  Mobile Board of
     Directors in connection with the Transaction;

o    did not address any other  transactions  or arrangements to be entered into
     or payments to be made, directly or indirectly, by or to American Mobile or
     any other person as part of, or concurrently with, the Transaction;

o    did not address the merits of the underlying  business decision by American
     Mobile  to  engage  in the  Transaction  or the price or range of prices at
     which shares of American  Mobile  common stock may trade  subsequent to the
     announcement or consummation of the Transaction; and

o    did not constitute a recommendation to any holder of American Mobile Common
     Stock as to how to vote in connection with the Additional Issuance,  or any
     matter related thereto.

Although Bear Stearns evaluated the fairness of the  Consideration,  as a whole,
from a financial  point of view,  to the  unaffiliated  public  stockholders  of
American Mobile, the Consideration  itself was determined by American Mobile and
WorldSpace through arm's- length  negotiations.  Bear Stearns provided advice to
American Mobile during the course of such negotiations.  American Mobile did not
provide specific instructions to, or place any limitations on, Bear Stearns with
respect to the  procedures  to be followed or factors to be  considered by it in
performing its analyses or providing its opinion.

In the course of its analyses for  rendering its opinion,  Bear  Stearns,  among
other things:

o    reviewed the June 5, 1999 draft Exchange Agreement;

o    reviewed the  June 5, 1999 draft Summary of Principal Terms and Conditions,
     Proposed Issuance of Subordinated Convertible Notes;

o    reviewed the June 6, 1999 draft Note  Purchase  Agreement by and between XM
     Radio and the investors named therein;

                                        9

<PAGE>



o    reviewed  the  June 4, 1999 draft Amendment No. 1 to the Bridge, Additional
     Amounts and Working Capital Loans;

o    reviewed  American  Mobile's  Annual  Reports  to  Shareholders  and Annual
     Reports on Form 10-K for the fiscal  years ended  December 31, 1996 through
     1998, and its Quarterly  Report on Form 10-Q for the period ended March 31,
     1999;

o    reviewed   certain   operating   and   financial   information,   including
     projections,  provided to it by management of American  Mobile and XM Radio
     relating to American  Mobile's  and XM Radio's  respective  businesses  and
     prospects;

o    met with certain  members of the senior  managements of American Mobile and
     XM  Radio  to  discuss  the  respective  operations,  historical  financial
     statements and future prospects of American Mobile and XM Radio;

o    reviewed  the  historical  prices  and  trading volume of American Mobile's
     Common Stock;

o    reviewed publicly  available  financial data, stock market performance data
     and valuation  parameters of a company which Bear Stearns deemed  generally
     comparable to XM Radio;

o    reviewed the terms of a recent transaction involving the issuance of a note
     convertible into shares of XM Radio common stock; and

o    conducted such other studies, analyses,  inquiries and investigations as it
     deemed appropriate.

In the course of its  review,  Bear  Stearns  relied upon and  assumed,  without
independent  verification,  the accuracy and  completeness  of the financial and
other information,  including without limitation the projections  (including any
expected  synergies  reflected  therein),  provided to Bear  Stearns by American
Mobile and XM Radio.  With respect to American  Mobile and XM Radio's  projected
financial results,  Bear Stearns assumed that they have been reasonably prepared
on bases reflecting the best currently  available estimates and judgments of the
senior  managements  of American  Mobile and XM Radio as to the expected  future
performance of American Mobile and XM Radio, respectively.  Bear Stearns did not
assume  any  responsibility  for  the  independent   verification  of  any  such
information  or of the  projections  provided to Bear Stearns and further relied
upon the assurances of the senior  managements  of American  Mobile and XM Radio
that  they  are  unaware  of any  facts  that  would  make  the  information  or
projections  provided to Bear Stearns  incomplete or misleading.  In arriving at
its opinion,  Bear Stearns did not conduct a physical  inspection  of any of the
properties or assets, and did not perform or obtain any independent appraisal of
the assets or liabilities,  of American Mobile or XM Radio, nor was it furnished
with any  such  appraisals.  Bear  Stearns'  opinion  was  necessarily  based on
economic, market and other conditions, and the information made available to it,
as of the date thereof. Accordingly, although subsequent developments may affect


                                       10

<PAGE>



Bear Stearns' opinion, Bear Stearns undertook no obligation to update, revise or
reaffirm its opinion.  In rendering its opinion,  Bear Stearns  assumed that the
Transaction  would be consummated on  substantially  the terms  described in the
draft  Exchange  Agreement and related  documents  that it reviewed as described
above.

Financial  Analysis of Bear  Stearns.  The  following is a brief  summary of the
- -------------------------------------
material  valuation,  financial  and  comparative  analyses  considered  by Bear
Stearns in connection with the rendering of Bear Stearns' opinion.  Such summary
does not purport to be a complete  description of the analyses  underlying  Bear
Stearns' opinion.

In performing its analyses,  Bear Stearns relied solely on the assumptions  made
by American  Mobile and XM Radio with respect to industry  performance,  general
business,  economic,  market and financial conditions and other matters, many of
which are beyond the control of Bear Stearns, American Mobile, and XM Radio. Any
estimates   contained  in  the  analyses  performed  by  Bear  Stearns  are  not
necessarily  indicative  of  actual  values  or  future  results,  which  may be
significantly   more  or  less   favorable  than  suggested  by  such  analyses.
Additionally,  estimates of the value of businesses or securities do not purport
to be appraisals or to reflect the prices at which such businesses or securities
might actually be sold. Accordingly,  such analyses and estimates are inherently
subject to substantial uncertainty. In addition, Bear Stearns' opinion was among
several  factors  taken  into  consideration  by the  American  Mobile  Board of
Directors in making its  determination to approve the Transaction.  Based on the
closing  stock price for American  Mobile common stock on June 4, 1999 of $16.06
per share,  the  Exchange  Transaction  implied  an equity  value of XM Radio of
$567.9 million or $696,652 per share.

Discounted  Cash Flow Analysis.  Bear Stearns  performed a discounted  cash flow
- -------------------------------
("DCF")  analysis of XM Radio  based on  projections  for the fiscal  years 1999
through 2008 provided by XM Radio. These projections reflected certain synergies
expected by management of XM Radio to be created through  distribution and other
agreements with General Motors,  DIRECTV, and Clear Channel  (collectively,  the
"Strategic  Partners").  XM Radio's  management  prepared  an  "optimistic"  and
"conservative"  case  regarding the potential  impact of such  agreements.  Bear
Stearns relied on the "conservative"  case for this analysis.  Bear Stearns used
discount  rates of a range  of 25% to 30%,  based  on a  satellite  broadcasting
industry  weighted  average cost of capital.  In performing  its analysis,  Bear
Stearns used terminal EBITDA multiples of 7.0x to 10.0x.  Bear Stearns added the
present  values of the  discounted  free cash flows to the present values of the
terminal values to arrive at a range of implied  enterprise  values of XM Radio.
Bear  Stearns  then  deducted  long-term  debt  and  added  cash to the  implied
enterprise  values  of XM Radio to arrive  at a range of  equity  values  for XM
Radio.  This  analysis  implied an equity value per share range of $1,491,888 to
$3,240,887.

Analysis of Precedent XM Radio  Transaction.  Bear Stearns reviewed and analyzed
- -------------------------------------------
the financial  terms of a recent  transaction  involving  securities of XM Radio
(the "Precedent XM Radio  Transaction") and compared the financial terms of such


                                       11

<PAGE>


transaction  to those of the  Transaction  for  purposes of this  analysis.  The
Precedent XM Radio Transaction was American Mobile's issuance of a $21.5 million
note to an investor  convertible  into 24.5 shares of XM Radio common stock held
by American  Mobile.  Bear  Stearns  reviewed  the  consideration  given and the
conversion ratio in the Precedent XM Radio Transaction.  Bear Stearns noted that
the  Precedent XM Radio  Transaction  was not identical to the  Transaction  and
that,   accordingly,   any  analysis  of  the  Precedent  XM  Radio  Transaction
necessarily involved complex considerations and judgments concerning differences
in value and  consideration.  Bear  Stearns'  analysis of the Precedent XM Radio
Transaction  indicated  that the  implied  conversion  price  per  share for the
investor's XM Radio convertible note was $875,000 per share.

Analysis of Publicly Traded Company. Bear Stearns compared certain operating and
- -----------------------------------   financial  information  for  XM  Radio  to
certain  publicly  available   operating,   financial,   trading  and  valuation
information of CD Radio, Inc.  ("Comparable  Satellite  Broadcasting  Company").
Although  Bear  Stearns  used this company for  comparison  purposes,  it is not
identical to XM Radio.  Bear Stearns'  analysis  indicated  that the  Comparable
Satellite  Broadcasting  Company's  enterprise  value  to 2003,  2004,  and 2005
estimated   revenue  yielded  forward   multiples  of  2.3x,   1.1x,  and  0.7x,
respectively.  The Comparable Satellite  Broadcasting Company's enterprise value
to 2004 and 2005 estimated  EBITDA yielded  forward  multiples of 3.8x and 1.5x,
respectively.  Bear Stearns  applied a 20% discount to the Comparable  Satellite
Broadcasting  Company's  forward  multiples  to reflect  XM  Radio's  additional
financing risk,  potential time to market delay and the  incremental  capital CD
Radio has invested in its  operations to date.  After the discount,  the implied
forward revenue  multiples were 1.8x,  0.9x, and 0.6x for 2003,  2004, and 2005,
respectively,  and the implied  forward EBITDA  multiples were 3.0x and 1.2x for
2004 and 2005, respectively. Application of XM Radio's projected revenue yielded
a range of per share values of $682,649 to $1,335,237. Application of XM Radio's
projected EBITDA yielded a range of per share values of $966,524 to $1,376,449.

Has/Gets Analysis.  Based on a DCF analysis, Bear Stearns examined the projected
- ------------------
per share value held by American Mobile stockholders pre- and post- Transaction.
The American Mobile DCF value was derived using a range of discount rates of 16%
to 20% and terminal EBITDA multiples of 4.0x to 7.0x. The XM Radio DCF value was
derived  using a range  of  discount  rates  of 25% to 30% and  terminal  EBITDA
multiples  of  7.0x to  10.0x.  Total  pre-Transaction  value  held by  American
Mobile's  shareholders  was determined by summing their 100% ownership  stake in
American  Mobile  with  their  21.5%  ownership   interest  in  XM  Radio.   The
pre-Transaction  DCF value of XM Radio was derived using  stand-alone  financial
projections  provided  by XM Radio  without  giving  effect to  agreements  with
Strategic  Partners.  Total  post-Transaction  value  held  by  American  Mobile
stockholders  was  determined  by summing  their  reduced  ownership in American
Mobile of 83.3% with their increased  ownership stake in XM Radio of 30.7%.  The
post- Transaction DCF value of XM Radio was derived using financial  projections
provided  by  XM  Radio,  which  included  operating  synergies  resulting  from
agreements  with  the  strategic  partners.  This  analysis  suggested  that the


                                       12

<PAGE>


Transaction  should  result in  accretion  in total value to  American  Mobile's
stockholders  when the  operating  synergies  from the  Strategic  Partners  are
included in the value of XM Radio.

Impact of Strategic Partners.  Bear Stearns examined the financial impact of the
- -----------------------------
Strategic Partners on XM Radio. As part of Bear Stearns'  analysis,  it reviewed
and compared XM Radio's  financial  projections  pre-Transaction,  reflecting no
Strategic   Partner   impact,    with   XM   Radio's    financial    projections
post-Transaction,  reflecting  the  operational  agreements  with and  potential
enhancements  from the Strategic  Partners.  XM Radio's  management  prepared an
"optimistic"  and  "conservative"  case  regarding the  potential  impact of the
Strategic  Partners.  Bear Stearns  relied on the  "conservative"  case for this
analysis.  Based on DCF analyses,  Bear Stearns examined the enterprise value of
XM  Radio  pre-and  post-Transaction.   The  DCF  analysis  indicated  that  the
enterprise  value of XM Radio  increased due to the involvement of the Strategic
Partners.

The preparation of a fairness  opinion is a complex process and involves various
judgments and determinations as to the most appropriate and relevant assumptions
and financial  analyses and the  application  of these methods to the particular
circumstances  involved. Such an opinion is therefore not readily susceptible to
partial analysis or summary description, and taking portions of the analyses set
out above,  without  considering the analysis as a whole,  would, in the view of
Bear  Stearns,  create an  incomplete  and  misleading  picture of the processes
underlying  the analyses  considered in rendering  Bear Stearns'  opinion.  Bear
Stearns did not form an opinion as to whether any individual  analysis or factor
(positive or negative),  considered in isolation, supported or failed to support
Bear Stearns' opinion.  In arriving at its opinion,  Bear Stearns considered the
results of its separate analyses and did not attribute  particular weight to any
one analysis or factor  considered by such firm. The analyses  performed by Bear
Stearns,  particularly  those  based  on  estimates  and  projections,  are  not
necessarily  indicative of actual values or actual future results,  which may be
significantly  more or less  favorable  than  suggested by such  analyses.  Such
analyses were prepared solely as part of Bear Stearns'  analyses of the fairness
of the  Consideration,  as a whole,  from a  financial  point  of  view,  to the
unaffiliated public stockholders of American Mobile.

Fee  Arrangements.  Pursuant  to the terms of its  engagement  letter  with Bear
- -----------------
Stearns, American Mobile paid a customary fee to Bear Stearns in connection with
the  delivery  of Bear  Stearns'  opinion.  American  Mobile has also  agreed to
indemnify  Bear Stearns  against  certain  liabilities  in  connection  with its
engagement, including certain liabilities under the federal securities laws.

Bear Stearns has been  previously  engaged by American Mobile to provide certain
investment  banking and financial  advisory services in connection with American
Mobile's  acquisition  of ARDIS Company in 1998 and to act as lead manager on an
offering  of senior  notes and  warrants  in 1998,  for which (in each  case) it


                                       13

<PAGE>


received customary compensation. Bear Stearns is also acting as lead manager for
American  Mobile's  pending  offering  of up to 7 million  shares of its  Common
Stock. In the ordinary  course of business,  Bear Stearns may actively trade the
equity  securities of American Mobile for its own account and for the account of
its customers and, accordingly, may at any time hold a long or short position in
such  securities.  Bear Stearns also acted as exclusive joint placement agent on
the Private Placement and received customary compensation from XM Radio for such
services.  American Mobile and XM Radio expressly waived any actual or potential
conflicts of interest in connection  with Bear  Stearns'  engagement by American
Mobile to render its fairness opinion, on the one hand, and its engagement by XM
Radio to act as exclusive joint placement agent in the Private Placement, on the
other hand.

Pro Forma Summary Financial and Other Data
- ------------------------------------------

The following  summary pro forma  financial  information  gives effect to the XM
Radio  transactions  and the related XM Radio financing as if such  transactions
had been  consummated  on March 31, 1999 in the case of the  Unaudited Pro Forma
Consolidated  Condensed  Balance Sheet of American  Mobile,  and on January 1 of
each  of  the  periods  presented  in  the  case  of  the  Unaudited  Pro  Forma
Consolidated  Condensed  Statements of Operations  of American  Mobile.  The pro
forma  operating  results  for the year ended 1998 also give effect to the March
31, 1998  acquisition of ARDIS Company and  concurrent  units offering of senior
notes and warrants as if such  transactions  had been  consummated on January 1,
1998.  The summary pro forma  consolidated  condensed  financial  information is
presented for  illustrative  purposes only and is not necessarily  indicative of
what American Mobile's actual financial position and results of operations would
have  been had the  above-referenced  transactions  been  consummated  as of the
above-referenced  dates or of the  financial  position or results of  operations
that may be reported by American Mobile in the future.

The  following  data should  read in  conjunction  with the pro forma  financial
information and American Mobile's Consolidated  Financial Statements and related
notes  and XM  Radio's  Consolidated  Financial  Statements  and  related  notes
includes  in the  Company's  Current  Report on Form 8-K dated  July 9, 1999 and
incorporated by reference herein. See "Where to Get Additional Information."


                                       14

<PAGE>


<TABLE>


<CAPTION>

                                                      For the Three Months                  For the Year Ended
                                                      Ended March 31, 1999                   December 31, 1998
                                               ---------------------------------- ------------------------------------

                                               (Dollars in  thousands, except subscribers and revenue per unit)

Statement of Operations Data:
Revenue:
<S>                                                        <C>                                     <C>
     Services                                              $   16,164                              $  67,396
     Sales of equipment                                         4,066                                 29,757
                                                           ----------                              ---------
          Total revenue                                        20,230                                 97,153

Operating loss                                                (30,573)                              (112,340)
Net loss                                                      (47,010)                              (185,365)

Other Financial and Operating
Data:
Number of subscribers (end of period)                         113,000                                105,700
Average monthly revenue per unit                                   49                                     60
EBITDA                                                        (16,107)                               (53,047)
Depreciation and amortization                                  14,466                                 59,293
Capital expenditures                                           53,173                                 57,699
</TABLE>

<TABLE>
<CAPTION>

                                                      As of March 31, 1999
                                               ----------------------------------
                                                         (in thousands)
Balance Sheet Data:
<S>                                                        <C>
Cash and cash equivalents                                  $  175,323
Restricted investments                                        109,661
Property and equipment, net                                   239,615
Total assets                                                  927,868
Total debt                                                    776,307
Total stockholders' equity                                     51,244

</TABLE>


Overview of XM Radio
- --------------------

XM Radio is a development stage company seeking to become a nationwide  provider
of digital quality audio entertainment and information  programming  transmitted
directly by satellites to car, home, and portable  radios.  XM Radio owns one of
two FCC licenses to provide satellite digital audio radio service for the United
States.  XM Radio is developing  its service,  which it will call "XM Radio," to
provide a wide  variety of music,  news,  talk,  sports,  and other  programming
offering up to 100 distinct  channels.  XM Radio believes that customers will be
attracted to the broad  offering of formats and the  service's  digital  quality
sound, coast-to-coast coverage, and text display features.

XM Radio currently is  constructing  its satellite  system and contracting  with
third-party  programmers,  vendors, and other partners.  Key milestones achieved
include the following:


                                       15

<PAGE>



                  o Raised approximately $331 million of capital to date, net of
                    expenses and repayment of debt, including recent investments
                    by several strategic and financial investors;

                  o Long-term  agreement  with the  OnStar  division  of General
                    Motors  Corporation  covering the installation and exclusive
                    marketing  and  distribution  of  XM  Radio  service  in  GM
                    vehicles;

                  o Contract with Hughes Space and Communications International,
                    Inc. for delivery and launch of two high-powered satellites;

                  o Agreement with  STMicroelectronics,  a leading digital audio
                    chipset  manufacturer,  for the  design  and  production  of
                    chipsets for XM radios;

                  o Contracts with Alpine Electronics,  Pioneer, SHARP and Delco
                    Electronics to manufacture and distribute XM radios; and

                  o Agreements  with  leading  specialty  programmers  including
                    Black    Entertainment    Television,     Inc.,    Bloomberg
                    Communications  Inc.,  Cable News Network LP, National Cable
                    Satellite  Corporation  (C-SPAN),  AsiaOne Network,  L.L.C.,
                    Hispanic   Broadcasting   Corporation   (formerly   Heftel),
                    One-on-One  Sports Radio Network,  Inc., Radio One, Inc. and
                    Salem Communications Corporation.

XM Radio is designing its system to provide  satellite  radio to the continental
United States and coastal waters using S-Band radio frequencies allocated by the
FCC for satellite  radio.  The XM Radio system will be capable of providing high
quality  satellite  radio services to mobile XM radios in  automobiles,  trucks,
recreation  vehicles  and  pleasure  craft,  as well as to fixed or  portable XM
radios in the home, office or other fixed locations.

XM Radio's  principal  executive  offices are located at 1250 23d Street,  N.W.,
Washington, D.C. 20037, telephone: (202) 969-7100.

Selected Financial Data
- -----------------------

Set  forth  below  is  selected  financial  data for XM  Radio  for the  periods
indicated.  The selected  financial data should be read in conjunction  with the
consolidated  financial  statements  and  related  notes of XM  Satellite  Radio
Holdings Inc. and  Subsidiary  included in the Company's  Current Report on Form
8-K dated July 9, 1999 and  incorporated  by reference in this proxy  statement.
See "Where to Get Additional Information."










                                       16

<PAGE>




<TABLE>
<CAPTION>

                                      December 15, 1992
                                     (Date of Inception)          Years Ended               Three Months Ended
                                       to December 31,            December 31,                    March 31,
                                       ---------------            ------------                ---------

                                            1998               1997           1998            1998         1999
                                            ----               ----           ----            ----         ----
                                                         (In thousands, except share data)

Statements of Operations Data:

<S>                                       <C>                  <C>            <C>             <C>          <C>
Revenue                                   $       -            $       -      $       -       $       -    $       -
                                          ---------            ---------      ---------       ---------    ---------

Operating expenses:
   Research and development                   6,941                    -          6,941           1,933          748
   Professional fees                          6,332                1,090          5,242           1,050        1,297
   General and administrative                 4,030                   20          4,010             117        2,376
                                          ---------                   --          -----             ---        -----
   Total operating expenses                  17,303               (1,110)        16,193           3,100        4,421
                                          ---------              -------         ------           -----        -----
Interest income (expense), net                 (523)                (549)            26              --           54
Net loss                                  $ (17,826)             $(1,659)      $(16,167)        $(3,100)     $(4,367)
                                          =========              =======       =========        =======      =======
Net loss per share                        $(146,115)            $(13,941)     $(129,336)       $(24,800)    $(34,936)
                                          =========             ========      ==========       ========     ========
Weighted average shares used in
   computing net loss per share -
   basic and diluted                            122                  119            125             125          125
</TABLE>


<TABLE>
<CAPTION>

                                             December 31,       December 31,      March 31, 1999
                                                1997               1998             (Unaudited)
                                             ------------       ------------      --------------
                                                    (In thousands)


Balance Sheets Data:

<S>                                           <C>              <C>                <C>
Cash and cash equivalents..                   $     1          $     310          $   3,442
System under construction..                    91,932            169,029            219,455
Total assets...............                    91,933            170,485            224,405
Total debt.................                    82,504            140,298             78,906
Total liabilities..........                    82,944            177,668            235,955
Stockholders' equity (deficit)                  8,984            (7,183)           (11,550)

</TABLE>


                                       17

<PAGE>



XM Radio -- Management's Discussion and Analysis of Financial Condition
- -----------------------------------------------------------------------
and Results of Operations
- -------------------------

XM Radio is a  development  stage  company  engaged in the  construction  of its
satellite  radio  service.  As such,  it  currently  generates no revenue and is
incurring significant  operating losses. Prior to the Exchange Transaction,  the
Company accounted for XM Radio according to the equity method of accounting.  As
a result of the Exchange  Transaction,  the Company will  consolidate XM Radio's
accounts and  operating  results with its own until such time,  if ever,  as the
Company no longer controls XM Radio.  XM Radio incurred  aggregate net losses of
approximately  $1.7 million from its inception through December 31, 1997, and an
additional   $20.5  million  in  the  15-month  period  ended  March  31,  1999.
Additionally,  in accordance with generally accepted accounting principles,  the
Company restated its financial  statements for the year ended December 31, 1998,
and the quarter ended March 31, 1999,  to effect its share of XM Radio's  losses
based on our voting  equity  interest in XM Radio  during  those  periods.  This
resulted in the Company's recording additional net losses of approximately $12.6
million for the year ended  December 31, 1998,  and $3.5 million for the quarter
ended March 31, 1999.

XM Radio has raised  approximately  $331.0  million  of capital to date,  net of
expenses and repayment of debt,  including  $250.0  million of gross proceeds of
subordinated  convertible  notes  issued on July 7, 1999.  These funds have been
used to acquire XM Radio's FCC license,  make required payments under XM Radio's
satellite contract with Hughes, and for working capital and operating  expenses.
Of the funds  raised by XM Radio  prior to July 7, 1999,  the  Company  provided
approximately $1.7 million, $21.4 million was provided by the XM Note Receivable
described under the caption  "Management's  Discussion and Analysis of Financial
Condition and Results of Operations - Liquidity and Capital Resources" contained
in the  Company's  annual  report on Form 10-K for the year ended  December  31,
1998, and the remainder was provided by WorldSpace.  On July 7, 1999 the Company
acquired  WorldSpace's  debt and equity interests in XM Radio,  other than a $75
million loan from  WorldSpace  to XM Radio,  in exchange for  approximately  8.6
million  shares  of  the  Company's   common  stock.   Concurrently   with  this
transaction,  XM Radio issued $250 million of subordinated  convertible notes to
several new strategic and financial investors.  XM Radio used $75 million of the
proceeds from the notes to repay the outstanding loan payable to WorldSpace.  As
a  result  of  these  transactions,  the  Company  owns  all of the  issued  and
outstanding  stock of XM Radio,  although  several large notes  convertible into
equity of XM Radio are outstanding.  WorldSpace no longer owns any direct equity
or debt interest in XM Radio. The XM Note Receivable  (which also is convertible
into XM Radio stock) presently has an outstanding balance of approximately $21.7
million,  including  accrued interest.  Assuming a subsequent  conversion of all
outstanding  convertible  notes of XM Radio into voting stock, the Company would
own approximately 37% of the economic interest in XM Radio.


                                       18

<PAGE>



XM Radio currently estimates that it will require  approximately  $750.0 million
in addition  to the  amounts it has raised thus far to develop and  commercially
launch its system,  which is currently  expected in 2001. Even after its service
is launched  commercially,  XM Radio  anticipates  that it will need substantial
further  funding  to cover its cash  requirements  before  it begins  generating
positive cash flow from  operations.  XM Radio's actual  financing  requirements
will depend on how the business  develops  over the next two years and cannot be
estimated  at the present  time.  XM Radio's  primary uses of funds will include
satellite  construction  and launch,  launch and  in-orbit  insurance  premiums,
construction of its terrestrial  repeater  system,  development of the satellite
radio ground segment, and working capital and operating expenses.

XM Radio has  significant  payment  obligations  under a long-term  distribution
agreement with the OnStar  division of General Motors.  This agreement  provides
for the installation of XM radios in General Motors vehicles. During the term of
the agreement,  which expires 12 years from the commencement  date of XM Radio's
commercial  operations,  General  Motors  has  agreed to  distribute  XM Radio's
service to the exclusion of other S-band  satellite  digital radio services.  XM
Radio has significant  annual,  fixed payment  obligations to General Motors for
four  years  following   commencement  of  commercial  service.  These  payments
approximate $35 million in the aggregate during this period.  Additional  annual
fixed  payment  obligations  beyond the initial four years of the contract  term
range from less than $35 million to  approximately  $130 million  through  2009,
aggregating  approximately  $400  million.  In  order  to  encourage  the  broad
installation  of XM radios in General  Motors  vehicles,  XM Radio has agreed to
subsidize a portion of the cost of XM radios,  and to make incentive payments to
General  Motors when the owners of General  Motors  vehicles  with  installed XM
radios become  subscribers  for the XM Radio  service.  XM Radio must also share
with General Motors a percentage of the  subscription  revenue  attributable  to
General Motors  vehicles with  installed XM radios.  This  percentage  increases
until there are more than 8 million  General  Motors  vehicles with installed XM
radios.  The  agreement  is subject to  renegotiation  if,  four years after the
commencement  of XM Radio's  commercial  operations  and at  two-year  intervals
thereafter  GM does not achieve and maintain  specified  installation  levels of
General Motors vehicles capable of receiving XM Radio's  service,  starting with
1.24 million  units after four years,  and the lesser of 600,000  units per year
thereafter  and amounts  proportionate  to target market shares in the satellite
digital  radio service  market.  There can be no assurances as to the outcome of
any such renegotiation.

XM Radio expects to satisfy its future funding  requirements  by selling debt or
equity securities,  publicly and/or privately,  and by obtaining loans or credit
lines from banks or other financial institutions. Any such sale could reduce our
interest in XM Radio.  In addition,  XM Radio plans to seek funds through vendor
financing  arrangements  in  connection  with  construction  of its  terrestrial
repeater system. XM Radio's projections  regarding its funding  requirements are
forward-looking,  and XM Radio's actual  requirements could vary materially from
its projections,  due to a variety of factors,  some of which are outside of the


                                       19

<PAGE>


control of XM Radio, including unexpected costs, unforeseen delays,  engineering
design  changes,  launch  failures,   satellite  anomalies,  adverse  regulatory
developments, or other unanticipated events.

The Company is not required to provide any additional  funding to XM Radio,  and
the Company expects that XM Radio will continue to obtain  substantially  all of
its  required  funding  from other  sources.  Accordingly,  the Company does not
expect that  development of the XM Radio business will have a material effect on
its consolidated liquidity, capital resources or cash flows.


Certain Transactions Involving the Exchange Transaction and XM Radio
- --------------------------------------------------------------------

Registration  Rights.  The Company is  obligated  to register  for resale,  on a
- ---------------------
delayed or continuous basis,  under the Securities Act of 1933, as amended,  the
shares of its Common Stock  acquired by XM Ventures or the holders of its Common
Stock in the Exchange Transaction.  The Company may suspend the effectiveness of
the  resale  registration  statement,  at its  option,  up to two  times  in any
consecutive 365-day period, for no more than 30 consecutive days per suspension,
separated,  in each case, by at least 60 days from any prior blackout period, in
the event of certain  significant  business  combinations  or  similar  material
transactions,  if (i) the Board of Directors determines,  in the exercise of its
reasonable  judgment,   that  disclosure  of  such  transaction  in  the  resale
registration  statement is not in the  Company's  best  interests,  and (ii) the
Company provides notice of such determination to XM Ventures.

Whenever  the  Company  proposes  to  register  any  of  its  securities  in  an
underwritten  offering  under the  Securities  Act,  whether  or not for its own
account,  on a form  that may also be used for the  registration  of the  shares
issued to XM Ventures in the  Exchange  Transaction,  XM Ventures  and the other
holders of common stock issued in the Exchange  Transaction may request that the
Company include,  or "piggyback," in such  registration all of the shares issued
to XM Ventures in the Exchange  Transaction.  The piggyback  registration rights
granted to XM Ventures are subject and  subordinate to the  registration  rights
under all of the Company's other existing  registration  rights  agreements with
other  parties.  In  addition,  XM  Ventures  may not  exercise  such  piggyback
registration  rights in the  Company's  first public  offering that occurs after
July 7, 1999.

In  addition,  beginning  on the  later  of July  7,  2001  or the  exercise  or
expiration of all demand  registration  rights under all of the Company's  other
existing  registration  rights  agreements  with other parties,  but in no event
later than July 7, 2002,  irrespective of whether all demand registration rights
under all of such  other  existing  registration  rights  agreements  with other
parties  have been  exercised or expired,  XM Ventures and the other  holders of
common  stock  issued  in the  Exchange  Transaction  shall be  entitled  to two
underwritten  demand  registrations  on customary  terms and  procedures.  These
demand  registrations  are  subject  to the  right  of the  Company's  Board  of


                                       20

<PAGE>


Directors to delay any such  registration  for up to 90 days upon its good faith
determination  that such  registration is not in the Company's best interests at
that time.

XM  Ventures   Transfer   Restrictions.   XM  Ventures  has  agreed  to  certain
- ---------------------------------------
restrictions  on the transfer of shares of Common Stock  received in  connection
with the Exchange Transaction. At the closing, XM Ventures was permitted to sell
or otherwise dispose of and/or distribute to certain  stockholders of WorldSpace
("WorldSpace Stockholders") and/or holders of options or other rights to acquire
an interest in WorldSpace  ("Option  Holders")  (if and when the Option  Holders
become  stockholders in WorldSpace) up to 1.7 million shares of Common Stock. On
or after the last day of each consecutive  3-month period following the closing,
XM Ventures may sell or otherwise dispose of and/or distribute to the WorldSpace
Stockholders  and/or  Option  Holders  (if and when such Option  Holders  become
stockholders  of  WorldSpace)  up to an  additional  20% of the acquired  Common
Stock.

XM Ventures  and each of the  WorldSpace  Stockholders  or Option  Holders  that
beneficially own (as determined under Rule 13d-3 of the Securities  Exchange Act
of 1934)  more  than 1% of the then  outstanding  shares of  Common  Stock  (the
"Significant  Stockholders"),  without  the prior  written  consent of  American
Mobile, which consent is not to be unreasonably  withheld, may not (i) knowingly
transfer  in a  directed  sale any of the  Common  Stock  held by them  to:  (A)
WorldSpace or any affiliate of WorldSpace  (other than a WorldSpace  Stockholder
or Option Holder in accordance  with the terms of the Exchange  Agreement);  (B)
any  alien  or  the  representative  of  any  alien;  or  (C)  any  corporation,
partnership,  or other legal entity of which more than one-fourth of the capital
stock or other ownership interests is owned of record or voted by aliens,  their
representatives,  or by a foreign government or representative  thereof; or (ii)
transfer,  in any single transaction or in any related series of transactions to
any  individual,  entity,  or group of individuals  or entities,  such number of
shares  of  Common  Stock  held by  them  constituting  5% or  more of the  then
outstanding shares of Common Stock.

XM Ventures Voting Restrictions. From July 8, 1999 until the first date on which
XM  Ventures  and the  Significant  Stockholders  hold less than 15% of the then
outstanding shares of Common Stock (the "Mirror Voting Period"), XM Ventures and
each Significant  Stockholder is obliged to, with respect to any vote or consent
by the  holders  of  Common  Stock  on any  matter,  be  present  in  person  or
represented  by proxy at any  meeting of the  American  Mobile  stockholders  to
consider  such matter,  and to vote such shares of Common Stock held by them, or
sign any such  consent,  in  proportion  to the votes or  consents  of all other
American Mobile stockholders voting on or consenting to such matter.

Following  the  expiration  of the Mirror  Voting  Period,  XM Ventures  and the
Significant  Stockholders  may vote the Common Stock held by XM Ventures and the
Significant   Stockholders,   respectively,   as  each  determines  in  its  own
discretion.


                                       21

<PAGE>



Other Information
- -----------------

Restated  financial  statements  of the  Company  for the years  ended  December
31,1998,  1997 and 1996 and the periods  ended March 31, 1999 and March 31, 1998
are included in the Company's  Current Report on Form 8-K dated July 9, 1999 and
incorporated by reference in this proxy statement.  See "Where to Get Additional
Information."

Certain  other  information  regarding  the  Company's  investment  in XM Radio,
including risks that may impair the value of the Company's  investment and other
transactions involving XM Radio, are included in the Company's Current Report of
Form 8-K  dated  July 9,  1999  and  incorporated  by  reference  in this  proxy
statement. See "Where to Get Additional Information."

                  The Board of Directors recommends a vote FOR
                    the Issuance of the Additional Issuance.


                                       22

<PAGE>



                     PROPOSAL 2. AMENDMENT TO THE COMPANY'S
                     --------------------------------------
                AMENDED AND RESTATED CERTIFICATE OF INCORPORATION
                -------------------------------------------------
                TO INCREASE THE NUMBER OF SHARES OF COMMON STOCK
                ------------------------------------------------
                             AUTHORIZED FOR ISSUANCE
                             -----------------------

On May 26, 1999,  the Board of Directors  approved an amendment to the Company's
Amended and  Restated  Certificate  of  Incorporation  to increase the number of
shares of  Common  Stock  authorized  for  issuance  from  75,000,000  shares to
150,000,000 shares.

As of July 14, 1999, there were 39,136,801  shares of the Company's Common Stock
issued and outstanding out of 75,000,000  authorized  shares of Common Stock. As
of July 14, 1999,  approximately  13,763,916  additional  shares of Common Stock
were  reserved for  issuance  pursuant to the  Company's  stock option plans and
other employee  benefit plans,  upon exercise of outstanding  warrants,  and for
issuance to XM Ventures under the Exchange Agreement.  In addition,  the Company
has  filed a  registration  statement  relating  to the  offer and sale of up to
7,000,000  newly issued  shares.  Consequently,  there are a total of 59,900,717
shares of Common Stock issued and  outstanding or reserved for future  issuance,
and  there  are  only  approximately   15,099,283  authorized  shares  remaining
available for future issuance. The Company's Amended and Restated Certificate of
Incorporation also presently authorizes 200,000 shares of Preferred Stock, which
will not be changed by the proposed amendment.

The  increase in the number of  authorized  shares of Common  Stock will provide
additional  authorized and unissued  shares which may be used by the Company for
any proper corporate purpose and without additional  stockholder approval unless
such  approval is required by federal or state law or the rules and  regulations
of The Nasdaq Stock Market National Market. Such purposes might include, without
limitation, issuance in public or private sales for cash as a means of obtaining
additional capital for use in the Company's business and operations, issuance as
part  or all  of the  consideration  required  to be  paid  by the  Company  for
acquisition of other  businesses or properties,  and possible  distributions  or
dividends  to  holders  of  Common   Stock.   Although  many  of  the  foregoing
transactions will not require additional  stockholder approval, the Company does
consider from time to time proposals or  transactions  involving the issuance of
additional shares of Common Stock or instruments convertible into or exercisable
for Common Stock.

The additional shares of Common Stock for which  authorization is sought will be
identical to the shares of Common Stock of the Company now  authorized.  Holders
of Common  Stock do not have  preemptive  rights  to  subscribe  for  additional
securities  that may be issued by the  Company.  Although  future  issuances  of
additional  shares of Common Stock will be  authorized by the Board of Directors
based  on  its  judgment  as to  the  best  interests  of the  Company  and  its
stockholders,  any such future  issuance of additional  authorized  shares would
have the  effect of  diluting  the voting  power per  share,  and could have the
effect of diluting the book value per share, of the outstanding shares of Common
Stock. In addition,  an increase in the authorized shares of Common Stock could,


                                       23

<PAGE>


in certain  instances,  render more  difficult or  discourage  a merger,  tender
offer, or proxy contest and thus  potentially  have an  "anti-takeover"  effect,
especially  if  additional  shares of Common  Stock were issued in response to a
potential  takeover.  Such an effect could deter certain  types of  transactions
that might be  proposed,  whether or not such  transactions  were favored by the
majority  of  stockholders,  and could  enhance  the  ability  of  officers  and
directors to retain their positions.

If the amendment is authorized, the text of Paragraph A of Article FOURTH of the
Company's Amended and Restated  Certificate of Incorporation  will be amended to
read as follows:

                  "A.  Authorized  Capital Stock.  The total number of shares of
         all classes of stock which the Corporation shall be authorized to issue
         shall  be  one  hundred  fifty  million  two  hundred  thousand  shares
         (150,200,000)  shares. One hundred fifty million  (150,000,000) of said
         shares  shall  be of a par  value  of  $.01  per  share  and  shall  be
         designated  common  stock  ("Common  Stock") and two  hundred  thousand
         (200,000)  of said shares shall be of a par value of $.01 per share and
         shall be designated Series Preferred Stock."

Recommendation and Vote Required
- --------------------------------

The affirmative  vote of the holders of two-thirds of the outstanding  shares of
Common Stock is required to authorize the proposed  amendment to the Amended and
Restated Certificate of Incorporation.

   The Board of Directors Recommends a Vote FOR the Approval of this Proposal.


                                  OTHER MATTERS
                                  -------------

The Board of Directors is not aware of any other  matters to be presented at the
special meeting.  If any other matter proper for action at the meeting should be
presented,   the  holders  of  the  accompanying  proxy  will  vote  the  shares
represented by the proxy on such matter in accordance  with their best judgment.
If any matter not proper for  action at the  meeting  should be  presented,  the
holders of the proxy will vote against consideration thereof or action thereon.

The Company  does not expect any  representative  of the  Company's  accountant,
Arthur Andersen LLP, to attend the meeting.

All shares represented by the accompanying  proxy, if the proxy is duly executed
and  received  by the Company at or prior to the  meeting,  will be voted at the


                                       24

<PAGE>


meeting in accordance with any  instructions  specified on such proxy and, where
no instruction is specified, as indicated on such proxy.

                       WHERE TO GET ADDITIONAL INFORMATION
                       -----------------------------------

The SEC allows the Company to  incorporate  by reference the  information  filed
with the SEC, which means that the Company can disclose important information to
you by  referring  you to  those  documents.  The  information  incorporated  by
reference is considered to be part of this proxy statement, and information that
the Company  files later with the SEC will  automatically  update and  supersede
this  information.  The Company  incorporates by reference the documents  listed
below  and any  future  filings  (File No.  0-23044)  we make with the SEC under
Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934:

         a.    our annual  report on Form 10-K for the year ended  December  31,
               1998;

         b.    our quarterly report on Form 10-Q for the quarter ended March 31,
               1999;

         c.    our  report on Form 8-K dated June 7, 1999 and filed with the SEC
               on June 9, 1999; and

         d.    our  report on Form 8-K dated July 9, 1999 and filed with the SEC
               on July 9, 1999.

You may request a copy of these  filings,  at no cost, by writing or telephoning
the Company at the following address:

                                   Randy Segal
                         Senior Vice President, General
                              Counsel and Secretary
                      American Mobile Satellite Corporation
                              10802 Parkridge Blvd.
                           Reston, Virginia 20191-5416
                                 (703) 758-6000

                                            By order of the Board of Directors,
                                            Randy S. Segal
                                            Senior Vice President and Secretary

Reston, Virginia
August 6, 1999


                                       25

<PAGE>



                                                                      Appendix A





                    [Letterhead of Bear, Stearns & Co. Inc.]


As of June 7, 1999

Board of Directors
American Mobile Satellite Corporation
10802 Parkridge Boulevard
Reston, VA  20191-5416
Attention:  Gary Parsons, Chairman

Gentlemen:

We understand  that, as more fully  described in the June 5, 1999 draft Exchange
Agreement (the "Exchange  Agreement")  by and among  American  Mobile  Satellite
Corporation  ("American  Mobile"),   WorldSpace,   Inc.  ("WorldSpace")  and  XM
Satellite  Radio  Holdings Inc. ("XM Radio"),  American  Mobile intends to issue
shares of common stock, par value $.01 per share, of American Mobile  ("American
Mobile Common  Stock") to XM Ventures,  a trust to be  established by WorldSpace
for the  benefit  of  WorldSpace  and/or the  stockholders  of  WorldSpace  (the
"Trust"),  in  exchange  for the XM  Interest  (as  defined  in and  more  fully
described in the Exchange  Agreement)  (the  "Purchase").  In  consideration  of
American  Mobile's  receipt of the XM Interest,  American Mobile would issue the
First Transfer (as defined in the Exchange Agreement) at the Closing (as defined
in the Exchange Agreement) and agree to issue the Second Transfer (as defined in
the Exchange Agreement) only after satisfaction of the AMSC Stockholder Approval
(as  defined  in the  Exchange  Agreement).  The  aggregate  number of shares of
American  Mobile Common Stock issuable by American  Mobile in the First Transfer
and the Second  Transfer  would be 8,614,244.  Prior to the Closing,  WorldSpace
would transfer to the Trust all of WorldSpace's right, title and interest in and
to the XM Interest.  After the Closing,  neither  WorldSpace nor the Trust would
have any ownership interest in XM Radio.

We further  understand  that at the Closing,  XM Radio would  recapitalize  (the
"Recapitalization")  its common  stock into two classes - Class A Common  Stock,
having  one vote per  share  (none of which  would be  outstanding)  and Class B
Common Stock,  having three votes per share (the "XM Radio Class B Stock").  The
shares of XM Radio common stock that  American  Mobile  currently  holds and the
shares of XM Radio  common  stock  that  American  Mobile  would  acquire in the
Purchase as part of the XM  Interest  would be  recapitalized  into shares of XM
Radio  Class B Stock in the  Recapitalization  and no other  shares  of XM Radio
Class B Stock would be outstanding. As part of the Recapitalization, pursuant to
the  terms of the  Exchange  Agreement,  American  Mobile  would  return  the XM
Interest  to XM Radio for  cancellation  and XM Radio  would  issue to  American
Mobile a note (the "XM Radio Class B Note")  convertible into  approximately 174
shares  of XM  Radio  Class B Stock  (the  "Exchange").  The XM  Interest  to be
received by American Mobile in the Purchase (as immediately exchanged for the XM
Radio Class B Note in the  Exchange) and the shares of XM Radio Class B Stock to
be  received by American  Mobile in exchange  for its shares of XM Radio  common
stock  in the  Recapitalization  are  referred  to  herein  collectively  as the
"Consideration" to be received by American Mobile.


<PAGE>



We further  understand  that, as more fully  described in the June 5, 1999 draft
Summary of Principal  Terms and  Conditions,  Proposed  Issuance of Subordinated
Convertible  Notes (the "Summary of Principal Terms") and the June 6, 1999 draft
Note Purchase  Agreement by and between XM Radio and the investors named therein
(the  "Note  Purchase  Agreement"),  XM Radio  would  issue at the  Closing in a
private  placement  (the  "Private  Placement")  an aggregate of $250 million of
Series A Subordinated  Convertible Notes to General Motors Corporation,  DIRECTV
(a subsidiary of Hughes Electronics), Columbia Capital, Madison Dearborn, Telcom
Ventures and Clear Channel Communications.

Finally,  we further  understand  that, as more fully  described in the Exchange
Agreement,  at the  Closing,  XM Radio would redeem the Retained XM Interest (as
defined in the Exchange  Agreement)  and pay WorldSpace $75 million in cash (the
"Redemption"). The Purchase, Recapitalization,  Private Placement and Redemption
are contingent on each other and would close concurrently; such transactions are
referred to herein collectively as the "Transaction."

You have asked us to render our  opinion as to whether the  Consideration  to be
received  by American  Mobile in  exchange  for  American  Mobile's  issuance of
American  Mobile  Common  Stock to the Trust in the  Transaction  is fair,  as a
whole, from a financial point of view, to the unaffiliated  public  stockholders
of  American  Mobile.  In that  connection,  we are not  opining as to any other
transactions or arrangements to be entered into or payments to be made, directly
or  indirectly,  by or to  American  Mobile or any  other  person as part of, or
concurrently with, the Transaction.

In the course of our analyses for rendering this opinion, we have:

           1.  reviewed the June 5, 1999 draft Exchange Agreement;

           2.  reviewed the June 5, 1999 draft Summary of Principal Terms;

           3.  reviewed the June 6, 1999 draft Note Purchase Agreement;

           4.  reviewed  the June 4, 1999 draft  Amendment  No. 1 to the Bridge,
               Additional Amounts and Working Capital Loans;

           5.  reviewed  American  Mobile's Annual Reports to  Shareholders  and
               Annual  Reports on Form 10-K for the fiscal years ended  December
               31, 1996 through 1998, and its Quarterly  Report on Form 10-Q for
               the period ended March 31, 1999;

           6.  reviewed certain operating and financial  information,  including
               projections,  provided to us by management of American Mobile and
               XM Radio relating to American Mobile's and XM Radio's  respective
               businesses and prospects;

           7.  met with certain  members of the senior  managements  of American
               Mobile  and  XM  Radio  to  discuss  the  respective  operations,
               historical  financial statements and future prospects of American
               Mobile and XM Radio;

           8.  reviewed the historical prices and trading volume of the American
               Mobile Common Stock;

           9.  reviewed   publicly   available   financial  data,  stock  market
               performance  data and valuation  parameters of a company which we
               deemed generally comparable to XM Radio;

                                        2

<PAGE>



          10.  reviewed the terms of a recent transaction involving the issuance
               of a note convertible into shares of XM Radio common stock; and

          11.  conducted   such   other   studies,   analyses,   inquiries   and
               investigations as we deemed appropriate.

In  the  course  of our  review,  we  have  relied  upon  and  assumed,  without
independent  verification,  the accuracy and  completeness  of the financial and
other information,  including without limitation the projections, provided to us
by American Mobile and XM Radio.  With respect to American Mobile and XM Radio's
projected  financial  results,  we have assumed  that they have been  reasonably
prepared  on  bases  reflecting  the  best  currently  available  estimates  and
judgments of the senior  managements  of American  Mobile and XM Radio as to the
expected future  performance of American Mobile and XM Radio,  respectively.  We
have not assumed any responsibility for the independent verification of any such
information or of the projections provided to us and we have further relied upon
the assurances of the senior  managements  of American  Mobile and XM Radio that
they are  unaware of any facts that would make the  information  or  projections
provided to us incomplete or misleading. In arriving at our opinion, we have not
conducted a physical inspection of any of the properties or assets, and have not
performed or obtained any independent appraisal of the assets or liabilities, of
American  Mobile  and XM  Radio,  nor  have  we been  furnished  with  any  such
appraisals.  Our  opinion is  necessarily  based on  economic,  market and other
conditions,  and the  information  made  available to us, as of the date hereof.
Accordingly, although subsequent developments may affect this opinion, we do not
have any obligation to update, revise or reaffirm this opinion. In rendering our
opinion,   we  have  assumed  that  the  Transaction   will  be  consummated  on
substantially  the  terms  described  in  the  Exchange  Agreement  and  related
documents that we reviewed.

We have been  engaged by  American  Mobile to render  this  fairness  opinion to
American  Mobile in connection  with the Transaction and have received a fee for
such services.  Bear Stearns has been  previously  engaged by American Mobile to
provide certain investment banking and financial advisory services in connection
with American  Mobile's  acquisition of ARDIS Company in 1998 and to act as lead
manager on an offering of senior  notes and  warrants in 1998.  In the  ordinary
course of business,  Bear Stearns may actively  trade the equity  securities  of
American  Mobile for its own account and for the account of its  customers  and,
accordingly, may at any time hold a long or short position in such securities.

Bear Stearns has also acted as exclusive  joint  placement  agent on the Private
Placement  and will  receive  a fee from XM Radio  for such  services.  American
Mobile and XM Radio have expressly  waived any actual or potential  conflicts of
interest  that  might  arise in  connection  with Bear  Stearns'  engagement  by
American  Mobile to render this opinion,  on the one hand, and its engagement by
XM Radio to act as exclusive joint placement agent in the Private Placement,  on
the other hand.

It is  understood  that this letter is intended  for the sole benefit and use of
the  Board  of  Directors  of  American   Mobile  and  does  not   constitute  a
recommendation  to the Board of Directors  of American  Mobile or any holders of
American  Mobile  Common  Stock  as to  how  to  vote  in  connection  with  the
Transaction. This opinion does not address American Mobile's underlying business
decision to pursue the Transaction. This letter is not to be relied upon or used
for any other purpose, or reproduced,  disseminated, quoted to or referred to at
any time,  in whole or in part,  without our prior  written  consent;  provided,
however, that this letter may be included in its entirety in any proxy statement
or other  document to be  distributed  to the holders of American  Mobile Common
Stock in connection with the Transaction.

                                        3

<PAGE>



Based on and subject to the foregoing,  it is our opinion that the Consideration
to be received by American Mobile in exchange for American  Mobile's issuance of
American  Mobile  Common  Stock to the Trust in the  Transaction  is fair,  as a
whole, from a financial point of view, to the unaffiliated  public  stockholders
of American Mobile.



Very truly yours,

BEAR, STEARNS & CO. INC.
By:      /s/Scott Moskowitz
         SENIOR MANAGING DIRECTOR




                                        4

<PAGE>





        This Proxy is Solicited By The Board of Directors of the Company


                      AMERICAN MOBILE SATELLITE CORPORATION


                    PROXY FOR SPECIAL MEETING OF STOCKHOLDERS

                                September 7, 1999


The undersigned hereby constitutes and appoints Walter V. Purnell, Jr., Randy S.
Segal and David H. Engvall and each of them,  true and lawful agents and proxies
("Proxies"),  with full power of substitution  and revocation in each, to attend
the Special Meeting of Stockholders of American Mobile Satellite  Corporation to
be held at 9:00 a.m. on Tuesday,  September 7, 1999 at American Mobile Satellite
Corporation,  10802 Parkridge Boulevard,  Reston, Virginia, and any adjournments
thereof,  and thereat to vote all shares of Common  Stock which the  undersigned
would be  entitled to vote if  personally  present  (i) as  designated  upon the
matters set forth on the reverse  side,  and (ii) in their  discretion,  on such
other business as may properly come before the meeting.

This proxy when properly executed will be voted in the manner directed herein by
the undersigned stockholder.






You are encouraged to specify your choices by marking the appropriate boxes, SEE
REVERSE SIDE.

<PAGE>




(REVERSE SIDE)

1.  Issuance of shares of the Company's      FOR         AGAINST       ABSTAIN
     Common Stock to XM Ventures.            |_|           |_|           |_|



2.  Amendment to the Company's               FOR         AGAINST       ABSTAIN
Certificate of Incorporation to              |_|           |_|           |_|
increase the number of shares
of Common Stock authorized for
issuance to 150,000,000.




                                                      CHANGE OF          |_|
                                                      ADDRESS


INSTRUCTIONS:

1. Please sign exactly as name is printed hereon.
2. If shares are held jointly, each holder should sign.
3. If signing as executor or trustee or in similar  fiduciary  capacity,  please
   give full title as such.
4. If a  corporation,  please sign full  corporate  name by  President  or other
   authorized officer.
5. If a partnership, please sign partners name by authorized person.




SIGNATURE(S)                                       DATE


<PAGE>



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