AMERICAN MOBILE SATELLITE CORP
S-3/A, 1999-03-30
COMMUNICATIONS SERVICES, NEC
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                           Registration No. 333-71423


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                 Amendment No. 1
                                       to
                                    FORM S-3
             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                               -------------------

                      AMERICAN MOBILE SATELLITE CORPORATION
             (Exact name of registrant as specified in its charter)


                  Delaware                     93-0976127
        (State or other jurisdiction        (I.R.S. Employee 
      of incorporation or organization)   Identification Number)

                              10802 Parkridge Blvd.
                           Reston, Virginia 20191-5416
                                 (703) 758-6000
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

                                   Randy Segal
                         Senior Vice President, General
                              Counsel and Secretary
                      American Mobile Satellite Corporation
                              10802 Parkridge Blvd.
                           Reston, Virginia 20191-5416
                                 (703) 758-6130
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

Approximate  date of commencement  of proposed sale to the public:  From time to
time after the effective date of this Registration Statement.


If the only securities  being registered on this Form are being offered pursuant
to dividend or interest reinvestment plans, please check the following box.

If any of the  securities  being  registered on this Form are to be offered on a
delayed or continuous  basis  pursuant to Rule 415 under the  Securities  Act of
1933 (as defined below),  other than securities  offered only in connection with
dividend or interest reinvestment plans, check the following box.  X
                                                                  ---

If this Form is filed to register additional securities for an offering pursuant
to Rule 462(b) under the Securities Act, please check the following box and list
the  Securities  Act  registration  statement  number of the  earlier  effective
registration statement for the same offering. 

If this Form is a  post-effective  amendment filed pursuant to Rule 462(c) under
the  Securities  Act,  check  the  following  box and  list the  Securities  Act
registration  statement number of the earlier effective  registration  statement
for the same offering.

If delivery  of the  prospectus  is  expected  to be made  pursuant to Rule 434,
please check the following box.


<PAGE>








                         CALCULATION OF REGISTRATION FEE
                         -------------------------------

<TABLE>
<CAPTION>
Title of each class      Amount to be        Proposed              Proposed            Amount of
       of                 registered         maximum               maximum          registration fee
 securities to be                         offering price          aggregate
   registered                                  per                 offering
                                              share                 price
- -----------------------------------------------------------------------------------------------------
<S>                       <C>              <C>                <C>                 <C>
Common Stock,
$0.01 par value per
share (1)                  4,836,746            (2)           $21,958,827(2)           $6,105(2)
=====================     ===========      =============      =================   ==============
</TABLE>


(1)  Represents  shares  of  Common  Stock  that  may be  sold  by  certain
     stockholders of the Company.

(2)  Estimated in accordance  with Rule 457(o) under the  Securities  Act solely
     for the purpose of computing the amount of the  registration  fee, based on
     the  average  of the high and low  price of the  Common  Stock  ($4.54)  as
     reported on the Nasdaq  National  Market on March 23, 1999. A filing fee in
     the aggregate  amount of $13,782 was paid in  connection  with the original
     filing of this Registration  Statement on January 29, 1999 for an aggregate
     of 7,779,291 shares of Common Stock and 335,000 Warrants to purchase Common
     Stock. Thus, this Registration  Statement,  as amended, covers an aggregate
     of 335,000  Warrants to purchase Common Stock,  1,258,759  shares of Common
     Stock to be issued upon exercise of the Warrants and  11,357,278  shares of
     Common Stock that may be sold by certain stockholders of the Company for an
     aggregate fee of $19,887.


The registrant hereby amends this  registration  statement on such date or dates
as may be necessary to delay its effective date until the registrant  shall file
a further amendment which specifically  states that this registration  statement
shall  thereafter  become  effective  in  accordance  with  Section  8(a) of the
Securities Act or until this  registration  statement shall become  effective on
such date as the Securities  and Exchange  Commission,  acting  pursuant to said
Section 8(a), may determine.



================================================================================

                                      -2-


<PAGE>





                                EXPLANATORY NOTE
                                ----------------

     This Registration Statement contains two forms of prospectus: (1) the first
will be used in connection  with offers and sales of Warrants to purchase Common
Stock and the  issuance  of shares of Common  Stock  upon the  exercise  of such
Warrants and (2) the second will be used in connection  with offers and sales of
shares of Common  Stock  held by certain  stockholders.  The  sections  in these
prospectuses  relating to general  statements  about the Company,  as opposed to
statements about the securities covered thereby, are identical.



                                      -3 -


<PAGE>






The  information in this  prospectus is not complete and may be changed.  We may
not sell  these  securities  until the  registration  statement  filed  with the
Securities and Exchange Commission is effective.  The prospectus is not an offer
to  sell  these  securities  and it is not  soliciting  an  offer  to buy  these
securities in any state where the offer or sale is not permitted.



                             Subject to Completion

                              Dated March 31, 1999
                                                                      Prospectus
                      AMERICAN MOBILE SATELLITE CORPORATION

                                335,000 Warrants
                        1,258,759 Shares of Common Stock

     In a private  transaction in March 1998, we issued Warrants to purchase our
common stock.  Under this  prospectus,  we are offering the shares of our common
stock that holders of Warrants may purchase upon  exercising  the  Warrants.  In
addition, the holders of these Warrants who are listed inside may offer and sell
their Warrants under this prospectus.

     Our common stock is quoted on the Nasdaq  National  Market and traded under
the symbol "SKYC."

     Our  principal  executive  offices  are located at 10802  Parkridge  Blvd.,
Reston,Virginia 20191-5416, and our telephone number is (703) 758-6000.

                               ------------------

     See "Risk Factors" beginning on page 5 for a discussion of certain material
factors that you should  consider in connection with an investment in our common
stock. 

                               ------------------

     Neither the  Securities and Exchange  Commission  nor any state  securities
commission has approved or  disapproved  of these  securities or passed upon the
adequacy or accuracy of this prospectus. Any representation to the contrary is a
criminal offense.


     The date of this prospectus is March 31, 1999.







<PAGE>






                                TABLE OF CONTENTS
                                -----------------

                                                                            Page

Prospectus Summary.............................................................2
         The Company...........................................................2
         The Offering..........................................................3
Risk Factors...................................................................5
Use of Proceeds...............................................................16
Selling Warrantholders........................................................16
Plan of Distribution..........................................................20
Description of the Warrants...................................................21
Description of Capital Stock..................................................26
Legal Matters.................................................................28
Experts.......................................................................28
Where You Can Find More Information...........................................28







     This  prospectus  contains and  incorporates  by reference  certain forward
looking  statements  within the  meaning of the  Private  Securities  Litigation
Reform Act of 1995 with respect to our business, financial condition and results
of operations,  including,  without  limitation,  statements  under the captions
"Business" and "Management's  Discussion and Analysis of Financial Condition and
Results of  Operations"  in our  annual and  quarterly  reports.  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.  Factors that may cause actual
results to differ  materially  from those  contemplated  by such forward looking
statements  include,  among others, the factors discussed in the section of this
prospectus entitled "Risk Factors."








<PAGE>





                               PROSPECTUS SUMMARY
                               ------------------

     The  following  summary  is  qualified  in its  entirety  by  the  detailed
information and financial statements,  including the notes thereto, contained or
incorporated by reference in this prospectus.

                                   The Company
                                   -----------

     The  Company  was  incorporated  on May 3,  1988.  At  that  time,  the FCC
determined  that the public  interest  would be best served by granting a mobile
satellite  services  license  to a  consortium  of  all  willing  and  qualified
applicants.  The Company was formed by eight of the initial  applicants for that
license.  The FCC  authorized  us to  construct,  launch,  and  operate a mobile
satellite  services  system  to  provide a full  range of mobile  voice and data
services via satellite to land, air and sea-based  customers.  On April 7, 1995,
we  successfully  launched our first  satellite,  MSAT-2,  from Cape  Canaveral,
Florida.

                                Our service area:
                                -----------------

o The continental United States        o Alaska
o Hawaii                               o Puerto Rico
o The U.S. Virgin Islands              o United States coastal waters
o International waters and airspace    o Any foreign territory where the local
                                         government has authorized the provision
                                         of service


     Our wholly-owned  subsidiary,  AMSC Acquisition Company,  Inc. operates our
mobile  satellite  services.  On  March  31,  1998  we  acquired  (through  AMSC
Acquisition) ARDIS Company,  then a wholly-owned  subsidiary of Motorola,  Inc.,
that owns and  operates  a two-way  wireless  data  communications  network.  We
purchased  ARDIS for  approximately  $50  million in cash and $50 million in our
common stock.  Through the acquisition of ARDIS, we became a nationwide provider
of  wireless  communications  services,  including  data,  dispatch,  and  voice
services. We primarily serve business customers in the United States.

     On October 16, 1997,  our  indirect  subsidiary,  XM  Satellite  Radio Inc.
(formerly American Mobile Radio Corporation), received a license from the FCC to
provide satellite-based Digital Audio Radio Service (DARS) throughout the United
States.  XM Radio bid $89.9 million at auction on April 2, 1997 for the license.
XM Radio has and will continue to be funded by parties other than the Company in
exchange  for debt and  equity  interests  in XM Radio.  Accordingly,  we do not
expect that the  development of this business will have a material impact on our
financial  position,  results  of  operations,  or cash  flows.  XM  Radio is an
indirect subsidiary that we own through our direct subsidiary XM Satellite Radio
Holdings Inc. (formerly AMRC Holdings, Inc.).

                                      -2-

<PAGE>

     As a result of the  combination  of our  satellite-based  business with the
ARDIS  terrestrial-based  business,  we now  offer a broad  range of  end-to-end
wireless  solutions  utilizing a seamless  network  consisting  of the  nation's
largest,  most fully-deployed  terrestrial wireless data network and a satellite
in geosynchronous  orbit. Our satellite-only data communications system provides
data  services  primarily  to  long-haul  trucking  customers.   Our  multi-mode
communications system uses both our terrestria and satellite networks to provide
"least-cost  routing"  for two-way data  communications.  We are able to provide
cost-effective  nationwide  coverage for communications  outside the terrestrial
network  coverage  area by  routing  messages  over the lower  cost  terrestrial
network before  automatically  routing messages over the satellite network.  Our
terrestrial network delivers superior in-building penetration,  completion rates
and response times compared to other wireless data networks through the use of a
single frequency reuse technology.

     In addition to providing  data service,  we offer two forms of mobile voice
communications  service:  nationwide  dispatch  service and satellite  telephone
service.  We are the only  company to offer a nationwide  dispatch  service that
allows  multiple  users  located  anywhere in our service area to share a single
connection for point-to-multipoint communication using push-to-talk handsets. We
market our nationwide  dispatch  service  primarily to field services users with
wide-area fleet  communications  needs. Our satellite telephone service provides
traditional  voice,  fax and data service through  satellite  terminals that are
similar to cellular phones. We market our satellite  telephone service primarily
to maritime users, including both commercial and recreational vessels, and other
targeted market segments such as government, public safety organizations and the
natural resource industries.


                                  The Offering
                                  ------------

Securities Offered.............We  are offering  1,258,759 shares of our  common
                               stock issuable upon the exercise of the Warrants.
                               The holders of these  Warrants also may offer and
                               sell  their  Warrants under  this prospectus.  No
                               fractional  shares of common stock will be issued
                               upon exercise of the  Warrants.  Instead,  at the
                               time  of exercise,  the Company  will  pay to the
                               holder of the  Warrant an amount in cash equal to
                               the current market value of any fractional share.

Expiration of Warrants..........The Warrants will expire on April 1, 2008.

Exercise of Warrants............The  Warrants  became  exercisable  on  June 26,
                                1998.   Each  Warrant  entitles  its  holder  to
                                purchase 3.75749 shares of our  common  stock at
                                an  exercise  price  of  $12.51  per  share.  If
                                certain events  listed  in the warrant agreement
                                dated March 31, 1998  occur, we  may  adjust the
                                number of shares of common stock for  which, and
                                the  price  per  share  at  which,  a Warrant is
                                exercisable.


                                      -3-
   

<PAGE>





Listing or Quotation
of Common Stock.................Our  common  stock  is   traded  on  the  Nasdaq
                                National Market under the symbol "SKYC."

Registration....................The warrant registration rights agreement, dated
                                as  of  March 31, 1998,  requires us to register
                                the  Warrants and the common stock we will issue
                                when  Warrants are exercised. Under the terms of
                                the  warrant  registration  rights agreement, we
                                must  use  our   best  efforts   to   keep  this
                                registration statement continuously effective as
                                follows:

                                o   Duration of effectiveness: until the earlier
                                    of  (1)  the  time  when the transfer of the
                                    Warrants  and  the common stock is no longer
                                    restricted  or  (2)  the  expiration  of the
                                    Warrants.


                                o   Suspensions of effectiveness may occur:
                                    - at  our  option,  up  to  two  times
                                      during any consecutive 365-day period;
                                    - for no more than 45 consecutive days
                                      per suspension; and
                                    - only  in  connection  with  a  possible
                                      acquisition, business combination or other
                                      development affecting the Company if (1)
                                      the Board of Directors reasonably believes
                                      that there is a valid business purpose for
                                      a  suspension  and  (2) provides notice of
                                      its determination to holders of Warrants.

Use of Proceeds.................We  will  not receive any proceeds from the sale
                                of the Warrants. To the extent that any Warrants
                                are  exercised,  we  will  receive  the exercise
                                price for the common stock we issue.


                                      -4-



<PAGE>





                                  RISK FACTORS
                                  ------------

We Have Substantial and Continuing Operating Losses
- ---------------------------------------------------

     We have incurred  significant  operating  losses and negative cash flows in
each year since we began operations.  These losses are due primarily to start-up
costs,  the  costs of  developing  and  building  each  network  and the cost of
developing,  selling and providing our products and services. For the year ended
December 31, 1998, we reported operating losses of approximately  $88.2 million.
For historical  periods prior to our acquisition of ARDIS, we reported operating
losses  of  approximately  $97.4  million  and $120  million  in 1997 and  1996,
respectively.  During these same periods,  ARDIS  reported  operating  losses of
approximately  $17.4  million and $29.2  million.  We expect to continue to make
significant capital outlays for the foreseeable future to fund interest expense,
capital  expenditures  and working capital before we begin to generate  positive
cash flow from  operations.  These  outlays are  expected  to  continue  for the
foreseeable future thereafter.  We cannot guarantee that we will have sufficient
resources to complete the expenditures required to operate the business.

     Since inception, we have been engaged in operating our business, recruiting
key  management  and  technical  personnel  and  raising  capital  to  fund  our
operations and the  development of our networks.  We launched  commercial  voice
service in January  1996.  Accordingly,  you only can evaluate our  prospects in
each of our markets based on this short operating history. You must consider the
prospects for our success in light of the risks, expenses and difficulties often
encountered  when  establishing  a new business in an evolving  industry that is
subject  to rapid  technological  and price  changes,  and  characterized  by an
increasing number of market competitors.

     We estimate that we will not have  sufficient  operating  revenues to cover
operating expenses for the foreseeable  future. Our ability to generate positive
operating  cash flow will depend  upon,  among  other  factors,  the  successful
integration of ARDIS into our operations,  the  achievement of related  business
synergies and the successful marketing of our services. We cannot guarantee that
the ARDIS integration,  the achievement of related business  strategies,  or our
marketing efforts will be successful.

     In addition, we will require additional capital for expenditures  necessary
to further develop our business and expand our networks.

We Are Highly Leveraged
- -----------------------

     As of December  31,  1998,  our  indebtedness  totaled  approximately  $486
million ($478 million net of debt discount).  As of December 31, 1998 we had $68
million  available  under AMSC  Acquisition  Company,  Inc.'s  revolving  credit
facility.  ARDIS  received a commitment  from  Motorola for up to $10 million of
vendor financing for certain capital  expenditures.  On a pro forma basis, after
giving effect to the acquisition of ARDIS and the related  financing as if these
transactions  had been  consummated  on January 1 of the period  presented,  our
earnings   would  have  been   insufficient   to  cover  our  fixed  charges  by
approximately  $176.2  million for fiscal  1997 and $151.6  million for the year
ended  December 31, 1998.  At December 31, 1998 our  stockholders'  equity was a
deficit  of  approximately  $24.4  million.  We and  our  subsidiaries  will  be
permitted to incur additional indebtedness in the future.

                                      -5-
<PAGE>

     Beginning April 1, 2001, AMSC  Acquisition,  our  wholly-owned  subsidiary,
will be allowed to pay dividends to us. This will permit us to meet our interest
expenses with respect to our $100 million term loan facility.  Historically,  we
have not generated sufficient earnings or cash flow from operations to make such
interest payments.

     The degree to which we are leveraged  could have important  consequences to
the success of our business including, but not limited to:

     o    increasing our  vulnerability to general adverse economic and industry
          conditions;

     o    limiting  our ability to obtain  additional  financing  to fund future
          working capital,  capital  expenditures,  research and development and
          other general corporate requirements;

     o    requiring the  dedication  of a  substantial  portion of our cash flow
          from  operations  to the payment of principal of, and interest on, our
          indebtedness,  thereby  reducing the availability of such cash flow to
          fund working capital,  capital expenditures,  research and development
          or for other general corporate purposes;

     o    limiting our  flexibility  in planning for, or reacting to, changes in
          our business and the industry; and

     o    placing us at a  competitive  disadvantage  vis-a-vis  less  leveraged
          competitors.

We May Need Additional Capital
- ------------------------------

     We expect to  continue  to make  significant  outlays  for the  foreseeable
future to fund debt service, capital expenditures and working capital. This will
continue until we begin to generate  positive cash flow from  operations and for
the foreseeable  future  thereafter.  If our cash flows from operations are less
than projected,  we will require  additional debt or equity financing in amounts
that could be substantial. The type, timing and terms of financing we may select
will depend upon our cash needs the availability of other financing  sources and
the prevailing  conditions in the financial markets. We cannot guarantee that we
will be able to find any such sources at any given time on favorable terms.

     Motorola  has entered  into an agreement  with our  wholly-owned,  indirect
subsidiary,  ARDIS, to provide up to $10 million of vendor financing, which will
be available to finance up to 75% of the purchase  price of  additional  network
base stations necessary to meet the build-out requirements under a contract AMSC
Acquisition has with the United Parcel  Service.  Funds borrowed under this loan
agreement  have an  interest  rate  equal  to  LIBOR  plus  7% and  the  loan is
guaranteed by us and each subsidiary of AMSC Acquisition.  The terms of the loan
require that amounts  borrowed be secured by the  equipment  purchased  with the
loan. As of December 31, 1998, we had borrowed $1.6 million from Motorola  under
this loan.

   
                                   -6-
<PAGE>
     We  cannot  guarantee  that  our  current  projection  of  cash  flow  from
operations will be accurate.  Our  projections  will depend upon numerous future
factors and  conditions,  many of which are outside of our  control.  You should
note that  projections  are  merely  estimates  of future  events and you should
expect actual events to vary from current  estimates,  possibly  materially.  In
addition,  if  customer  demand  exceeds  our  current  expectations  and we can
accommodate such demand without  adversely  affecting th quality of our service,
we are likely to attempt to accelerate our expansion.  If we elect to accelerate
our  build-out or introduce  new  products or services,  our funding  needs will
increase,  possibly to a significant degree. We cannot guarantee that we will be
able to secure any additional  financing on commercially  reasonable terms or at
all. Our cost of expanding our network and  operating  our business,  as well as
our revenues, will depend on a variety of factors including:

     o    our ability to meet our expansion schedules;

     o    the number of customers and the services for which they subscribe;

     o    the nature and penetration of new services that we and our competitors
          may offer;

     o    regulatory changes; and

     o    changes in technology.

As a result,  our actual  costs and  revenues  may vary from  expected  amounts,
possibly to a material  degree.  Such variations are likely to affect our future
capital  requirements.  Accordingly,  it is possible that we will be required to
raise  substantial  additional  capital  in  the  future  or  that  our  current
projections will prove to be inaccurate.

Our Market Is Rapidly Changing
- ------------------------------

         The markets for wireless  communications  services change rapidly.  Our
success  depends,  in part, on our ability to respond and adapt to such changes.
We cannot guarantee that we will be able to compete effectively under, or adjust
our contemplated  plan of development to meet,  changing market  conditions.  We
cannot  guarantee  that we will be able to  implement  our  strategy or that our
strategy will be successful in this rapidly evolving market.

         This  market  is also  marked  by the  continuous  introduction  of new
products and services and  increased  capacity for services  similar to those we
provide.  Future technological advances in the wireless  communications industry
may  result in the  availability  of new  products  or  services.  Advances  may
increase  the  efficiency  of existing  products or  services.  If a  technology
becomes available that is more  cost-effective or creates a superior product, we
may be unable to access  such  technology  or financ the  necessary  substantial
capital  expenditures that may be required.  Our technology may be rendered less
profitable  or  less  viable  by  existing,   proposed  or  as  yet  undeveloped
technologies.  We cannot guarantee that we will have available the financial and
other  resources  to  compete  effectively  against  companies  possessing  such
technologies.  We are  unable  to  predict  which  of the many  possible  future
products  and  services  will meet  evolving  industry  standards  and  consumer
demands.  We cannot guarantee tha we can adapt to such technological  changes or
offer such  products or services on a timely  basis or  establish  or maintain a
competitive position.

                                      -7-

<PAGE>

We Depend on Market Acceptance
- ------------------------------

     Our success is subject to a number of business,  economic,  regulatory  and
competitive factors, many of which are beyond our control,  including the extent
to which prospective  customers will purchase our services.  The vitality of our
business is subject to the  successful  implementation  of our growth  strategy,
which, in turn, depends,  among other things, on our expectation that demand for
our services will increase  significantly  in the markets we serve.  We have not
yet  commercially  introduced  certain of these services and we cannot guarantee
that any of them will achieve  market  acceptance or result in the generation of
operating  cash flow.  Failure to gain market  acceptance for current or planned
products and services would have a material  adverse effect on our business.  In
addition,  we have  incurred and will  continue to incur  significant  operating
expenses.

     Based upon certain expectations as to the anticipated market acceptance of,
and customer demand for, our services,  we have made, and will continue to make,
significant capital investments. Based on similar expectations, our subsidiaries
have entered into  operating  leases,  equipment  supply  contracts  and service
arrangements, and are attempting to secure financing.  Accordingly, any material
miscalculation  with respect to our  operating  strategy or business  plan could
have a material adverse effect on our business.

We Must Effectively Manage Our Growth
- -------------------------------------

     In our continuing efforts to respond to changing market conditions,  we may
experience periods of rapid expansion.  In order to manage growth effectively in
the  complex  environment  in which we  operate,  we will need to  maintain  and
improve our  operating and  financial  systems and expand,  train and manage our
employee  base.  We must  expand the  capacity  of our sales,  distribution  and
installation  networks in order to achieve  continued growth in our existing and
future markets.  In general, if we fail to manage growth effectively there could
be a material adverse effect on our business, financial condition and results of
operations.

Our Customers Are Highly Concentrated
- -------------------------------------


     After  accounting for the acquisition of ARDIS,  five customers  (including
IBM) accounted for an aggregate of 40% of our service revenue for the year ended
December 31,  1998.  The loss of one or more of these  customers,  or any event,
occurrence or development  which adversely  affects our relationship with one or
more of these customers could have a material adverse effect on our business.


                                      -8-


<PAGE>





We Rely on Third Party Vendors
- ------------------------------

     We  rely  on  independent  vendors  to  develop  and  manufacture  wireless
communications  devices for our networks,  which are significant elements of our
business  plan.  These  suppliers do not sell such devices to us on an exclusive
basis.  We carry a limited  inventory  of such  devices  and  generally  have no
guaranteed  supply  arrangements.   From  time  to  time,  we  have  experienced
interruptions  and/or  delays of supply.  We cannot  guarantee  that we will not
experience such  interruptions  in the future.  In addition,  we have short-term
contracts  with the  majority of our  suppliers.  We cannot  guarantee  that our
suppliers will continue to provide  products to us at attractive  prices,  or at
all, or that we will be able to obtain such products in the future from these or
other providers on the scale and within the time frames we require.  Some or all
of our suppliers could enter into exclusive  arrangements  with our competitors,
or cease selling these components to us at commercially reasonable prices, or at
all. If we fail to obtain such products on a timely basis at an affordable cost,
or experience any significant  delays or interruptions  of supply,  our business
would be materially adversely affected.

     As part of our growth strategy, we rely on our suppliers to reduce the cost
of  wireless  communications  devices  approved  and  available  for  use on our
network.  Our  management  believes  that  reductions  in the  cost of  wireless
communications  devices  will result in increased  sales of devices,  additional
subscribers  for  our  services  and a  corresponding  increase  in our  service
revenues.  If we fail to  obtain  such cost  reductions  on a timely  basis,  or
experience  any  significant  delays of such  reductions,  our business would be
materially adversely affected.

     We expect the anticipated expansion of our operations and infrastructure to
place a  significant  demand  on our  suppliers,  some  of  which  have  limited
resources and production capacity. In addition,  some of our suppliers, in turn,
rely on sole or  limited  sources  of supply for  components  included  in their
products.  If our suppliers fail to adjust to meet such increasing demand,  they
may be unable to supply  devices in the  quantities  and the  quality and at the
times we require, or at all. If we are unable to obtain sufficient quantities of
sole or  limited  source  devices or to develop  alternative  sources,  we could
experience  delays and increased  costs in the expansion of our  operations  and
infrastructure  or become  unable to properly  maintain  our  existing  level of
operations.  Such  occurrences  could  have a  material  adverse  effect  on our
business, financial condition and results of operations.

The ARDIS Technology Is Subject to Competitive Risks
- ----------------------------------------------------

     The ARDIS network, and certain of its competitive  strengths,  such as deep
in-building   penetration,   is  based  upon  a  single  frequency  reuse  (SFR)
technology.  Motorola  holds  the  patent  for SFR  technology  and  ARDIS has a
non-exclusive  license to use the SFR  technology.  ARDIS also relies on support
agreements  with Motorola for support of the  operations of certain  portions of
the ARDIS  network.  However,  Motorola could enter into  arrangements  with our
competitors  and it is  possible  that such  agreements  could  have a  material
adverse effect on us. 

                                      -9-

<PAGE>

There Are Risks Associated With Satellite Technology
- ----------------------------------------------------

     We have an  agreement  with TMI, the Canadian  mobile  satellite  owner and
operator of MSAT-1,  for backup,  restoral and additional  capacity usage if our
satellite fails or we need  additional  capacity.  In return,  we have agreed to
provide TMI with similar  backup  service on our MSAT-2  satellite.  Each of the
MSAT-1 and MSAT-2  satellites  has in the past  experienced  some  technological
malfunctions.  While  recent  MSAT-2  malfunctions  have  involved  either spare
components or ones that did not have a material impact on current operations, it
is possible that either or both satellites could experience future  malfunctions
at any time.

     MSAT-2 has an expected  end of service  life of 2006,  subject to potential
technological  failures  and other  factors.  For  example,  random  failure  of
satellite  components  could  result in damage to or loss of MSAT-2.  It is also
possible that the  satellite  could be damaged by  electromagnetic  storms or
collisions with other objects,  although such occurrences are rare. Although the
actual service life of the satellite may exceed its expected service life,
we cannot  guarantee that the expected  service life of the satellite will be
achieved or  exceeded.  Although  we have  in-orbit  insurance  for a failure of
MSAT-2,  it is  unlikely  that any  recovery  under such  insurance  would fully
compensate us for losses we would sustain from such a failure. In addition,  the
in-orbit  insurance  policy is subject  to annual or  biannual  renewal,  and we
cannot   guarantee  that  insurance  on  favorable  terms  and  at  commercially
reasonable rates will remain available for coverage of MSAT-2.


Our Remote Disaster  Recovery System for the Satellite Network Ground Segment Is
- --------------------------------------------------------------------------------
Limited
- -------

     Presently,  our disaster recovery systems focus on internal  redundancy and
diverse  routing  within  each of the  facilities  operated  by or for  us.  For
example,   the  ARDIS  terrestrial   network  has  access  to  a  remote  ground
communications  backup complex that would enable us to continue to provide ARDIS
services in the event of a natural disaster affecting one geographic site. We do
not,  however,  currently  have  access  to a  remote  backup  satellite  ground
communications  facility  that would  enable us to  continue  to process  mobile
satellite  communications  services  for  customers  in the  event of a  natural
disaster or other occurrence that rendered the system unavailable.  Our business
is subject to the risk that such a disaster or other  occurrence could hinder or
prevent  us from  continuing  to  provide  some  services  to some or all of our
customers.

Our Industry Is Highly Competitive
- ----------------------------------

     The  wireless   communications   industry  is  highly  competitive  and  is
characterized by frequent technological innovation.  The industry includes major
domestic and international companies,  many of which have financial,  technical,
marketing,  sales,  distribution and other resources  substantially greater than
ours and which  provide,  or plan to provide,  a wider range of services than we
will provide.  Our products and services compete with a number of communications
services,  including  existing  satellite  services,  terrestrial  air-to-ground

                                      -10-

<PAGE>


services,  and terrestrial  land-mobile and fixed services, and may compete with
new  technologies  in the future.  In addition,  the FCC has recently  allocated
large amounts of additional  spectrum for communications  uses or potential uses
that could compete with us. Additional allocations of spectrum for such uses may
occur in the future.

Our Business Is Subject to Regulatory Risks
- -------------------------------------------

     The ownership and  operations of our  communication  systems are subject to
significant  regulation by the Federal Communications  Commission.  The FCC acts
under  authority  granted by the  Communications  Act of 1934,  as amended,  and
related  federal  laws.  A number of our  licenses are subject to renewal by the
FCC.  Our  satellite   operations   are  subject  to   international   frequency
coordination.  Current FCC regulations generally limit the ownership and control
of our company by  non-U.S.  citizens or entities to no more than 25%. We cannot
guarantee that the rules and regulations of the FCC will continue to support our
operations as we presently  conduct them and plan to conduct them in the future.
We cannot  guarantee  that all existing  licenses  will be renewed and requisite
frequencies coordinated.

     There are  applications  by others  now  pending  before the FCC to use the
Inmarsat system and TMI's Canadian-licensed system, both of which operate in the
MSS L-band and have satellite  footprints covering the United States, to provide
service in the United  States.  We have opposed  these  filings.  In addition to
providing additional competition to us, a grant of domestic authority by the FCC
to use any of these foreign systems may increase the demand by these systems for
spectrum in the  international  coordination  process and could adversely affect
our ability to coordinate our spectrum access.

     On July 20,  1998,  the FCC granted  SatCom a Special  Temporary  Authority
(STA) to operate up to 500 mobile  terminals  for 180 days on a private  carrier
basis  so  that it may  conduct  marketing  trials;  this  STA was  subsequently
extended to July 12, 1999. On July 30, 1998, we filed an Application  for Review
and a Motion for Stay of this Special  Temporary  Authority  grant with the FCC,
and these filings remain pending.  

Our Business Is Subject to the Year 2000 Problem
- ------------------------------------------------

     We have developed and are  implementing  a Year 2000  Readiness  Program to
address Year 2000 issues.  "Year 2000  Ready," or "Year 2000  Readiness,"  means
that  customers  will  experience  no material  difference  in  performance  and
functionality of our networks prior to, during or after the year 2000.

     Our Year 2000 Readiness  Program uses the phased  approach that is standard
in our  industry.  The  Awareness,  Inventory  and  Assessment  phases have been
completed,  and we are at various stages of the Renovation,  Validation/Test and
Implementation/Rollout phases, depending on the particular system involved.


                                      -11-

<PAGE>


     The  Inventory  and  Assessment  Phases  concentrated  on our core business
systems:  those systems, both hardware and software,  whose failure could have a
material  impact on our financial  condition and operations.  Vendors  providing
critical  products and services to us are also  included in this  definition  of
core business  systems.  Although the core business systems are the top priority
in our Year 2000 Readiness Program, we assessed all of our software and hardware
for Year 2000 Readiness.

     Our plans for the Renovation,  Validation/Test  and  Implementation/Rollout
Phases  call for us to be Year  2000  Ready by the end of the third  quarter  of
1999.  In  addition,   we  are  currently  scheduled  to  complete   renovation,
implementation and rollout of our internal systems (including our voice customer
billing  software,  CMIS) in the fourth quarter 1999;  these  internal  software
systems do not affect our ability to pass customer  traffic and  therefore  will
not affect Year 2000 Readiness. While there can be no assurances that we will be
successful  or that we will  complete  the Year 2000  Readiness  Program by that
time,  we  believe  we will  have  sufficient  time to make  our  core  systems,
including internal systems, Year 2000 Ready before December 31, 1999.

     The  complex  of  hardware  and  software  that  we  maintain  consists  of
commercial  off-the-shelf (COTS) software,  as well as custom software developed
specifically  for our networks.  In certain cases,  American  Mobile's Year 2000
Readiness  Program  involves  upgrading COTS software that is unsupported by the
vendor or whose Year 2000 Readiness could not be determined. Upgrading such COTS
software,  as  planned,  provides  greater  certainty  regarding  the Year  2000
Readiness of such products and ensures that vendor suppor will be available.

     The total cost of our Year 2000 Readiness  Program was  approximately  $2.4
million in 1998.  Expenditures  for the Year 2000 Readiness  Program in 1999 are
estimated to be up to $7.4  million.  Some  modification  costs,  including  the
purchase of software upgrades and consulting services,  are expensed as incurred
while other modification costs, such as hardware purchases, are being treated as
capital expenditures.

     The  estimated  cost and date on which we believe our network  will be Year
2000  Ready are  based on  management's  best  estimates.  However,  there is no
guarantee  that we will achieve  these  results and actual  results could differ
materially from those anticipated.  Nevertheless,  it is difficult or impossible
to foresee all the risks  associated  with  making our network  Year 2000 Ready.
Some of our critical business systems depend  significantly on software programs
and third party services that are not within our control.  Failure to solve Year
2000  errors  within our  critical  business  systems  could  result in possible
service outages,  miscalculations  or disruption of operations that could have a
material  impact on our business.  Our Year 2000  Readiness  Program may fail to
foresee  some risks or may not  address  them  adequately.  Because of our heavy
dependence  on  software,  some  Year  2000  problems  may not be  found  or the
remediation  efforts may introduce new bugs that are not identified  before they
impact operations. This applies to both COTS software and custom software.

                                      -12-

<PAGE>


     If our  customers  fail to become  Year 2000  ready on time with  their own
hardware and software systems,  their  applications may not function even if our
systems are Year 2000 Ready.  This will result in reduced  traffic and revenues.
Also, suppliers of goods and services may suffer Year 2000-related failures from
which we cannot adequately protect our business.

     While  management  believes  that we will be  able  to  achieve  Year  2000
Readiness in a timely manner,  the schedule for completing the implementation of
several core business  systems extends to the fourth quarter 1999 and there is a
possibility  that we may not become  Year 2000  Ready on time or within  budget.
Contingency  planning, as discussed below, is currently underway to minimize the
risk of  business  interruptions  caused by Year 2000  problems  within the core
business systems.

     We have contingency plans in place to minimize service  interruptions  that
can mitigate, although not eliminate, interruptions caused by problems resulting
from Year 2000 issues. For example, we have backup power supplies and generators
in place for certain  portions of our networks in the event of electrical  power
outages.  In addition,  for some services we have  contracted with more than one
service provider.  These plans, systems and services are being incorporated into
our Year  2000  contingency  planning.  To the  extent  that it is  commercially
reasonable to do so, we will include other  redundant or alternative  sources of
services in our Year 2000 contingency  planning  efforts.  We anticipate  having
additional Year 2000 contingency plans in place by June 1999.

Five Principal Stockholders Control the Company
- -----------------------------------------------

     Our principal  stockholders are Hughes  Communications  Satellite Services,
Inc., Motorola, Inc., Baron Capital, Inc., Singapore Telecommunications Ltd. and
AT&T Wireless Services,  Inc. These stockholders hold in aggregate approximately
75.7% of our  common  stock  on a fully  diluted  basis.  We have  entered  into
material  contracts and  transactions  with our principal  stockholders or their
affiliates  and we may enter into  additional  contracts  in the  future.  These
contracts may include the guarantee of our debt obligations.  These stockholders
have other interests in the  communications  industry that may conflict with our
interests.

We Are Dependent on Our Key Personnel
- -------------------------------------

     We are dependent on the efforts of a group of employees  with technical and
business knowledge regarding our systems. If we lose the services of one or more
of these  individuals it could  materially and adversely affect our business and
our future  prospects.  We do not maintain key man life  insurance on any of our
officers or  employees.  Our future  success  will also depend on our ability to
attract and retain  additional  management and technical  personnel  required in
connection with the growth and development of our business. If we fail to retain

                                      -13-

<PAGE>


or attract such key personnel  there could be a material  adverse  impact on our
business, financial condition and results of operations.

Our Charter and Bylaws Contain Anti-takeover Provisions

     Our  Certificate  of  Incorporation  and  Bylaws and the  Delaware  General
Corporation Law contain provisions that may have the following effects:

     o    discouraging,  delaying or making more  difficult a change in control;
          and

     o    preventing the removal of incumbent directors.

     The existence of these provisions may negatively impact on the price of our
common stock and may discourage  third-party  bids.  These provisions may reduce
any premiums paid to stockholders  for their common stock.  Furthermore,  we are
subject to Section 203 of the  Delaware  General  Corporation  Law.  Section 203
governs business combinations with interested stockholders,  and also could have
the effect of delaying or preventing a change in control.

     Our  Certificate  of  Incorporation  also allows our Board of  Directors to
issue up to 200,000 shares of preferred stock and to fix the rights,  privileges
and  preferences  of such  shares  without  any  further  vote or  action by the
stockholders. If this preferred stock is issued in the future, the rights of the
holders may adversely affect the rights of the holders of common stock. While we
have no present  intention to issue shares of preferred stock, any such issuance
could be used to discourage, dela or make more difficult a change in control.

We Have Not Paid Dividends
- --------------------------

     We have not  declared or paid any  dividends  on our common stock since our
date of  inception.  We intend to retain any  earnings to support the growth and
development of our business and we have no present intention of paying dividends
in the  foreseeable  future.  In  addition,  our  ability  to pay  dividends  is
restricted by agreements we have made with several banks in connection  with our
loans and credit facility arrangements.

The Prices of Our Common Stock and Warrants Could Be Volatile
- -------------------------------------------------------------

     Historically, the market prices for securities of emerging companies in the
telecommunications  industry  have been highly  volatile.  Future  announcements
concerning our business or the business of our competitors, including results of
technological  innovations,  new commercial products, or government  regulations
may have a  significant  impact on the  market  price of our common  stock.  Our
common stock has been thinly  traded since our initial  public  offering and its
price has been highly volatile in recent periods.

We Have Shares Eligible for Future Sales
- ----------------------------------------

     Future sales of substantial  amounts of our common stock, or the perception
that such sales may occur,  could adversely affect the value of the common stock

                                      -14-

<PAGE>


and could impair our ability to raise  additional  capital in the future through
the sale of equity securities. As of February 26, 1999, we had 32,237,078 shares
of common  stock  outstanding.  Of these  shares,  22,569,311  shares are freely
tradeable in the open market without  restriction or further  registration under
the Securities Act. The remaining  9,667,767  shares of common stock are subject
to various  registration  rights agreements,  lock-up agreements and shareholder
agreements.  In  addition,  if the  Warrantholders  and  certain  of  our  other
stockholders  exercise  their  warrants,  we will have an  additional  2,071,259
shares of common stock  outstanding,  all of which will be freely tradeable.  We
also have  10,215,721  shares of  common  stock  subject  to other  warrants  or
reserved for issuance to certain stockholders and under certain employee benefit
and stock incentive  plans, all of which are registered for resale or subject to
various  registration  rights  agreements,  lock-up  agreements and  shareholder
agreements. See "Description of Capital Stock."

There is Not a Public Market for the Warrants
- ---------------------------------------------

     There is no public  market for the  Warrants  and we do not intend to apply
for listing of the Warrants on any securities exchange or on the Nasdaq National
Market.

     We cannot guarantee that a liquid market for the Warrants will develop.  If
an active  market  does not  develop,  the  market  price and  liquidity  of the
Warrants may be adversely affected.  Historically,  the market for Warrants such
as those  offered  hereby  has been  subject  to  disruptions  that have  caused
substantial volatility in the prices of similar securities.  We cannot guarantee
that, if a market for the Warrants  were to develop,  such a market would not be
subject to similar disruptions.  Any such disruptions may have an adverse effect
on the holders of the Warrants.


                                      -15-



<PAGE>



                                 USE OF PROCEEDS
                                 ---------------

     We will not  receive  any  proceeds  from the sale of the  Warrants  by the
holders. To the extent that any holder exercises  Warrants,  we will receive the
exercise  price  for the  common  stock we issue  upon  the  exercise,  which is
currently  $12.51 per share.  We will use any  proceeds  we receive  for general
corporate  purposes.  However,  we cannot  guarantee  that any Warrants  will be
exercised.

                             SELLING WARRANTHOLDERS
                             ----------------------

     We  originally  issued  and sold the  Warrants  in March 1998 as part of an
offering of 335,000 units.  As part of this offering,  we entered into a warrant
agreement, dated as of March 31, 1998, with our warrant agent, State Street Bank
and Trust Co. Each unit consisted of $1,000  principal amount of 12 1/4 % Senior
Notes due 2008 of AMSC Acquisition Company, Inc. and one Warrant. The units were
offered to Bear Stearns & Co. Inc., J.P. Morgan & Co., TD Securities  (USA) Inc.
and BancAmerica Robertson Stephens in a private placement. The units were resold
by these  initial  purchasers  in  transactions  exempt  from  the  registration
requirements  of the  Securities  Act of 1933.  Within  the United  States,  the
initial purchasers sold Warrants to qualified  institutional  buyers (as defined
in Rule 144A under the  Securities  Act).  Outside the United States the initial
purchasers  sold  Warrants  to  non-U.S.  persons in  offshore  transactions  in
reliance on Regulation S under the Securities Act.

     The   following   table  shows,   as  of  March  22,  1999,   each  Selling
Warrantholder,  the  number of  Warrants  and  shares of common  stock that each
holder  beneficially  owned and the number of Warrants each is offering pursuant
to this  prospectus.  However,  we cannot  provide  you with an  estimate of the
number of  Warrants or shares of common  stock that the  Selling  Warrantholders
will hold in the future.  This  information is  unavailable  because the Selling
Warrantholders may sell all, some or none of the Warrants they own and may elect
to exercise or hold their Warrants.

     Except as shown in the table,  none of the Selling  Warrantholders  has, or
within  the  past  three  years  has  had,  any  position,  office  or  material
relationship  with us or any of our  predecessors  or affiliates.  The table has
been  prepared  based upon  information  furnished  to us by or on behalf of the
Selling Warrantholders.


                                      -16-


<PAGE>







                        Number of Warrants Being Offered
                        --------------------------------

<TABLE>
<CAPTION>
                                                                                                Number of
                                                                                              Warrants Being
                                 Securities Beneficially Owned Prior to Offering (1)             Offered
                                 ---------------------------------------------------             -------


       Name of Selling         Number of              Number
        Warrantholder          Warrants              of Shares            Percent (2)              Number
        -------------          --------              ---------            -----------              ------

<S>                             <C>                    <C>                  <C>                   <C>  
American Express Trust           3,500(3)               13,151              *                      3,500
Company

The Bank of New York (4)        34,541                 129,787              0.403                 34,541

Bankers Trust Company           35,200                 132,263              0.410                 35,200

Bear, Stearns Securities        27,865(6)              104,702              0.325                 27,865
Corp. (5)

Boston Safe Deposit and          7,900                  29,684              *                      7,900
Trust Company

Brown Brothers Harriman &        9,875                  37,105              0.115                  9,875
Co.

Chase Bank of                    4,000                  15,029              *                      4,000
Texas, N.A.(7) 

Chase Manhattan Bank(7)         49,755                 186,953              0.580                 49,755

Chase Manhattan                  4,875                  18,317              *                      4,875
Bank/MSTC(7) 

Chase Manhattan Bank(7)            365                   1,371              *                        365

Citibank, N.A.(7)                5,540                  20,816              *                      5,540

Custodial Trust Company            500                   1,878              *                        500
 
Deltec Asset Management            564                   2,119              *                        564
Corporation

The Fifth Third Bank               745                   2,799              *                        745

First Marathon Securities        9,000                  33,187              0.103                  9,000
Limited

First Union National Bank          500                   1,878              *                        500

Goldman, Sachs & Co.               250                     939              *                        250

Ing Baring Furman Selz LLC      12,850                  48,283              0.150                 12,850

Investors Bank &                19,450                  73,083              0.227                 19,450
Trust/M.F. Custody


</TABLE>



                                     - 17 -


<PAGE>


<TABLE>
<CAPTION>
                                                                                                Number of
                                                                                              Warrants Being
                                 Securities Beneficially Owned Prior to Offering (1)             Offered
                                 ---------------------------------------------------             -------



       Name of Selling          Number of              Number
        Warrantholder           Warrants              of Shares            Percent (2)              Number
        -------------           --------              ---------            -----------              ------

<S>                             <C>                     <C>                 <C>                   <C>   
Investors Fiduciary Trust        4,350                  16,345              *                      4,350
Company

Lehman Brothers, Inc.            1,400                   5,260              *                      1,400

Mercantile-Safe Deposit &          250                     939              *                        250
Trust Company

NationsBanc Montgomery           5,600                  21,041              *                      5,600
Securities LLC(7) 

The Northern Trust                 440                   1,653              *                        440
Company

PNC Bank, National               2,660                   9,994              *                      2,660
Association

Prudential Securities            2,000                   7,514              *                      2,000
Incorporated

SG Cowen Securities Corp.        1,250                   4,696              *                      1,250

SG Cowen Securities                175                     657              *                        175
Corp./Custody

Spear, Leeds & Kellogg             250                     939              *                        250

SSB - Trust Custody              5,000                  18,787              *                      5,000

State Street Bank and Trust     72,600                 272,793              0.846                 72,600
Company(8) 

Star Bank, National              1,000                   3,757              *                      1,000
Association, Cincinnati

U.S. Bank National               8,000(9)               30,059              *                      8,000
Association

Yasuda Bank and Trust            2,500                   9,393              *                      2,500
Company (U.S.A.)

</TABLE>

- ------------
*Less than 0.1%
(1)      Reflects  beneficial  ownership  of Warrants and shares of common stock
         prior to giving effect to the sale by the Selling Warrantholders of the
         Warrants or the exercise of the Warrants.

                                     - 18 -


<PAGE>




(2)      Reflects  the  percentage  of the  outstanding  shares of common  stock
         beneficially owned by the Selling Warrantholders.
(3)      Includes  2,000 warrants  beneficially  owned by IDS Life Managed Fund,
         Inc. and 1,500 warrants beneficially owned by IDS Life Income Advantage
         Fund.
(4)      This Selling Warrantholder has provided two letters of credit on behalf
         of Baron Capital,  Inc. that were issued in support of Baron  Capital's
         guarantee  of our term loan and  revolving  credit  facilities,  for an
         aggregate amount of $25 million.
(5)      Bear,  Stearns & Co. Inc., an affiliate of this Selling  Warrantholder,
         has  provided   investment   advisory   services  to  us  and  to  AMSC
         Acquisition,  and served as the managing underwriter for the March 1998
         offering of 335,000 units, of which the Warrants were a part.
(6)      Includes  340  warrants  beneficially  owned by The  Common  Fund f/a/o
         Absolute Return Fund, 1,310 warrants  beneficially owned by Safe Harbor
         Partners,  L.P.,  2,180  warrants  beneficially  owned  by Safe  Harbor
         Partners  II, L.P.  and 190  warrants  beneficially  owned by Worldwide
         Transactions Ltd.
(7)      Either this  Selling  Warrantholder  or an  affiliate  of this  Selling
         Warrantholder  is a  participant  in the  banking  syndicate  that  has
         provided  funds to us through the  revolving  credit  facility and term
         loan facility.
(8)      This Selling  Warrantholder  has served as a trustee,  exchange  agent,
         unit  agent and  collateral  agent for us and for AMSC  Acquisition  in
         connection  with the March 1998 offering of 335,000 units, of which the
         Warrants were a part.
(9)      These warrants are beneficially owned by High Yield Portfolio.


                                     - 19 -





                              PLAN OF DISTRIBUTION
                              --------------------

Distribution of Warrants
- ------------------------

     The  Selling  Warrantholders  may,  from  time to time,  sell the  Warrants
directly to purchasers. Alternatively, the Selling Warrantholders may, from time
to time, offer to sell the Warrants to or through  underwriters,  broker-dealers
or agents, who may receive  compensation in the form of underwriting  discounts,
concessions or commissions from the Selling  Warrantholders or the purchasers of
Warrants.  The Selling  Warrantholders  and any underwriters,  broker-dealers or
agents that  participate in the distribution of the Warrants may be deemed to be
"underwriters"  within the meaning of the Securities Act. Any profit on the sale
of  Warrants  by them,  and any  discounts,  commissions,  concessions  or other
compensation received by any of them, may be deemed to be underwriting discounts
and commissions under the Securities Act.

     Holders may offer and sell the Warrants under this  prospectus from time to
time in one or  more  transactions.  These  sales  may be at  fixed  prices,  at
prevailing  market prices at the time of sale, at varying  prices  determined at
the  time of sale or at  negotiated  prices.  The  Selling  Warrantholders  will
determine  these  prices  either  alone or by agreement  with  underwriters  and
dealers  who may receive  fees or  commissions  in  connection  with sales.  The
Selling  Warrantholders  may  use  any of the  following  methods  when  selling
Warrants, which may involve crosses or block transactions:

     o    sales on any national  securities  exchange or quotation  service,  if
          any,  on which  the  Warrants  may be  listed or quoted at the time of
          sale;

     o    sales in the over-the-counter market; or

     o    transactions   otherwise   than   on   such   exchanges   or  in   the
          over-the-counter market.

     o    through the writing of options  (whether such options are listed on an
          options  exchange or otherwise) or, on settlement of short sale of the
          Warrants.


     If required,  a prospectus  supplement  will be  distributed  at the time a
particular  offering  of  Warrants is made.  The  supplement  will set forth the
aggregate  amount and type of Warrants  offered  and the terms of the  offering.
Terms listed may include the name or names of any  underwriters,  broker-dealers
or agents, any discounts,  commissions and other terms constituting compensation
from the Selling  Warrantholders  and any discounts,  commissions or concessions
allowed or reallowed or paid to broker- dealers.

Distribution of Common Stock
- ----------------------------

     We  are  offering  our  common  stock  to  the  Selling  Warrantholders  in
connection with the exercise of the Warrants pursuant to the warrant  agreement.
We do not intend that the Selling  Warrantholders  will use this  prospectus  in
connection with resales of this common stock.

                                      -20-




<PAGE>



We Will List the Common Stock But Not the Warrants on Nasdaq
- ------------------------------------------------------------

     Our outstanding  common stock is listed on the Nasdaq National Market,  and
we have  applied  for  listing of the shares of common  stock to be issued  upon
exercise of Warrants on the Nasdaq  National  Market.  We do not intend to apply
for listing of the  Warrants on any  securities  exchange or  authorization  for
quotation of the Warrants on any quotation  system. We cannot guarantee that any
liquid trading market will develop for the Warrants.

We Will Register the Warrants and Common Stock
- ----------------------------------------------

     We have filed the registration  statement, of which this prospectus forms a
part, with the SEC, as required pursuant to the terms of a warrant  registration
rights  agreement,  dated as of March 31, 1998 among the Company and the initial
purchasers of the 335,000  units.  See  "Description  of Warrants - We Must Keep
This Registration Statement Effective."

     The  warrant  registration  rights  agreement  provides  that we  will  pay
expenses  associated with the  registration of the Warrants and the common stock
issued upon exercise of the Warrants,  including, but not limited to, SEC filing
fees. However, the Selling  Warrantholders will pay all underwriting  discounts,
selling  commissions  and transfer taxes, if any. We have agreed with holders of
Warrants and common stock  acquired upon exercise of Warrants to indemnify  each
other against certain  liabilities,  including certain liabilities arising under
the Securities Act.

     To comply with the securities laws of certain jurisdictions, if applicable,
Selling  Warrantholders  will offer or sell Warrants in such  jurisdictions only
through  registered  or licensed  brokers or dealers.  In addition,  the Selling
Warrantholders  will offer or sell Warrants (unless they have been registered or
qualified  for  sale)  only  in  such  jurisdictions  where  an  exemption  from
registration or qualification is available.


                           DESCRIPTION OF THE WARRANTS
                           ---------------------------

     The Warrants were issued pursuant to the warrant  agreement dated March 31,
1998  in a  private  transaction  that  was  not  subject  to  the  registration
requirements of the Securities Act. The following summary of certain  provisions
of the warrant agreement does not purport to be complete and is qualified in its
entirety by reference to the warrant  agreement and the Warrants,  including the
definitions of certain terms in the warrant agreement and the Warrants.

Exercise Price:  $12.51 per share for 3.75749 shares of common stock

     Each  Warrant,  when  exercised  by its holder,  will entitle the holder to
receive 3.75749 fully paid and  non-assessable  shares of our common stock at an
exercise price of $12.51 per share,  subject to  adjustment.  The exercise price
and the number of shares of common stock issuable upon exercise of a Warrant are
both subject to adjustment as described later in this section.

                                      -21-

<PAGE>


Expiration Date: April 1, 2008
- ------------------------------

     The Warrants became  exercisable on June 26, 1998.  Unless  exercised,  the
Warrants will expire on April 1, 2008.  The Warrants  entitle the holders of the
Warrants to purchase,  in the  aggregate,  approximately  3% of our  outstanding
common  stock  on a  fully-diluted  basis  as of the  date  of  issuance  of the
Warrants,  after giving effect to the exercise of all  in-the-money  outstanding
options and rights we have issued.  We will give notice of  expiration  not less
than 90 nor more than 120 days prior to the  expiration  date to the  registered
holders of the then outstanding  Warrants.  If we fail to give this notice,  the
Warrants  will not expire until 90 days after we give  notice.  In no event will
holders  be  entitled  to any  damages or other  remedy for our  failure to give
notice, other than this extension.

Exercise and Payment Procedures
- -------------------------------

     Holders may exercise the Warrants by  surrendering to the warrant agent the
Warrant  certificates  evidencing  the Warrants to be  exercised  along with the
accompanying form of election to purchase,  properly completed and executed, and
the payment of the exercise price.  Holders may choose to pay the exercise price
in the form of cash,  by a certified or official bank check payable to the order
of the Company,  or by surrender of additional  Warrants.  Upon surrender of the
Warrant  certificate  and paymen of the exercise  price,  the warrant agent will
deliver or cause to be  delivered,  to or upon the written  order of the holder,
stock  certificates  representing  the number of whole shares of common stock or
other securities or property to which such holder is entitled under the Warrants
and the warrant agreement.  The warrant agent will also deliver,  if applicable,
any cash payment to adjust for  fractional  shares of common stock issuable upon
the  exercise.  If  less  than  all  of  the  Warrants  evidenced  by a  Warrant
certificate  are  exercised,   the  warrant  agent  will  issue  a  new  Warrant
certificate.

     The warrant  agent's name,  address and  telephone  number are as set forth
below:

         State Street Bank and Trust Company
         Goodwin Square
         225 Asylum Street
         Hartford, Connecticut  06103
         Attention:  Steve Cimalore
         Tel.: 860 244-1844
         Fax.: 860 244-1897

Fractional Shares Will Not Be Issued
- ------------------------------------

     The warrant agent will not issue any fractional shares of common stock upon
exercise of the Warrants.  When the holder exercises the Warrant, we will pay to
the holder an amount in cash equal to the current market value of the fractional
share.

                                      -22-




<PAGE>


Warrant Holders Do Not Have Common Stockholder Rights
- -----------------------------------------------------

     The holders of the Warrants will have no right to vote on matters we submit
to our stockholders and will have no right to receive dividends.  The holders of
Warrants  will  not be  entitled  to  share  in our  assets  in the  event  of a
liquidation,   dissolution   or  winding  up.  In  the  event  a  bankruptcy  or
reorganization  is commenced by or against us, a bankruptcy  court may hold that
unexercised  Warrants are executory  contracts,  subject to rejection by us with
approval  of the  bankruptcy  court.  The  holders  of  Warrants  may,  even  if
sufficient  funds are available,  receive nothing or a lesser amount as a result
of any such bankruptcy case than they would be entitled to if they had exercised
their Warrants prior to the commencement of any such case.

We Must Keep This Registration Statement Effective
- --------------------------------------------------

     The warrant  registration rights agreement dated March 31, 1998 requires us
to use our  best  efforts  to keep the  registration  statement,  of which  this
prospectus is a part,  continuously  effective  until the Warrants expire or, if
earlier, all of the Warrants and common stock we issue upon exercise of Warrants
cease to be "Transfer Restricted Securities." A Warrant or share of common stock
ceases to be a "Transfer  Restricted  Security"  when such Warrant or share,  as
applicable:

     o    has been effectively  registered under the Securities Act and disposed
          of in accordance with the registration statement covering it;

     o    is distributed to the public pursuant to Rule 144; or

     o    may be sold or  transferred  pursuant  to Rule  144(k) (or any similar
          provisions then in force) under the Securities Act or otherwise.

     During any  consecutive  365-day  period,  we are  entitled  to suspend the
effectiveness  of this  registration  statement on two occasions for a period of
not more than 45  consecutive  days,  except for the 45  consecutive-day  period
immediately prior to the expiration of the Warrants, if two factors are present.
First,  there must be a possible  acquisition  or business  combination or other
transaction,  business  development  or  event  involving  us that  may  require
disclosure in this registration  statement.  Second, the Board of Directors must
determine,  in the  exercise  of  its  reasonable  judgment,  that  either  such
disclosure is not in the best interest of the Company and its  stockholders,  or
it would be  impracticable  to obtain any  financial  statements  relating to an
acquisition or business combination required to be included in this registration
statement. However, in no event are we required to disclose the business purpose
for any suspension, if we determine in good faith that the business purpose must
remain confidential.  We cannot guarantee that we will be able to file, cause to
be declared effective,  or keep a registration  statement continuously effective
until all of the Warrants have been exercised or have expired.

     Each  holder  of  Warrants  that  sells  such  Warrants  pursuant  to  this
registration  statement  generally  will be  required  to be named as a  selling
securityholder  in this prospectus and to deliver a prospectus to the purchaser.
Each holder will be subject to certain of the civil liability  provisions  under
the  Securities  Act in connection  with such sales and will be bound by certain

                                      -23-

<PAGE>


provisions of the warrant  registration  rights agreement that are applicable to
such holder (including certain indemnification  obligations).  In addition, each
holder of Warrants and common stock  acquired  upon exercise of Warrants will be
required to deliver  information to be used in connection with this registration
statement in order to have its Warrants and shares of common stock included.

We May Adjust the Exercise Price
- --------------------------------

     The  exercise  price and  number of  shares  of  common  stock  that can be
purchased  by  exercising  Warrants  will be  subject to  adjustment  in certain
events, including:

     o    the payment by the Company of dividends  (or other  distributions)  on
          common stock payable in common stock;

     o    the subdivision, combination or reclassification of common stock;

     o    the  issuance  to all  holders of common  stock of rights,  options or
          warrants  entitling  them  to  subscribe  for  common  stock,  or  for
          securities convertible into or exercisable for shares of common stock,
          in either  case at an  offering  price (or with an initial  conversion
          exchange  or exercise  price) that is less than the Fair Market  Value
          per share of common stock (as defined below);

     o    the  distribution  to all holders of common stock of any of our assets
          (including  cash),  debt securities,  preferred stock or any rights or
          warrants to purchase any such securities  (excluding  those rights and
          warrants referred to in the preceding bullet point);

     o    the issuance of securities convertible into or exchangeable for common
          stock for a conversion or exchange price plus  consideration  received
          upon issuance less than the then Fair Market Value per share of common
          stock (excluding  securities issued in transactions referred to in the
          bullet points above); and

     o    certain  other events that could have the effect of depriving  holders
          of Warrants of the benefit of all or a portion of the purchase  rights
          evidenced by the Warrants.

     No adjustment in the exercise price will be required unless such adjustment
would  require an  increase  or  decrease  of at least one  percent  (1%) in the
exercise price. However, any adjustment that is not made will be carried forward
and taken into account in any subsequent adjustment.

     "Fair  Market  Value" per  security at any date of  determination  shall be
determined in one of two ways:

          Listed  Securities:  If the  security  is  listed on any  exchange  or
          -------------------
     admitted  for trading on the Nasdaq  Stock  Market,  the Fair Market  Value
     shall be the average of the last  reported  sale prices over the 20 trading
     days  ending  on  the  date   immediately   preceding   the  date  of  such
     determination, or, if no such sale takes place on any such day, the closing
     bid price, in either case as reported for consolidated  transactions on the
     principal  securities  exchange  (including the Nasdaq National  Market) on
     which such  security is listed or admitted  for  trading.  However,  if any


                                      -24-

<PAGE>

     event that results in an adjustment of the exercise price occurs during the
     period  beginning on the first day of such 20-day  period and ending on the
     date immediately preceding the date of determination, the Fair Market Value
     as determined  pursuant to the foregoing will be appropriately  adjusted to
     reflect the occurrence of such event.

          Unlisted Securities:  If the security is not listed on any exchange or
          --------------------
     admitted  for trading on the Nasdaq  Stock  Market,  the Fair Market  Value
     shall be calculated as follows:  If the security is sold to a party that is
     not an affiliate of ours in an  arm's-length  transaction,  the Fair Market
     Value is the price per  security  at which such  security  is sold.  If the
     security  is sold to an  affiliate  of ours,  the  Fair  Market  Value  is:


          o    the last price per security at which such  security was sold in a
               non-affiliate  sale within the three-month  period preceding such
               date of determination;

          o    a price  determined  by a  majority  of the  Board of  Directors,
               including a majority of the Disinterested Directors, and approved
               in a board resolution delivered to the warrant agent; or

          o    a price determined by a nationally recognized investment banking,
               appraisal or valuation firm, which is not an affiliate of ours.

          In  addition,  the  calculation  of the Fair Market Value for sales to
     affiliates  must take into account,  among other factors deemed relevant by
     the Board of Directors or such investment  banking,  appraisal or valuation
     firm,  the  trading  price and  volume  of such  security  on any  national
     securities exchange or automated quotation system on which such security is
     traded.

     "Disinterested  Director"  means,  for  any  issuance  of  securities  that
requires a determination  of the Fair Market Value,  each member of the Board of
Directors who is not an officer,  employee,  director or other  affiliate of the
party  to  whom  we  are  proposing  to  issue  the  securities   requiring  the
determination.

     In case of certain consolidations or mergers of the Company, or the sale of
all or  substantially  all of the assets of the Company to another  corporation,
each Warrant shall  thereafter be exercisable  for the right to receive the kind
and  amount of shares of stock or other  securities  or  property  to which such
holder  would have been  entitled as a result of such  consolidation,  merger or
sale had the Warrants been exercised  immediately  prior to the consolidation or
merger. In addition, the person formed by or surviving any such consolidation or
merger (if other than the Company),  or to which such sale shall have been made,
will assume our obligations under the warrant agreement.

We Have Reserved Sufficient Shares
- ----------------------------------

     We have authorized and reserved for issuance the number of shares of common
stock that will be issuable upon the exercise of all outstanding Warrants. These
shares  of common  stock,  when paid for and  issued,  will be duly and  validly
issued,  fully paid and non-assessable,  free of preemptive rights and free from
all taxes, liens, charges and security interests.

                                      -25-




<PAGE>


We May Amend the Warrant Agreement
- ----------------------------------

     From time to time,  the Company and the warrant agent,  without  consent of
the holders of the Warrants,  may amend or supplement the warrant  agreement for
certain   purposes.   We  may  amend  the  agreement  to  cure  any  defects  or
inconsistencies.  We may also amend the  agreement  to make  changes that do not
materially  adversely  affect  the  rights  of  any  holder.  Any  amendment  or
supplement to the warrant  agreement  that has a material  adverse effect on the
interests  of the holders of the Warrants  requires  the written  consent of the
holders of a  majority  of the then  outstanding  Warrants.  We must  obtain the
consent of each holder of the Warrants  affected if a proposed  amendment  would
increase  the  exercise  price or decrease  the number of shares of common stock
purchasable  upon  exercise of  Warrants  (other  than  pursuant to  adjustments
provided for in the warrant agreement as generally described above).

We Will File Reports With the Warrant Agent
- -------------------------------------------

     Whether or not required by the rules and regulations of the SEC, so long as
any of the Warrants remain  outstanding,  we will file copies of certain reports
with the  warrant  agent and the  warrant  agent will mail these  reports to the
holders at their addresses  appearing in the register of Warrants  maintained by
the warrant agent.


                          DESCRIPTION OF CAPITAL STOCK
                          ----------------------------

     Our authorized capital stock consists of 75,000,000 shares of common stock,
par value $0.01 per share and 200,000 shares of preferred stock, par value $0.01
per share.

Common Stock
- ------------

     On  February  26,  1999,  there  were  32,237,078  shares of  common  stock
outstanding, held of record by 275 stockholders.

     The holders of common stock are entitled to one vote for each share held of
record on all matters submitted to a vote of the stockholders. Cumulative voting
applies  to the  election  of  directors.  Subject  to  preferences  that may be
applicable to any then-outstanding  preferred stock, holders of common stock are
entitled to receive  ratably  such  dividends as may be declared by the Board of
Directors  out of  legally  available  funds.  In the  event  of a  liquidation,
dissolution  or  winding-up  of the  Company,  holders of the  common  stock are
entitled to share ratably in all assets  remaining  after we pay our liabilities
and the liquidation preference of any then-outstanding preferred stock. With two
exceptions,  there are no preemptive,  subscription,  redemption or sinking fund
provisions  applicable  to  the  common  stock.  The  two  exceptions  are:  (1)
provisions  of the  preferred  stock  described  below and (2)  provisions of an
existing  stockholders'  agreement as to  redemption if alien  ownership  issues
arise.  All  outstanding  shares of common  stock are,  and all shares of common
stock to be outstanding upon completion of the offering will be,  fully-paid and
nonassessable.

     Our  Certificate  of  Incorporation  requires  cumulative  voting  for  the
election of directors.  Under cumulative voting, each stockholder is entitled to


                                      -26-

<PAGE>


cast as many  votes in the  election  as equals  the  product  of the  number of
directors to be elected and the aggregate  number of shares of common stock held
by such  stockholder.  The  stockholder  may cumulate such votes for one or more
directors as the stockholder  determines.  Under cumulative voting,  assuming 10
directors  were  to be  elected  and  32,237,07  shares  of  common  stock  were
outstanding,  a  stockholder  would  have to hold at least  2,930,643  shares of
common stock to be certain of electing one director.

Preferred Stock
- ---------------

     The Board of Directors may issue  preferred stock in one or more series and
may fix the  designations,  preferences,  powers  and  relative,  participating,
optional and other rights,  qualifications,  limitations and restrictions on the
preferred stock,  including the dividend rate, conversion rights, voting rights,
redemption price and liquidation preference, and may fix the number of shares to
be  included  in any such  series.  Any  preferred  stock may rank senior to the
common  stock  for  the  payment  of  dividends  or  amounts  upon  liquidation,
dissolution or winding-up,  or both. In addition,  any shares of preferred stock
may have class or series voting  rights.  We do not have any shares of preferred
stock  outstanding.  Issuances  of  preferred  stock,  while  providing  us with
flexibility  in connection  with general  corporate  purposes,  may, among other
things,  have an adverse  effect on the rights of holders of common  stock.  The
Board of Directors, without stockholder approval, can issue preferred stock with
voting and conversion  rights that could  adversely  affect the voting power and
other rights of holders of common  stock.  Preferred  stock could thus be issued
quickly  with  terms  calculated  to delay or prevent a change of control of the
Company  or to make  the  removal  of  management  more  difficult.  In  certain
circumstances,  this could have the effect of decreasing the market price of the
common stock.

Certain Provisions of the Company's Certificate of Incorporation and Bylaws
- ---------------------------------------------------------------------------

     Certificate of  Incorporation.  As currently in effect,  our Certificate of
     ------------------------------
Incorporation  may not be amended,  modified,  rendered  ineffective or repealed
except by the vote of the holders of  two-thirds  of the issued and  outstanding
shares of common  stock.  Except as required by law,  other classes or series of
stock will not be entitled to vote on any such amendment,  modification or other
change, unless and to the extent required by any applicable law. Our Certificate
of  Incorporation  currently  requires  the  affirmative  vote of the holders of
two-thirds of the issued and outstanding shares of common stock to approve:

     o    our merger or consolidation with or into any other entity;

     o    our dissolution or liquidation; or

     o    the  sale,  exchange  or  lease  of  all or  substantially  all of our
          property and assets.

     The  Certificate  of  Incorporation  also requires that at each election of
directors by the holders of common stock, all directors must be elected.

     Bylaws.  As  currently  in  effect,  our  Bylaws  require  that there be 10
     -------
directors on the Board of Directors. The Bylaws provide that special meetings of
the stockholders generally may be called by the president and shall be called at
the request of the holders of at least one-third of the common stock then issued


                                      -27-

<PAGE>


and outstanding.  A special meeting solely to elect all directors of the Company
shall be called at the  written  request of a holder or  holders  of  sufficient
shares of common stock to then elect at least one director  under  principles of
cumulative  voting.  The Bylaws  also  provide  that  except as  provided in the
Certificate of Incorporation or the Bylaws,  the Bylaws may be altered,  amended
or repealed or new Bylaws may be adopted only upon the vote of either:

     o    three-fourths  of the members of the Board of Directors then in office
          or

     o    the  holders of  two-thirds  of the issued and  outstanding  shares of
          common stock.


                                 LEGAL MATTERS
                                 -------------

     Certain legal matters with respect to the shares of common stock offered by
this prospectus  will be passed upon for the Company by Randy Segal,  our Senior
Vice President,  General Counsel and Secretary. Ms. Segal owns 156,841 shares of
common  stock.  Ms.  Segal's  ownership  includes  shares she owns  through  our
matching  401(k) Plan and /or Employee  Stock  Purchase Plan. Her ownership also
includes  shares  issuable upon the exercise of options  granted under the Stock
Option Plan which options are vested and exercisable, subject to compliance with
applicable securities laws.


                                     EXPERTS
                                     -------

     The  consolidated   financial   statements  of  American  Mobile  Satellite
Corporation  as of  December  31, 1997 and 1998 and for each of the years in the
three-year  period ended  December 31, 1998,  incorporated  by reference in this
registration  statement,  have been audited by Arthur Andersen LLP,  independent
public accountants,  as indicated in their report with respect thereto,  and are
incorporated by reference  herein in reliance upon the authority of said firm as
experts in giving said  report.  The  consolidated  financial  statements  of XM
Satellite  Radio Holdings Inc. (a development  stage Company) as of December 31,
1998 and 1997, for the years ended December 31, 1998 and 1997 and for the period
from December 15, 1992 (date of inception)  through December 31, 1998, have been
incorporated by reference herein and in the  registration  statement in reliance
upon  the  report  of  KPMG  LLP,  independent   certified  public  accountants,
incorporated by reference herein, and upon the authority of said firm as experts
in  accounting  and  auditing.  The report of KPMG LLP covering the December 31,
1998  consolidated  financial  statements  of XM Satellite  Radio  Holdings Inc.
contains an explanatory paragraph that states that the Company has not commenced
operations,  has negative  working capital of $130,341,000 and is dependent upon
debt and equity  financings which raise  substantial  doubt about its ability to
continue  as a going  concern.  The  consolidated  financial  statements  do not
include any adjustments that might result from the outcome of that uncertainty.


                       WHERE YOU CAN FIND MORE INFORMATION
                       -----------------------------------

     We file annual,  quarterly and special reports,  proxy statements and other
information  with the SEC.  You may  read and copy any  document  we file at the
SEC's  public  reference  rooms in  Washington,  D.C.,  New  York,  New York and
Chicago, Illinois. Please call the SEC at 1-800-SEC-0330 for further information
on the public  reference rooms. Our SEC filings are also available to the public
at the SEC's web site at http://www.sec.gov. You also may find information about
us on our web site at http://www.ammobile.com.

                                      -28-

<PAGE>


     The SEC allows us to incorporate by reference the information  that we file
with the SEC, which means that we can disclose  important  information to you by
referring you to those documents.  The information  incorporated by reference is
considered to be part of this  prospectus,  and  information  that we file later
with the SEC will  automatically  update  and  supersede  this  information.  We
incorporate 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; and

     b. the  description  of  our  capital  stock  contained in our registration
        statement  on Form 8-A, dated  December 9, 1993 and on Form 8-A/A, dated
        December 13, 1993.

     You may  request  a copy of  these  filings,  at no  cost,  by  writing  or
telephoning us 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) 758-6130

     No  person  has  been  authorized  to give any  information  or to make any
representation  other than those contained in this prospectus in connection with
the offering of the Warrants and the common stock  issuable upon the exercise of
Warrants.  If information or representations are given or made you must not rely
on it as if we authorized  it.  Neither the delivery of this  prospectus nor any
sale made hereunder shall, under any  circumstances,  create an implication that
the information  contained or incorporated by reference  herein is correct as of
any time  subsequent to its date or that there has been no change in the affairs
of the Company since such date.  This prospectus does not constitute an offer to
sell or a solicitation  of an offer to buy any securities  offered hereby in any
jurisdiction in which such offer or solicitation is not permitted,  or to anyone
whom it is unlawful to make such offer or solicitation.


                                      -29-




<PAGE>





The  information in this  prospectus is not complete and may be changed.  We may
not sell  these  securities  until the  registration  statement  filed  with the
Securities and Exchange Commission is effective.  The prospectus is not an offer
to  sell  these  securities  and it is not  soliciting  an  offer  to buy  these
securities in any state where the offer or sale is not permitted.



                             Subject to Completion

                              Dated March 31, 1999
                                                                      Prospectus
                      AMERICAN MOBILE SATELLITE CORPORATION

                        11,357,278 Shares of Common Stock

     Under  this  prospectus,  two of our  stockholders  may  offer and sell our
common stock.

               Motorola, Inc.:           Up to 6,520,532 shares

               Singapore
               Telecommunications
               Ltd.:                     Up to 4,836,746 shares


     Our common stock is quoted on the Nasdaq  National  Market and traded under
the symbol "SKYC."

     Our  principal  executive  offices  are located at 10802  Parkridge  Blvd.,
Reston,Virginia 20191-5416, and our telephone number is (703) 758-6000.

                               ------------------

     See "Risk Factors" beginning on page 5 for a discussion of certain material
factors that you should  consider in connection with an investment in our common
stock. 
                               ------------------

     Neither the  Securities and Exchange  Commission  nor any state  securities
commission has approved or  disapproved  of these  securities or passed upon the
adequacy or accuracy of this prospectus. Any representation to the contrary is a
criminal offense.

     The date of this prospectus is March 31, 1999.





<PAGE>




                                TABLE OF CONTENTS
                                -----------------

                                                                            Page

Prospectus Summary.............................................................2
         The Company...........................................................2
         The Offering..........................................................3
Risk Factors...................................................................5
Use of Proceeds...............................................................16
Selling Stockholders..........................................................16
Registration Rights of Selling Stockholders...................................19
Plan of Distribution..........................................................20
Description of Capital Stock..................................................22
Legal Matters.................................................................24
Experts.......................................................................24
Where You Can Find More Information...........................................24

================================================================================





     This  prospectus  contains and  incorporates  by reference  certain forward
looking  statements  within the  meaning of the  Private  Securities  Litigation
Reform Act of 1995 with respect to our business, financial condition and results
of operations,  including,  without  limitation,  statements  under the captions
"Business" and "Management's  Discussion and Analysis of Financial Condition and
Results of  Operations"  in our  annual and  quarterly  reports.  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.  Factors that may cause actual
results to differ  materially  from those  contemplated  by such forward looking
statements  include,  among others, the factors discussed in the section of this
prospectus entitled "Risk Factors."






<PAGE>





                               PROSPECTUS SUMMARY
                               ------------------

     The  following  summary  is  qualified  in its  entirety  by  the  detailed
information and financial statements,  including the notes thereto, contained or
incorporated by reference in this prospectus.

                                   The Company
                                   -----------

     The  Company  was  incorporated  on May 3,  1988.  At  that  time,  the FCC
determined  that the public  interest  would be best served by granting a mobile
satellite  services  license  to a  consortium  of  all  willing  and  qualified
applicants.  The Company was formed by eight of the initial  applicants for that
license.  The FCC  authorized  us to  construct,  launch,  and  operate a mobile
satellite  services  system  to  provide a full  range of mobile  voice and data
services via satellite to land, air and sea-based  customers.  On April 7, 1995,
we  successfully  launched our first  satellite,  MSAT-2,  from Cape  Canaveral,
Florida.

                                Our service area:
                                -----------------

o The continental United States        o Alaska
o Hawaii                               o Puerto Rico
o The U.S. Virgin Islands              o United States coastal waters
o International waters and airspace    o Any foreign territory where the local
                                         government has authorized the provision
                                         of service

     Our wholly-owned  subsidiary,  AMSC Acquisition Company,  Inc. operates our
mobile  satellite  services.  On  March  31,  1998  we  acquired  (through  AMSC
Acquisition) ARDIS Company,  then a wholly-owned  subsidiary of Motorola,  Inc.,
that owns and  operates  a two-way  wireless  data  communications  network.  We
purchased  ARDIS for  approximately  $50  million in cash and $50 million in our
common stock.  Through the acquisition of ARDIS, we became a nationwide provider
of  wireless  communications  services,  including  data,  dispatch,  and  voice
services. We primarily serve business customers in the United States.

     On October 16, 1997,  our  indirect  subsidiary,  XM  Satellite  Radio Inc.
(formerly American Mobile Radio Corporation), received a license from the FCC to
provide satellite-based Digital Audio Radio Service (DARS) throughout the United
States.  XM Radio bid $89.9 million at auction on April 2, 1997 for the license.
XM Radio has and will continue to be funded by parties other than the Company in
exchange  for debt and  equity  interests  in XM Radio.  Accordingly,  we do not
expect that the  development of this business will have a material impact on our
financial  position,  results  of  operations,  or cash  flows.  XM  Radio is an
indirect subsidiary that we own through our direct subsidiary XM Satellite Radio
Holdings Inc. (formerly AMRC Holdings, Inc.).

     As a result of the  combination  of our  satellite-based  business with the
ARDIS  terrestrial-based  business,  we now  offer a broad  range of  end-to-end

                                      -2-


<PAGE>


wireless  solutions  utilizing a seamless  network  consisting  of the  nation's
largest,  most fully-deployed  terrestrial wireless data network and a satellite
in geosynchronous  orbit. Our satellite-only data communications system provides
data  services  primarily  to  long-haul  trucking  customers.   Our  multi-mode
communications system uses both our terrestria and satellite networks to provide
"least-cost  routing"  for two-way data  communications.  We are able to provide
cost-effective  nationwide  coverage for communications  outside the terrestrial
network  coverage  area by  routing  messages  over the lower  cost  terrestrial
network before  automatically  routing messages over the satellite network.  Our
terrestrial network delivers superior in-building penetration,  completion rates
and response times compared to other wireless data networks through the use of a
single frequency reuse technology.

     In addition to providing  data service,  we offer two forms of mobile voice
communications  service:  nationwide  dispatch  service and satellite  telephone
service.  We are the only  company to offer a nationwide  dispatch  service that
allows  multiple  users  located  anywhere in our service area to share a single
connection for point-to-multipoint communication using push-to-talk handsets. We
market our nationwide  dispatch  service  primarily to field services users with
wide-area fleet  communications  needs. Our satellite telephone service provides
traditional  voice,  fax and data service through  satellite  terminals that are
similar to cellular phones. We market our satellite  telephone service primarily
to maritime users, including both commercial and recreational vessels, and other
targeted market segments such as government, public safety organizations and the
natural resource industries.


                                  The Offering
                                  ------------

Securities...........................Offered  (1)  Motorola   may  offer  up  to
                                     6,520,532  shares  of our common stock; and
                                     (2)  Singapore  Telecom   may  offer  up to
                                     4,836,746 shares of our common stock.

Listing or Quotation
of Common Stock......................Our  common  stock  is traded on the Nasdaq
                                     National Market under the symbol "SKYC."

Registration.........................The   registration  rights  agreement  with
                                     Motorola dated March 31, 1998, requires  us
                                     to register for resale the shares of common
                                     stock  Motorola  holds.   An  amended  and
                                     restated registration rights agreement with
                                     Singapore  Telecom  also  dated  March  31,
                                     1998,  requires  us  to register for resale
                                     the  shares  of  common  stock  Singapore
                                     Telecom  holds  and  to  register shares of
                                     common  stock issuable to Singapore Telecom
                                     upon its exercise of warrants it holds.

                                      -3-

<PAGE>
                                     The agreements also require  us  to prepare
                                     and  file  with  the  SEC  amendments  and
                                     supplements  to  the registration statement
                                     and  this  prospectus that are necessary to
                                     keep the registration statement effective.

Use of Proceeds......................We  will not  receive any proceeds from the
                                     sale  of  our  common stock covered by this
                                     prospectus.






                                      -4-


<PAGE>





                                  RISK FACTORS
                                  ------------

We Have Substantial and Continuing Operating Losses
- ---------------------------------------------------

     We have incurred  significant  operating  losses and negative cash flows in
each year since we began operations.  These losses are due primarily to start-up
costs,  the  costs of  developing  and  building  each  network  and the cost of
developing,  selling and providing our products and services. For the year ended
December 31, 1998, we reported operating losses of approximately  $88.2 million.
For historical  periods prior to our acquisition of ARDIS, we reported operating
losses  of  approximately  $97.4  million  and $120  million  in 1997 and  1996,
respectively.  During these same periods,  ARDIS  reported  operating  losses of
approximately  $17.4  million and $29.2  million.  We expect to continue to make
significant capital outlays for the foreseeable future to fund interest expense,
capital  expenditures  and working capital before we begin to generate  positive
cash flow from  operations.  These  outlays are  expected  to  continue  for the
foreseeable future thereafter.  We cannot guarantee that we will have sufficient
resources to complete the expenditures required to operate the business.

     Since inception, we have been engaged in operating our business, recruiting
key  management  and  technical  personnel  and  raising  capital  to  fund  our
operations and the  development of our networks.  We launched  commercial  voice
service in January  1996.  Accordingly,  you only can evaluate our  prospects in
each of our markets based on this short operating history. You must consider the
prospects for our success in light of the risks, expenses and difficulties often
encountered  when  establishing  a new business in an evolving  industry that is
subject  to rapid  technological  and price  changes,  and  characterized  by an
increasing number of market competitors.

     We estimate that we will not have  sufficient  operating  revenues to cover
operating expenses for the foreseeable  future. Our ability to generate positive
operating  cash flow will depend  upon,  among  other  factors,  the  successful
integration of ARDIS into our operations,  the  achievement of related  business
synergies and the successful marketing of our services. We cannot guarantee that
the ARDIS integration,  the achievement of related business  strategies,  or our
marketing efforts will be successful.

     In addition, we will require additional capital for expenditures  necessary
to further develop our business and expand our networks.

We Are Highly Leveraged
- -----------------------

     As of December  31,  1998,  our  indebtedness  totaled  approximately  $486
million ($478 million net of debt discount).  As of December 31, 1998 we had $68
million  available  under AMSC  Acquisition  Company,  Inc.'s  revolving  credit
facility.  ARDIS  received a commitment  from  Motorola for up to $10 million of
vendor financing for certain capital  expenditures.  On a pro forma basis, after
giving effect to the acquisition of ARDIS and the related  financing as if these
transactions  had been  consummated  on January 1 of the period  presented,  our
earnings   would  have  been   insufficient   to  cover  our  fixed  charges  by
approximately  $176.2  million for fiscal  1997 and $151.6  million for the year
ended  December 31, 1998.  At December 31, 1998 our  stockholders'  equity was a
deficit  of  approximately  $24.4  million.  We and  our  subsidiaries  will  be
permitted to incur additional indebtedness in the future.

                                      -5-

<PAGE>

     Beginning April 1, 2001, AMSC  Acquisition,  our  wholly-owned  subsidiary,
will be allowed to pay dividends to us. This will permit us to meet our interest
expenses with respect to our $100 million term loan facility.  Historically,  we
have not generated sufficient earnings or cash flow from operations to make such
interest payments.

     The degree to which we are leveraged  could have important  consequences to
the success of our business including, but not limited to:

     o    increasing  our vulnerability to general adverse economic and industry
          conditions;

     o    limiting  our  ability  to  obtain additional financing to fund future
          working  capital,  capital  expenditures, research and development and
          other general corporate requirements;

     o    requiring  the  dedication  of  a substantial portion of our cash flow
          from  operations  to the payment of principal of, and interest on, our
          indebtedness,  thereby  reducing the availability of such cash flow to
          fund working  capital, capital  expenditures, research and development
          or for other general corporate purposes;

     o    limiting  our flexibility in  planning for, or reacting to, changes in
          our business and the industry; and

     o    placing us  at a  competitive  disadvantage  vis-a-vis  less leveraged
          competitors.

We May Need Additional Capital
- ------------------------------

     We expect to  continue  to make  significant  outlays  for the  foreseeable
future to fund debt service, capital expenditures and working capital. This will
continue until we begin to generate  positive cash flow from  operations and for
the foreseeable  future  thereafter.  If our cash flows from operations are less
than projected,  we will require  additional debt or equity financing in amounts
that could be substantial. The type, timing and terms of financing we may select
will depend upon our cash needs the availability of other financing  sources and
the prevailing  conditions in the financial markets. We cannot guarantee that we
will be able to find any such sources at any given time on favorable terms.

     Motorola  has entered  into an agreement  with our  wholly-owned,  indirect
subsidiary,  ARDIS, to provide up to $10 million of vendor financing, which will
be available to finance up to 75% of the purchase  price of  additional  network
base stations necessary to meet the build-out requirements under a contract AMSC
Acquisition has with the United Parcel  Service.  Funds borrowed under this loan
agreement  have an  interest  rate  equal  to  LIBOR  plus  7% and  the  loan is
guaranteed by us and each subsidiary of AMSC Acquisition.  The terms of the loan
require that amounts  borrowed be secured by the  equipment  purchased  with the
loan. As of December 31, 1998, we had borrowed $1.6 million from Motorola  under
this loan.


                                      -6-

<PAGE>


     We  cannot  guarantee  that  our  current  projection  of  cash  flow  from
operations will be accurate.  Our  projections  will depend upon numerous future
factors and  conditions,  many of which are outside of our  control.  You should
note that  projections  are  merely  estimates  of future  events and you should
expect actual events to vary from current  estimates,  possibly  materially.  In
addition,  if  customer  demand  exceeds  our  current  expectations  and we can
accommodate such demand without  adversely  affecting th quality of our service,
we are likely to attempt to accelerate our expansion.  If we elect to accelerate
our  build-out or introduce  new  products or services,  our funding  needs will
increase,  possibly to a significant degree. We cannot guarantee that we will be
able to secure any additional  financing on commercially  reasonable terms or at
all. Our cost of expanding our network and  operating  our business,  as well as
our revenues, will depend on a variety of factors including:

     o    our ability to meet our expansion schedules;

     o    the number of customers and the services for which they subscribe;

     o    the nature and penetration of new services that we and our competitors
          may offer;

     o    regulatory changes; and

     o    changes in technology.

As a result,  our actual  costs and  revenues  may vary from  expected  amounts,
possibly to a material  degree.  Such variations are likely to affect our future
capital  requirements.  Accordingly,  it is possible that we will be required to
raise  substantial  additional  capital  in  the  future  or  that  our  current
projections will prove to be inaccurate.

Our Market Is Rapidly Changing
- ------------------------------

     The  markets for  wireless  communications  services  change  rapidly.  Our
success  depends,  in part, on our ability to respond and adapt to such changes.
We cannot guarantee that we will be able to compete effectively under, or adjust
our contemplated  plan of development to meet,  changing market  conditions.  We
cannot  guarantee  that we will be able to  implement  our  strategy or that our
strategy will be successful in this rapidly evolving market.

     This market is also marked by the continuous  introduction  of new products
and services and  increased  capacity for services  similar to those we provide.
Future technological advances in the wireless communications industry may result
in the  availability  of new  products or  services.  Advances  may increase the
efficiency of existing products or services.  If a technology  becomes available
that is more  cost-effective or creates a superior product,  we may be unable to
access such technology or financ the necessary  substantial capital expenditures
that may be required.  Our  technology  may be rendered less  profitable or less


                                      -7-

<PAGE>


viable by  existing,  proposed  or as yet  undeveloped  technologies.  We cannot
guarantee  that we will have  available  the  financial  and other  resources to
compete  effectively  against  companies  possessing such  technologies.  We are
unable to predict which of the many possible  future  products and services will
meet evolving industry  standards and consumer demands.  We cannot guarantee tha
we can adapt to such technological changes or offer such products or services on
a timely basis or establish or maintain a competitive position.

We Depend on Market Acceptance
- ------------------------------

     Our success is subject to a number of business,  economic,  regulatory  and
competitive factors, many of which are beyond our control,  including the extent
to which prospective  customers will purchase our services.  The vitality of our
business is subject to the  successful  implementation  of our growth  strategy,
which, in turn, depends,  among other things, on our expectation that demand for
our services will increase  significantly  in the markets we serve.  We have not
yet  commercially  introduced  certain of these services and we cannot guarantee
that any of them will achieve  market  acceptance or result in the generation of
operating  cash flow.  Failure to gain market  acceptance for current or planned
products and services would have a material  adverse effect on our business.  In
addition,  we have  incurred and will  continue to incur  significant  operating
expenses.

     Based upon certain expectations as to the anticipated market acceptance of,
and customer demand for, our services,  we have made, and will continue to make,
significant capital investments. Based on similar expectations, our subsidiaries
have entered into  operating  leases,  equipment  supply  contracts  and service
arrangements, and are attempting to secure financing.  Accordingly, any material
miscalculation  with respect to our  operating  strategy or business  plan could
have a material adverse effect on our business.

We Must Effectively Manage Our Growth
- -------------------------------------

     In our continuing efforts to respond to changing market conditions,  we may
experience periods of rapid expansion.  In order to manage growth effectively in
the  complex  environment  in which we  operate,  we will need to  maintain  and
improve our  operating and  financial  systems and expand,  train and manage our
employee  base.  We must  expand the  capacity  of our sales,  distribution  and
installation  networks in order to achieve  continued growth in our existing and
future markets.  In general, if we fail to manage growth effectively there could
be a material adverse effect on our business, financial condition and results of
operations.

Our Customers Are Highly Concentrated
- -------------------------------------

     After  accounting for the acquisition of ARDIS,  five customers  (including
IBM) accounted for an aggregate of 40% of our service revenue for the year ended
December 31,  1998.  The loss of one or more of these  customers,  or any event,
occurrence or development  which adversely  affects our relationship with one or
more of these customers could have a material adverse effect on our business.




                                       -8-


<PAGE>



We Rely on Third Party Vendors
- ------------------------------

     We  rely  on  independent  vendors  to  develop  and  manufacture  wireless
communications  devices for our networks,  which are significant elements of our
business  plan.  These  suppliers do not sell such devices to us on an exclusive
basis.  We carry a limited  inventory  of such  devices  and  generally  have no
guaranteed  supply  arrangements.   From  time  to  time,  we  have  experienced
interruptions  and/or  delays of supply.  We cannot  guarantee  that we will not
experience such  interruptions  in the future.  In addition,  we have short-term
contracts  with the  majority of our  suppliers.  We cannot  guarantee  that our
suppliers will continue to provide  products to us at attractive  prices,  or at
all, or that we will be able to obtain such products in the future from these or
other providers on the scale and within the time frames we require.  Some or all
of our suppliers could enter into exclusive  arrangements  with our competitors,
or cease selling these components to us at commercially reasonable prices, or at
all. If we fail to obtain such products on a timely basis at an affordable cost,
or experience any significant  delays or interruptions  of supply,  our business
would be materially adversely affected.

     As part of our growth strategy, we rely on our suppliers to reduce the cost
of  wireless  communications  devices  approved  and  available  for  use on our
network.  Our  management  believes  that  reductions  in the  cost of  wireless
communications  devices  will result in increased  sales of devices,  additional
subscribers  for  our  services  and a  corresponding  increase  in our  service
revenues.  If we fail to  obtain  such cost  reductions  on a timely  basis,  or
experience  any  significant  delays of such  reductions,  our business would be
materially adversely affected.

     We expect the anticipated expansion of our operations and infrastructure to
place a  significant  demand  on our  suppliers,  some  of  which  have  limited
resources and production capacity. In addition,  some of our suppliers, in turn,
rely on sole or  limited  sources  of supply for  components  included  in their
products.  If our suppliers fail to adjust to meet such increasing demand,  they
may be unable to supply  devices in the  quantities  and the  quality and at the
times we require, or at all. If we are unable to obtain sufficient quantities of
sole or  limited  source  devices or to develop  alternative  sources,  we could
experience  delays and increased  costs in the expansion of our  operations  and
infrastructure  or become  unable to properly  maintain  our  existing  level of
operations.  Such  occurrences  could  have a  material  adverse  effect  on our
business, financial condition and results of operations.

The ARDIS Technology Is Subject to Competitive Risks
- ----------------------------------------------------

     The ARDIS network, and certain of its competitive  strengths,  such as deep
in-building   penetration,   is  based  upon  a  single  frequency  reuse  (SFR)
technology.  Motorola  holds  the  patent  for SFR  technology  and  ARDIS has a
non-exclusive  license to use the SFR  technology.  ARDIS also relies on support
agreements  with Motorola for support of the  operations of certain  portions of
the ARDIS  network.  However,  Motorola could enter into  arrangements  with our
competitors  and it is  possible  that such  agreements  could  have a  material
adverse effect on us. 


                                      -9-

<PAGE>

There Are Risks Associated With Satellite Technology
- ----------------------------------------------------

     We have an  agreement  with TMI, the Canadian  mobile  satellite  owner and
operator of MSAT-1,  for backup,  restoral and additional  capacity usage if our
satellite fails or we need  additional  capacity.  In return,  we have agreed to
provide TMI with similar  backup  service on our MSAT-2  satellite.  Each of the
MSAT-1 and MSAT-2  satellites  has in the past  experienced  some  technological
malfunctions.  While  recent  MSAT-2  malfunctions  have  involved  either spare
components or ones that did not have a materia impact on current operations,  it
is possible that either or both satellites could experience future  malfunctions
at any time.

MSAT-2  has an  expected  end of  service  life of 2006,  subject  to  potential
technological  failures  and other  factors.  For  example,  random  failure  of
satellite  components  could  result in damage to or loss of MSAT-2.  It is also
possible that either  satellite  could be damaged by  electromagnetic  storms or
collisions with other objects,  although such occurrences are rare. Although the
actual service lives of both satellites may exceed their expected service lives,
we cannot  guarantee  that the expected  service life of the  satellite  will be
achieved or  exceeded.  Although  we have  in-orbit  insurance  for a failure of
MSAT-2,  it is  unlikely  that any  recovery  under such  insurance  would fully
compensate us for losses we would sustain for such a failure.  In addition,  the
in-orbit  insurance  policy is subject  to annual or  biannual  renewal,  and we
cannot   guarantee  that  insurance  on  favorable  terms  and  at  commercially
reasonable rates will remain available for coverage of MSAT-2.


Our Remote Disaster  Recovery System for the Satellite Network Ground Segment Is
- --------------------------------------------------------------------------------
Limited
- -------

     Presently,  our disaster recovery systems focus on internal  redundancy and
diverse  routing  within  each of the  facilities  operated  by or for  us.  For
example,   the  ARDIS  terrestrial   network  has  access  to  a  remote  ground
communications  backup complex that would enable us to continue to provide ARDIS
services in the event of a natural disaster affecting one geographic site. We do
not,  however,  currently  have  access  to a  remote  backup  satellite  ground
communications  facility  that would  enable us to  continue  to process  mobile
satellite  communications  services  for  customers  in the  event of a  natural
disaster or other occurrence that rendered the system unavailable.  Our business
is subject to the risk that such a disaster or other  occurrence could hinder or
prevent  us from  continuing  to  provide  some  services  to some or all of our
customers.

Our Industry Is Highly Competitive
- ----------------------------------

     The  wireless   communications   industry  is  highly  competitive  and  is
characterized by frequent technological innovation.  The industry includes major
domestic and international companies,  many of which have financial,  technical,
marketing,  sales,  distribution and other resources  substantially greater than
ours and which  provide,  or plan to provide,  a wider range of services than we
will provide.  Our products and services compete with a number of communications
services,  including  existing  satellite  services,  terrestrial  air-to-ground

                                      -10-

<PAGE>


services,  and terrestrial  land-mobile and fixed services, and may compete with
new  technologies  in the future.  In addition,  the FCC has recently  allocated
large amounts of additional  spectrum for communications  uses or potential uses
that could compete with us. Additional allocations of spectrum for such uses may
occur in the future.

Our Business Is Subject to Regulatory Risks
- -------------------------------------------

     The ownership and  operations of our  communication  systems are subject to
significant  regulation by the Federal Communications  Commission.  The FCC acts
under  authority  granted by the  Communications  Act of 1934,  as amended,  and
related  federal  laws.  A number of our  licenses are subject to renewal by the
FCC.  Our  satellite   operations   are  subject  to   international   frequency
coordination.  Current FCC regulations generally limit the ownership and control
of our company by  non-U.S.  citizens or entities to no more than 25%. We cannot
guarantee that the rules and regulations of the FCC will continue to support our
operations as we presently  conduct them and plan to conduct them in the future.
We cannot  guarantee  that all existing  licenses  will be renewed and requisite
frequencies coordinated.

     There are  applications  by others  now  pending  before the FCC to use the
Inmarsat system and TMI's Canadian-licensed system, both of which operate in the
MSS L-band and have satellite  footprints covering the United States, to provide
service in the United  States.  We have opposed  these  filings.  In addition to
providing additional competition to us, a grant of domestic authority by the FCC
to use any of these foreign systems may increase the demand by these systems for
spectrum in the  international  coordination  process and could adversely affect
our ability to coordinate our spectrum access.

     On July 20,  1998,  the FCC granted  SatCom a Special  Temporary  Authority
(STA) to operate up to 500 mobile  terminals  for 180 days on a private  carrier
basis  so  that it may  conduct  marketing  trials;  this  STA was  subsequently
extended to July 12, 1999. On July 30, 1998, we filed an Application  for Review
and a Motion for Stay of this Special  Temporary  Authority  grant with the FCC,
and these filings remain pending.

Our Business Is Subject to the Year 2000 Problem
- ------------------------------------------------

     We have developed and are  implementing  a Year 2000  Readiness  Program to
address Year 2000 issues.  "Year 2000  Ready," or "Year 2000  Readiness,"  means
that  customers  will  experience  no material  difference  in  performance  and
functionality of our networks prior to, during or after the year 2000.

     Our Year 2000 Readiness  Program uses the phased  approach that is standard
in our  industry.  The  Awareness,  Inventory  and  Assessment  phases have been
completed,  and we are at various stages of the Renovation,  Validation/Test and
Implementation/Rollout phases, depending on the particular system involved.


                                      -11-


<PAGE>

     The  Inventory  and  Assessment  Phases  concentrated  on our core business
systems:  those systems, both hardware and software,  whose failure could have a
material  impact on our financial  condition and operations.  Vendors  providing
critical  products and services to us are also  included in this  definition  of
core business  systems.  Although the core business systems are the top priority
in our Year 2000 Readiness Program, we assessed all of our software and hardware
for Year 2000 Readiness.

     Our plans for the Renovation,  Validation/Test  and  Implementation/Rollout
Phases  call for us to be Year  2000  Ready by the end of the third  quarter  of
1999.  In  addition,   we  are  currently  scheduled  to  complete   renovation,
implementation and rollout of our internal systems (including our voice customer
billing  software,  CMIS) in the fourth quarter of 1999; these internal software
systems do not affect our ability to pass customer  traffic and  therefore  will
not affect Year 2000 Readiness. While there can be no assurances that we will be
successful  or that we will  complete  the Year 2000  Readiness  Program by that
time,  we  believe  we will  have  sufficient  time to make  our  core  systems,
including internal systems, Year 2000 Ready before December 31, 1999.

     The  complex  of  hardware  and  software  that  we  maintain  consists  of
commercial  off-the-shelf (COTS) software,  as well as custom software developed
specifically  for our networks.  In certain cases,  American  Mobile's Year 2000
Readiness  Program  involves  upgrading COTS software that is unsupported by the
vendor or whose Year 2000 Readiness could not be determined. Upgrading such COTS
software,  as  planned,  provides  greater  certainty  regarding  the Year  2000
Readiness of such products and ensures that vendor support will be available.

     The total cost of our Year 2000 Readiness  Program was  approximately  $2.4
million in 1998.  Expenditures  for the Year 2000 Readiness  Program in 1999 are
estimated to be up to $7.4  million.  Some  modification  costs,  including  the
purchase of software upgrades and consulting services,  are expensed as incurred
while other modification costs, such as hardware purchases, are being treated as
capital expenditures.

     The  estimated  cost and date on which we believe our network  will be Year
2000  Ready are  based on  management's  best  estimates.  However,  there is no
guarantee  that we will achieve  these  results and actual  results could differ
materially from those anticipated.  Nevertheless,  it is difficult or impossible
to foresee all the risks  associated  with  making our network  Year 2000 Ready.
Some of our critical business systems depend  significantly on software programs
and third party services that are not within our control.  Failure to solve Year
2000  errors  within our  critical  business  systems  could  result in possible
service outages,  miscalculations  or disruption of operations that could have a
material  impact on our business.  Our Year 2000  Readiness  Program may fail to
foresee  some risks or may not  address  them  adequately.  Because of our heavy
dependence  on  software,  some  Year  2000  problems  may not be  found  or the
remediation  efforts may introduce new bugs that are not identified  before they
impact operations. This applies to both COTS software and custom software.


                                      -12-


<PAGE>


     If our  customers  fail to become  Year 2000  ready on time with  their own
hardware and software systems,  their  applications may not function even if our
systems are Year 2000 Ready.  This will result in reduced  traffic and revenues.
Also, suppliers of goods and services may suffer Year 2000-related failures from
which we cannot adequately protect our business.

     While  management  believes  that we will be  able  to  achieve  Year  2000
Readiness in a timely manner,  the schedule for completing the implementation of
several core business  systems extends to the fourth quarter 1999 and there is a
possibility  that we may not become  Year 2000  Ready on time or within  budget.
Contingency  planning, as discussed below, is currently underway to minimize the
risk of  business  interruptions  caused by Year 2000  problems  within the core
business systems.

     We have contingency plans in place to minimize service  interruptions  that
can mitigate, although not eliminate, interruptions caused by problems resulting
from Year 2000 issues. For example, we have backup power supplies and generators
in place for certain  portions of our networks in the event of electrical  power
outages.  In addition,  for some services we have  contracted with more than one
service provider.  These plans, systems and services are being incorporated into
our Year  2000  contingency  planning.  To the  extent  that it is  commercially
reasonable to do so, we will include other  redundant or alternative  sources of
services in our Year 2000 contingency  planning  efforts.  We anticipate  having
additional Year 2000 contingency plans in place by June 1999.

Five Principal Stockholders Control The Company
- -----------------------------------------------

     Our principal  stockholders are Hughes  Communications  Satellite Services,
Inc.,  Motorola,  Baron  Capital,  Inc.,  Singapore  Telecom  and AT&T  Wireless
Services,  Inc. These stockholders hold in aggregate  approximately 75.7% of our
common stock on a fully diluted basis.  We have entered into material  contracts
and transactions with our principal  stockholders or their affiliates and we may
enter into additional  contracts in the future.  These contracts may include the
guarantee of our debt  obligations.  These  stockholders have other interests in
the communications  industry that may conflict with our interests.  Motorola and
Singapore Telecom are selling stockholders under this prospectus.

We Are Dependent On Our Key Personnel
- -------------------------------------

     We are dependent on the efforts of a group of employees  with technical and
business knowledge regarding our systems. If we lose the services of one or more
of these  individuals it could  materially and adversely affect our business and
our future  prospects.  We do not maintain key man life  insurance on any of our
officers or  employees.  Our future  success  will also depend on our ability to
attract and retain  additional  management and technical  personnel  required in
connection with the growth and development of our business. If we fail to retain
or attract such key personnel  there could be a material  adverse  impact on our
business, financial condition and results of operations.


                                      -13-


<PAGE>


Our Charter and Bylaws Contain Anti-takeover Provisions
- -------------------------------------------------------

     Our  Certificate  of  Incorporation  and  Bylaws and the  Delaware  General
Corporation Law contain provisions that may have the following effects:

     o    discouraging, delaying  or  making more difficult a change in control;
          and

     o    preventing the removal of incumbent directors.

     The existence of these provisions may negatively impact on the price of our
common stock and may discourage  third-party  bids.  These provisions may reduce
any premiums paid to stockholders  for their common stock.  Furthermore,  we are
subject to Section 203 of the  Delaware  General  Corporation  Law.  Section 203
governs business combinations with interested stockholders,  and also could have
the effect of delaying or preventing a change in control.

     Our  Certificate  of  Incorporation  also allows our Board of  Directors to
issue up to 200,000 shares of preferred stock and to fix the rights,  privileges
and  preferences  of such  shares  without  any  further  vote or  action by the
stockholders. If this preferred stock is issued in the future, the rights of the
holders may adversely affect the rights of the holders of common stock. While we
have no present  intention to issue shares of preferred stock, any such issuance
could be used to discourage, dela or make more difficult a change in control.

We Have Not Paid Dividends
- --------------------------

     We have not  declared or paid any  dividends  on our common stock since our
date of  inception.  We intend to retain any  earnings to support the growth and
development of our business and we have no present intention of paying dividends
in the  foreseeable  future.  In  addition,  our  ability  to pay  dividends  is
restricted by agreements we have made with several banks in connection  with our
loans and credit facility arrangements.

The Prices of Our Common Stock Could Be Volatile
- ------------------------------------------------

     Historically, the market prices for securities of emerging companies in the
telecommunications  industry  have been highly  volatile.  Future  announcements
concerning our business or the business of our competitors, including results of
technological  innovations,  new commercial products, or government  regulations
may have a  significant  impact on the  market  price of our common  stock.  Our
common stock has been thinly  traded since our initial  public  offering and its
price has been highly volatile in recent periods.

We Have Shares Eligible for Future Sales
- ----------------------------------------

     Future sales of substantial  amounts of our common stock, or the perception
that such sales may occur,  could adversely affect the value of the common stock

                                      -14-

<PAGE>


and could impair our ability to raise  additional  capital in the future through
the sale of equity securities. As of February 26, 1999, we had 32,237,078 shares
of common  stock  outstanding.  Of these  shares,  22,569,311  shares are freely
tradeable in the open market without  restriction or further  registration under
the Securities Act. The remaining  9,667,767  shares of common stock are subject
to various  registration  rights agreements,  lock-up agreements and shareholder
agreements.  In addition, if the holders of warrants issued as part of our March
1998  offering of units and  certain of our other  stockholders  exercise  their
warrants,   we  will  have  an  additional  2,071,259  shares  of  common  stock
outstanding,  all of which  will be freely  tradeable.  We also have  10,215,721
shares of common stock  subject to other  warrants  (including  warrants held by
Singapore  Telecom) or reserved for issuance to certain  stockholders  and under
certain  employee benefit and stock incentive plans, all of which are registered
for  resale or  subject  to  various  registration  rights  agreements,  lock-up
agreements and shareholder agreements. See "Description of Capital Stock."


                                      -15-

<PAGE>




                                 USE OF PROCEEDS
                                 ---------------

     We will not receive any proceeds from  Motorola's  or  Singapore  Telecom's
sale of our common stock.  Each of Motorola and  Singapore  Telecom will receive
all of the proceeds from its sale of shares of our common stock. We will use the
net proceeds that we realize from Singapore Telecom's exercise  of warrants,  if
any, for working capital and for general corporate  purposes,  at the discretion
of management.


                              SELLING STOCKHOLDERS
                              --------------------

Amount Offered By Selling Stockholders
- --------------------------------------

Motorola  acquired  6,520,532 shares of our common stock as part of the purchase
price we paid when we acquired its  subsidiary,  ARDIS,  in March 1998.  We also
paid Motorola $50 million in cash.  Singapore  Telecom currently holds 4,024,246
shares of our common stock that it acquired  from the following  sources:  (1) a
private  placement by us in 1993, (2) a conversion by Singapore  Telecom in 1993
of certain  convertible notes previously issued by us, and (3) acquisitions from
Mtel Space  Technologies,  L.P. in 1992 and 1995.  Singapore  Telecom also holds
warrants that entitle it to purchase  812,500 shares of our common stock,  which
shares  are also  covered  by this  prospectus.  We granted  these  warrants  as
consideration for Singapore  Telecom's  guaranty of some of our debt and some of
the debt of AMSC Acquisition Company.

     The  following  table shows,  as of March 9, 1999,  the number of shares of
common stock that each of the selling  stockholders  beneficially  owned and the
number of shares that each may offer under this  prospectus.  We cannot  provide
you with an  estimate  of the number of shares of common  stock that the selling
stockholders  will hold in the future.  This information is unavailable  because
the selling  stockholders  may sell all,  some or none of their shares of common
stock. The table has been prepared based upon information  furnished to us by or
on behalf of the selling stockholders.

<TABLE>
<CAPTION>

                            Shares Beneficially Owned Prior to Offering                                   
                            -------------------------------------------                              Shares Held
                         Number of Shares(1)           Percent(2)               Shares Offered    Following Offering
                         -------------------           ----------               --------------    ------------------


<S>                           <C>                         <C>                     <C>                    <C>
Motorola                      6,520,532                   20.23                   6,520,532              (4)

Singapore Telecom             4,836,746(3)                14.63                   4,836,746(3)           (4)

</TABLE>

- ------------
(1)  Reflects  beneficial  ownership  of shares of common  stock prior to giving
     effect to the sale of the shares offered in this prospectus. 



                                      -16-


<PAGE>

(2)  Reflects  the  percentage  of  the  outstanding   shares  of  common  stock
     beneficially owned.
(3)  Includes 812,500 shares of common stock issuable upon exercise of warrants.
(4)  We cannot  provide  you with an  estimate of the number of shares of common
     stock that the  selling  stockholders  will hold in the future  because the
     selling  stockholders  may sell all, some or none of their shares of common
     stock.

Motorola Has Material Relationships With Us
- -------------------------------------------

     Directors and Officers.  Motorola does not have,  and within the past three
     -----------------------
years has not had, any position or office with us or any of our  predecessors or
affiliates. 

     Participation  and Registration  Rights. In connection with our acquisition
     ----------------------------------------
of ARDIS,  Motorola  obtained  participation  rights with  respect to our common
stock pursuant to a participation rights agreement dated December 31, 1997 among
us, Motorola,  Singapore Telecom, Hughes Communications Satellite Services, Inc.
and certain other of our  stockholders.  If any of these  stockholders  wants to
transfer its shares of our common stock other than in a Rule 144 or public stock
exchange or Nasdaq Stock Marke  transaction  at a time when  Motorola owns 5% or
more of our common stock,  Motorola  would have a right to receive notice of the
intended transfer and a right to participate proportionately in the contemplated
transfer.  Likewise,  Motorola agreed to provide these stockholders with similar
notice and participation rights if Motorola decides to transfer its interests in
our  common  stock  under  similar  circumstances.   This  participation  rights
agreement and a registration  rights  agreement  with Motorola,  dated March 31,
1998,  each  give  Motorola  "demand"  and  "piggyback"  registration  rights as
described below. See "Registration Rights of Selling Stockholders - Motorola."

     Vendor  Financing.   Motorola  has  entered  into  an  agreement  with  our
     ------------------
wholly-owned, indirect subsidiary, ARDIS, to provide up to $10 million of vendor
financing, which will be available to finance up to 75% of the purchase price of
additional  network base stations  necessary to meet the build-out  requirements
under a contract that AMSC  Acquisition  has with UPS. Funds borrowed under this
loan  agreement  bear  interest at a rate equal to LIBOR plus 7% and the loan is
guarantied by us and each subsidiary of AMSC Acquisition.  The terms of the loan
require the amounts  borrowed to be secured by the equipment  purchased with the
loan. As of December 31, 1998, we had borrowed $1.6 million from Motorola  under
this loan.

Singapore Telecom Has Material Relationships With Us
- ----------------------------------------------------

     Directors and Officers.  Representatives  of Singapore Telecom have, within
     ----------------------
the past three years, served as directors of our company.

     Stockholders'  Agreement.  Singapore  Telecom  entered into a stockholders'
     ------------------------
agreement, amended and restated as of December 1, 1993, with us and other of our
stockholders including Hughes Communications  Satellite Services,  Inc. and AT&T

                                      -17-

<PAGE>


Wireless Services,  Inc. The stockholders'  agreement includes  provisions that,
among other things: 

     o    Limit our  activities  to providing  and  marketing  mobile  satellite
          service, designing, constructing, operating and maintaining our mobile
          satellite system, engaging in the communications business and engaging
          in necessary, appropriate or reasonably related activities.

     o    Require that the parties will not vote to remove  members of the Board
          of  Directors  except  for  cause,  and will not elect or  permit  the
          election of a director who is not a U.S. citizen, if such action would
          cause us to violate the law or FCC policy.

     o    Govern the  appointment  of the members of the Executive  Committee of
          the Board.

     o    Limit the  transferability of shares of our common stock to reduce the
          risk that we might  fail to  comply  with the  FCC's  restrictions  on
          non-U.S.  citizens owning our common stock, and thereby jeopardize our
          ownership  of  certain  FCC  licenses  issued to us that we require to
          operate our mobile satellite services system.

     The stockholders'  agreement can be terminated only by the affirmative vote
of the holders of three-fourths of the issued and outstanding  common stock held
by parties to the  agreement.  The agreement  may be amended by a  three-fourths
vote of  parties  holding  in  excess of 5% of our  common  stock,  except  that
amendments to provisions  relating to registration rights and some other matters
require the affirmative vote of the holders of three-fourths of the common stock
held by all parties to the agreement.

     Participation  Rights.  Under the  December 31, 1997  participation  rights
     ----------------------
agreement,  Singapore  Telecom  agreed  to  provide  Motorola  with  notice  and
participation  rights if  Singapore  Telecom  decides to transfer  shares of our
common stock,  other than in a Rule 144 or public stock exchange or Nasdaq Stock
Market  transaction,  at a time when  Singapore  Telecom  owns 5% or more of our
common  stock.   Motorola   granted   similar   rights  to  Singapore   Telecom.


     Guarantor.  Singapore Telecom is a guarantor of some of the debt we or AMSC
     ----------
Acquisition  Company owes. On June 28, 1996, we  established a $225 million debt
facility  of which $200  million  was  guarantied  by some of our  stockholders,
including  Singapore  Telecom.  In consideration  for this guaranty,  we granted
Singapore  Telecom  warrants to purchase our common stock.  In  connection  with
financing  the ARDIS  acquisition,  we refinanced  this debt and again  obtained
guaranties  from  some  of our  stockholders  including  Singapore  Telecom.  In
consideration  for its new guaranties,  we issued Singapore  Telecom  additional
warrants to purchase our common stock.

     Registration  Rights.  Pursuant to the amended  and  restated  registration
     ---------------------
rights  agreement  dated  March 31, 1998  entered  into in  connection  with the
refinancing and the related  guaranties,  we granted  Singapore Telecom "demand"
and  "piggyback"  registration  rights  for the shares issuable upon exercise of
all of these  warrants  and for other  restricted  securities  held by Singapore
Telecom as described below. See "Registration  Rights Of Selling  Stockholders -
Singapore Telecom."

                                      -18-

<PAGE>

                   REGISTRATION RIGHTS OF SELLING STOCKHOLDERS
                   -------------------------------------------

Motorola
- --------

     When we  issued  shares  of our  common  stock to  Motorola  as part of the
purchase  price for ARDIS,  we agreed to register  those shares for resale under
the  Securities  Act of 1933  pursuant  to the terms of a  participation  rights
agreement  with  Motorola  dated  December  31, 1997 and a  registration  rights
agreement with Motorola dated March 31, 1998. The registration  rights agreement
gave  Motorola a right to  "demand"  registrations  and a right to  include,  or
"piggyback," shares of common stock in other registrations.

     On no more than two occasions  after March 31, 1999, the first  anniversary
of our acquisition of ARDIS, the holders of at least 10% of the shares that were
issued to  Motorola  may  "demand"  that all or any  portion  of such  shares be
registered  under the Securities  Act,  subject to  registration  priorities and
postponement  rights of the Company.  The registration rights agreement requires
that one of these two demand registrations be an underwritten registration.

     The  registration  rights agreement also provides that any time after March
31,  1998,  whenever  we propose to  register  any of our  securities  under the
Securities Act,  whether or not for our own account,  on a form that may also be
used for the registration of the shares issued to Motorola,  the holders of such
shares may request that we include,  or "piggyback," all of their shares in such
registration.  If piggyback  registrations are underwritten  registrations,  the
registration  rights agreement sets forth requirements  relating to the priority
for inclusion of the holders' shares.

     The  registration  statement  of which this  prospectus  is a part is being
filed pursuant to the requirements of the warrant  registration rights agreement
between us and the  placement  agents for our March 31, 1998 offering of 335,000
units.  Motorola,  as the sole holder of the 6,520,532 shares of common stock we
issued in connection with our acquisition of ARDIS,  has exercised its piggyback
registration  rights and is offering up to 6,520,532  shares of our common stock
to the  public  at the same  time a the  registration  of the  warrants  and the
underlying shares is deemed effective under the Securities Act.


                                      -19-

<PAGE>


Singapore Telecom
- -----------------

Under the guaranty issuance agreement and the amended and restated  registration
rights  agreement with Singapore  Telecom,  each dated March 31, 1998, we agreed
under specified conditions to register for resale the shares of our common stock
already held by Singapore  Telecom,  and register the shares of our common stock
to be issued upon the  exercise of the warrants  issued to Singapore  Telecom in
connection with its 1996 and 1998 guaranties.

     At any time  prior to March 31,  2005,  the  holders of at least 25% of the
shares  that are  eligible  for  registration  under the  amended  and  restated
registration  rights  agreement  may  "demand"  that all or any  portion of such
shares  be  registered   under  the  Securities  Act,  subject  to  registration
priorities and postponement rights of the Company.

     The registration rights agreement also provides that whenever we propose to
register any of our securities  under the Securities Act, whether or not for our
own account,  on a form that may also be used for the registration of the shares
that are eligible for registration  under the amended and restated  registration
rights  agreement,  the holders of such shares may request  that we include,  or
"piggyback,"   all  of  their   shares  in  such   registration.   If  piggyback
registrations are underwritten registrations,  the registration rights agreement
sets forth  requirements  relating to the priority for inclusion of the holders'
shares.

     Singapore  Telecom,  as (1) the sole holder of  4,024,246  shares of common
stock  acquired  from us and from  Mtel  Space  Technologies,  L.P.  and (2) the
beneficial owner of 812,500 shares issuable upon exercise of warrants we issued,
has exercised its piggyback  registration rights and is offering up to 4,836,746
shares of our common stock to the public.


                              PLAN OF DISTRIBUTION
                              --------------------

     The selling  stockholders may sell their shares of common stock,  from time
to time,  on the Nasdaq  National  Market (or any other  securities  exchange or
automated  quotation  system on which our shares are then listed or quoted or in
the  over-the-counter   market),  in  privately  negotiated  transactions  or  a
combination  of these  methods of sale.  The selling  stockholders  may sell the
shares at fixed prices (which may be changed),  at market  prices  prevailing at
the time of sale, at prices  related to market  prices or at negotiated  prices.
The selling  stockholders  may sell their common stock directly or by or through
agents,  brokers,  dealers or underwriters in one or more of the following types
of transactions:

     o    underwritten public offerings;

     o    ordinary  brokerage  transactions  and in  transactions  in which  the
          broker solicits purchasers;

     o    purchases  by  a  broker-dealer   as  principal  and  resale  by  such
          broker-dealer for its own account pursuant to this prospectus;

     o    for the purpose of covering short positions; and

     o    in "block" sales.


                                      -20-

<PAGE>


     If your purchase of shares from  Singapore  Telecom  under this  prospectus
results in you, together with any of your affiliates, holding in excess of 5% of
our  outstanding  common  stock,  you may be  required  to  become  a party to a
stockholders'  agreement,  amended and  restated as of December  31,  1993.  The
current parties to the stockholders' agreement include Singapore Telecom, Hughes
Communications  Satellite Services,  Inc., AT&T Wireless Services,  Inc. and the
Company.  The  stockholders'  agreement  includes  agreements  relating  to  the
governance of the Company,  the  ownership of our common  stock,  the voting and
transferability  of our  common  stock and other  matters.  For a more  complete
description   of  the  terms  of  the   stockholders'   agreement  see  "Selling
Stockholders - Singapore Telecom Has Material Relationships With Us."

     If a selling  stockholder  hires  brokers  or dealers to sell its shares of
common stock,  the selling  stockholder may arrange for other brokers or dealers
to  participate  in the  resales.  In  addition,  any  shares  covered  by  this
prospectus which qualify for sale pursuant to Section 4(1) of the Securities Act
of 1933 or Rule 144 may be sold under such  provisions  rather than  pursuant to
this prospectus.

     At the time a selling  stockholder  makes a particular  offer, that selling
stockholder,  if required,  will  distribute a prospectus  supplement  that sets
forth  the  number of shares of  common  stock  offered  and other  terms of the
offering,  including the name or names of any  underwriters,  dealers or agents,
the purchase price paid by any  underwriters for the common stock purchased from
the selling stockholder, any discounts,  commissions or other items constituting
compensation  from the selling  stockholde  and any  discounts,  concessions  or
commissions allowed or reallowed or paid to dealers.

     The selling stockholders and any brokers, dealers or agents who participate
in a sale of the shares of common stock may be considered  "underwriters" within
the meaning of Section 2(11) of the Securities Act. Any profits  realized by the
selling stockholders and the compensation of any brokers,  dealers or agents may
be deemed to be underwriting discounts and commissions.

     We have filed the  registration  statement of which this prospectus forms a
part with the SEC as required  pursuant to the terms of the registration  rights
agreements we have with each of the selling stockholders.

     Our outstanding  common stock is listed on the Nasdaq National Market,  and
we have applied for listing of the 11,357,278 shares of common stock that may be
offered and sold under this prospectus on the Nasdaq National Market.

     We will not receive any of the proceeds from the selling stockholders' sale
of our common  stock.  We will bear the costs of  registering  the shares of our
common stock held by the selling  stockholders,  including all  registration and
filing fees,  fees and expenses for compliance with securities or blue sky laws,
certain legal fees, printing expenses, messenger and delivery expenses, fees and
disbursements  of  custodians,  and fees and  disbursements  of counsel  for the
Company  and all  independent  certified  public  accountants  and  underwriters
(excluding discounts and commissions).

     Pursuant to the terms of the  registration  rights agreement with Motorola,
the  Company  and  Motorola  have  agreed to  indemnify  each other for  certain
liabilities,  including liabilities under the Securities Act, in connection with
the registration of the shares held by Motorola. Likewise, pursuant to the terms
of the  amended  and  restated  registration  rights  agreement  with  Singapore
Telecom,  the Company and Singapore  Telecom have agreed to indemnify each other
for certain  liabilities,  including  liabilities  under the Securities  Act, in
connection with the registration of the shares held by Singapore Telecom.


                          DESCRIPTION OF CAPITAL STOCK
                          ----------------------------

     Our authorized capital stock consists of 75,000,000 shares of common stock,
par value $0.01 per share and 200,000 shares of preferred stock, par value $0.01
per share.

Common Stock
- ------------

     On  February  26,  1999,  there  were  32,237,078  shares of  common  stock
outstanding, held of record by 275 stockholders.

     The holders of common stock are entitled to one vote for each share held of
record on all matters submitted to a vote of the stockholders. Cumulative voting
applies  to the  election  of  directors.  Subject  to  preferences  that may be
applicable to any then-outstanding  preferred stock, holders of common stock are
entitled to receive  ratably  such  dividends as may be declared by the Board of
Directors  out of  legally  available  funds.  In the  event  of a  liquidation,
dissolution  or  winding-up  of the  Company,  holders of the  common  stock are
entitled to share ratably in all assets  remaining  after we pay our liabilities
and the liquidation preference of any then-outstanding preferred stock. With two
exceptions,  there are no preemptive,  subscription,  redemption or sinking fund
provisions  applicable  to  the  common  stock.  The  two  exceptions  are:  (1)
provisions  of the  preferred  stock  described  below and (2)  provisions of an
existing  stockholders'  agreement as to  redemption if alien  ownership  issues
arise.  All  outstanding  shares of common  stock are,  and all shares of common
stock to be outstanding upon completion of the offering will be,  fully-paid and
nonassessable.

     Our  Certificate  of  Incorporation  requires  cumulative  voting  for  the
election of directors.  Under cumulative voting, each stockholder is entitled to
cast as many  votes in the  election  as equals  the  product  of the  number of
directors to be elected and the aggregate  number of shares of common stock held
by such  stockholder.  The  stockholder  may cumulate such votes for one or more
directors as the stockholder  determines.  Under cumulative voting,  assuming 10
directors  were  to be  elected  and  32,237,07  shares  of  common  stock  were
outstanding,  a  stockholder  would  have to hold at least  2,930,643  shares of
common stock to be certain of electing one director.

Preferred Stock
- ---------------

     The Board of Directors may issue  preferred stock in one or more series and
may fix the  designations,  preferences,  powers  and  relative,  participating,
optional and other rights,  qualifications,  limitations and restrictions on the
preferred stock,  including the dividend rate, conversion rights, voting rights,
redemption price and liquidation preference, and may fix the number of shares to
be  included  in any such  series.  Any  preferred  stock may rank senior to the
common  stock  for  the  payment  of  dividends  or  amounts  upon  liquidation,
dissolution or winding-up,  or both. In addition,  any shares of preferred stock
may have class or series voting  rights.  We do not have any shares of preferred
stock  outstanding.  Issuances  of  preferred  stock,  while  providing  us with
flexibility  in connection  with general  corporate  purposes,  may, among other
things,  have an adverse  effect on the rights of holders of common  stock.  The
Board of Directors, without stockholder approval, can issue preferred stock with
voting and conversion  rights that could  adversely  affect the voting power and
other rights of holders of common  stock.  Preferred  stock could thus be issued
quickly  with  terms  calculated  to delay or prevent a change of control of the
Company  or to make  the  removal  of  management  more  difficult.  In  certain
circumstances,  this could have the effect of decreasing the market price of the
common stock.

Certain Provisions of the Company's Certificate of Incorporation and Bylaws
- ---------------------------------------------------------------------------

     Certificate of  Incorporation.  As currently in effect,  our Certificate of
     ------------------------------
Incorporation  may not be amended,  modified,  rendered  ineffective or repealed
except by the vote of the holders of  two-thirds  of the issued and  outstanding
shares of common  stock.  Except as required by law,  other classes or series of
stock will not be entitled to vote on any such amendment,  modification or other
change, unless and to the extent required by any applicable law. Our Certificate
of  Incorporation  currently  requires  the  affirmative  vote of the holders of
two-thirds of the issued and outstanding shares of common stock to approve:

     o    our merger or consolidation with or into any other entity;

     o    our dissolution or liquidation; or

     o    the  sale,  exchange  or  lease  of  all or  substantially  all of our
          property and assets.

     The  Certificate  of  Incorporation  also requires that at each election of
directors by the holders of common stock, all directors must be elected.

     Bylaws.  As  currently  in  effect,  our  Bylaws  require  that there be 10
     -------
directors on the Board of Directors. The Bylaws provide that special meetings of
the stockholders generally may be called by the president and shall be called at
the request of the holders of at least one-third of the common stock then issued
and outstanding.  A special meeting solely to elect all directors of the Company
shall be called at the  written  request of a holder or  holders  of  sufficient
shares of common stock to then elect at least one director  under  principles of
cumulative  voting.  The Bylaws  also  provide  that  except as  provided in the
Certificate of Incorporation or the Bylaws,  the Bylaws may be altered,  amended
or repealed or new Bylaws may be adopted only upon the vote of either:

     o    three-fourths of the members of the Board of Directors then in office;
          or

     o    the  holders of  two-thirds  of the issued and  outstanding  shares of
          common stock.

Warrants Issued In Connection with Debt Offering
- ------------------------------------------------

     We issued 335,000  Warrants  pursuant to the warrant  agreement dated March
31,  1998 in a private  transaction  that was not  subject  to the  registration
requirements of the Securities Act. Each Warrant,  when exercised by its holder,
will entitle the holder to receive 3.75749 fully paid and non-assessable  shares
of our common stock at an exercise price of $12.51 per share. The exercise price
and the number of shares of common stock issuable upon exercise of a Warrant are
both subject to adjustment.

     The Warrants became  exercisable on June 26, 1998.  Unless  exercised,  the
Warrants will expire on April 1, 2008.  The Warrants  entitle the holders of the
Warrants to purchase,  in the  aggregate,  approximately  3% of our  outstanding
common  stock  on a  fully-diluted  basis  as of the  date  of  issuance  of the
Warrants,  after giving effect to the exercise of all  in-the-money  outstanding
options and rights we have issued.  We will give notice of  expiration  not less
than 90 nor more than 120 days prior to the  expiration  date to the  registered
holders of the then outstanding  Warrants.  If we fail to give this notice,  the
Warrants  will not expire until 90 days after we give  notice.  In no event will
holders  be  entitled  to any  damages or other  remedy for our  failure to give
notice, other than this extension.


                                  LEGAL MATTERS
                                  -------------

     Certain legal matters with respect to the shares of common stock offered by
this prospectus  will be passed upon for the Company by Randy Segal,  our Senior
Vice President,  General Counsel and Secretary. Ms. Segal owns 156,841 shares of
common  stock.  Ms.  Segal's  ownership  includes  shares she owns  through  our
matching  401(k) Plan and/or  Employee  Stock  Purchase Plan. Her ownership also
includes  shares  issuable upon the exercise of options  granted under the Stock
Option Plan which options are veste and exercisable,  subject to compliance with
applicable securities laws.


                                     EXPERTS
                                     -------

     The  consolidated   financial   statements  of  American  Mobile  Satellite
Corporation  as of  December  31, 1997 and 1998 and for each of the years in the
three-year  period ended  December 31, 1998,  incorporated  by reference in this
registration  statement,  have been audited by Arthur Andersen LLP,  independent
public accountants,  as indicated in their report with respect thereto,  and are
incorporated by reference  herein in reliance upon the authority of said firm as
experts in giving said  report.  The  consolidated  financial  statements  of XM
Satellite  Radio Holdings Inc. (a development  stage Company) as of December 31,
1998 and 1997, for the years ended December 31, 1998 and 1997 and for the period
from December 15, 1992 (date of inception)  through December 31, 1998, have been
incorporated by reference herein and in the  registration  statement in reliance
upon  the  report  of  KPMG  LLP,  independent   certified  public  accountants,
incorporated by reference herein, and upon the authority of said firm as experts
in  accounting  and  auditing.  The report of KPMG LLP covering the December 31,
1998  consolidated  financial  statements  of XM Satellite  Radio  Holdings Inc.
contains an explanatory paragraph that states that the Company has not commenced
operations,  has negative  working capital of $130,341,000 and is dependent upon
debt and equity  financings which raise  substantial  doubt about its ability to
continue  as a going  concern.  The  consolidated  financial  statements  do not
include any adjustments that might result from the outcome of that uncertainty.


                       WHERE YOU CAN FIND MORE INFORMATION
                       -----------------------------------

     We file annual,  quarterly and special reports,  proxy statements and other
information  with the SEC.  You may  read and copy any  document  we file at the
SEC's  public  reference  rooms in  Washington,  D.C.,  New  York,  New York and
Chicago, Illinois. Please call the SEC at 1-800-SEC-0330 for further information
on the public  reference rooms. Our SEC filings are also available to the public
at the SEC's web site at http://www.sec.gov. You also may find information about
us on our web site at http://www.ammobile.com.

     The SEC allows us to incorporate by reference the information  that we file
with the SEC, which means that we can disclose  important  information to you by
referring you to those documents.  The information  incorporated by reference is
considered to be part of this  prospectus,  and  information  that we file later
with the SEC will  automatically  update  and  supersede  this  information.  We
incorporate 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; and

     b. the  description  of  our  capital  stock  contained in our registration
        statement on Form 8-A, dated December 9, 1993  and  on Form 8-A/A, dated
        December 13, 1993.

     You may  request  a copy of  these  filings,  at no  cost,  by  writing  or
telephoning us 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) 758-6130

     No  person  has  been  authorized  to give any  information  or to make any
representation  other than those contained in this prospectus in connection with
the offering of common stock.  If  information or  representations  are given or
made you must not rely on it as if we  authorized  it.  Neither the  delivery of
this  prospectus nor any sale made  hereunder  shall,  under any  circumstances,
create  an  implication  that  the  information  contained  or  incorporated  by
reference  herein is correct as of any time subsequent to its date or that there
has  been no  change  in the  affairs  of the  Company  since  such  date.  This
prospectus does not constitute an offer to sell or a solicitation of an offer to
buy any  securities  offered hereby in any  jurisdiction  in which such offer or
solicitation  is not  permitted,  or to anyone  whom it is unlawful to make such
offer or solicitation.







<PAGE>






                                     PART II
                                     -------

                     INFORMATION NOT REQUIRED IN PROSPECTUS
                     --------------------------------------

ITEM 14.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.
- --------  --------------------------------------------

     The following are the estimated expenses (other than underwriting discounts
and  commissions)  of the  issuance and  distribution  of the  securities  being
registered to be paid by the Company.

     SEC registration fee.................................        $19,887
     Legal fees and expenses..............................         60,600
     Blue Sky fees and expenses...........................          4,400
     Accounting fees and expenses.........................         30,000
     Listing fees.........................................         17,500
     Miscellaneous........................................         10,000
                                                                  -------
      Total                                                      $142,387

ITEM 15.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
- --------  ------------------------------------------

     The Company's  Bylaws provide that the Company will indemnify its directors
and officers to the fullest extent permitted by Delaware law. The Company may be
required to advance  litigation  expenses in the case of stockholder  derivative
actions or other actions,  against an undertaking  by the  indemnified  party to
repay such advances if it is ultimately determined that the indemnified party is
not entitled to indemnification.

     In addition,  the Company's  Certificate  of  Incorporation  provides that,
pursuant to Delaware law, its directors shall not be liable for monetary damages
for breach of the directors'  fiduciary duty of care to the  corporation and its
stockholders.  This  provision  in the  Certificate  of  Incorporation  does not
eliminate the duty of care, and in appropriate  circumstances equitable remedies
such as injunctive or other forms of  nonmonetary  relief will remain  available
under  Delaware  law. In addition,  eac director  will continue to be subject to
liability for breach of the  director's  duty of loyalty to the Company for acts
or omissions not in good faith or involving intentional misconduct,  for knowing
violations  of law,  for  actions  leading to improper  personal  benefit to the
director,  and for payment of  dividends  or approval  of stock  repurchases  or
redemptions  that are unlawful  under  Delaware law. The provision also does not
affect a director's  responsibilities  under any other law,  such as the federal
securities laws.

     At present,  there is no pending  litigation  or  proceeding  involving  an
officer or director of the Company as to which  indemnification is being sought,
nor is the Company aware of any threatened  litigation that may result in claims
for indemnification by any officer or director.


                                      II-1


<PAGE>





ITEM 16.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.
- --------  -------------------------------------------

Exhibits
- --------

5.1  Opinion  of  Randy  Segal,  General  Counsel,  Senior  Vice  President  and
     Secretary.*

5.2  Opinion  of  Randy  Segal,  General  Counsel,  Senior  Vice  President  and
     Secretary.

23.1 Consent of Arthur Andersen LLP, independent public accountants.

23.2 Consent of KPMG LLP, independent public accountants.

23.3 Consent  of  Randy  Segal,  General  Counsel,  Senior  Vice  President  and
     Secretary (included in Exhibit 5.1 to this registration statement).*

23.4 Consent  of  Randy  Segal,  General  Counsel,  Senior  Vice  President  and
     Secretary (included in Exhibit 5.2 to this registration statement).

24   Powers of Attorney of certain directors and officers of the Company.*

24.1 Power of Attorney of W. Bartlett Snell. 

- ---------- 
* Previously filed.


ITEM 17.  UNDERTAKINGS.
- --------  -------------

(a)  The undersigned registrant hereby undertakes:

     (1)  To file,  during any period in which offers or sales are being made, a
          post-effective amendment to this Registration Statement:

          (i)       To include any  prospectus  required by section  10(a)(3) of
                    the Securities Act of 1933;
          (ii)      To reflect  in the  prospectus  any facts or events  arising
                    after the effective date of the  Registration  Statement (or
                    the most recent  post-effective  amendment  thereof)  which,
                    individually  or in the  aggregate,  represent a fundamental
                    change  in the  information  set  forth in the  Registration
                    Statement.  Notwithstanding  the foregoing,  any increase or
                    decrease  in  volume  of  securities  offered  (if the total
                    dollar  value of  securities  offered  would not exceed that
                    which was registered) and any deviation from the low or high
                    end of the estimated maximum offering range may be reflected
                    in the form of prospectus filed with the Commission pursuant
                    to Rule 424(b) of the  Securities  Act if, in the aggregate,
                    the changes in volume and price represent no more than a 20%
                    change in the maximum aggregate  offering price set forth in
                    the "Calculation of Registration Fee" table in the effective
                    Registration   Statement;   
          (iii)     To include any material information with respect to the plan
                    of distribution not previously disclosed in the Registration
                    Statement or any material change to such  information in the
                    Registration Statement;  Provided,  however, that paragraphs
                    (a)(1)(i)  and  (a)(1)(ii)  do not apply if the  information


                                      II-2

<PAGE>
                    required  to be included in a  post-effective  amendment  by
                    those  paragraphs is contained in periodic  reports filed by
                    the  registrant  pursuant to Section 13 or Section  15(d) of
                    the Securities Exchange Act of 1934 that are incorporated by
                    reference in the Registration Statement. 

     (2)  That,  for  the  purpose  of  determining   any  liability  under  the
          Securities Act of 1933,  each such  post-effective  amendment shall be
          deemed to be a new registration  statement  relating to the securities
          offered  therein,  and the  offering of such  securities  at that time
          shall be deemed to be the initial bona fide offering thereof.

     (3)  To remove from registration by means of a post-effective amendment any
          of  the  securities  being  registered  which  remain  unsold  at  the
          termination of the offering.

(b)  The  undersigned   registrant  hereby  undertakes  that,  for  purposes  of
     determining  any liability under the Securities Act of 1933, each filing of
     the  registrant's  annual report pursuant to Section 13(a) or Section 15(d)
     of the Securities Exchange Act of 1934 (and, where applicable,  each filing
     of an employee  benefit  plan's annual report  pursuant to Section 15(d) of
     the Securities  Exchange Act of 1934) that is  incorporated by reference in
     the  Registration  Statement  shall  be  deemed  to be a  new  registration
     statement relating to the securities  offered therein,  and the offering of
     such  securities  at that time shall be deemed to be the initial  bona fide
     offering thereof.

(c)  Insofar as indemnification for liabilities arising under the Securities Act
     of 1933 may be permitted to directors,  officers and controlling persons of
     the  registrant  pursuant to the foregoing  provisions,  or otherwise,  the
     registrant  has been  advised  that in the  opinion of the  Securities  and
     Exchange  Commission  such  indemnification  is  against  public  policy as
     expressed in the Act and is, therefore,  unenforceable. In the event that a
     claim for  indemnification  against such liabilities (other than th payment
     by the  registrant of expenses  incurred or paid by a director,  officer or
     controlling  person of the  registrant  in the  successful  defense  of any
     action,  suit or  proceeding)  is  asserted  by such  director,  officer or
     controlling person in connection with the securities being registered,  the
     registrant  will,  unless in the opinion of its counsel the matter has been
     settled  by  controlling  precedent,  submit  to  a  court  of  appropriate
     jurisdiction  the question  whether such  indemnification  by it is against
     public  policy as  expressed  in the Act and will be  governed by the final
     adjudication of such issue.


                                      II-3


<PAGE>





                                   SIGNATURES
                                   ----------

     Pursuant to the  requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for filing on Form S-3 and has duly caused this  amendment  to the
registration statement to be signed on its behalf by the undersigned,  thereunto
duly authorized in the County of Fairfax,  Commonwealth of Virginia, on the 30th
day of March, 1999.

                                AMERICAN MOBILE SATELLITE CORPORATION


                                By: /s/Walter V. Purnell, Jr.
                                Name:  Walter V. Purnell, Jr.
                                Title:     President and Chief Executive Officer

     Pursuant to the  requirements of the Securities Act of 1933, this amendment
to the Registration  Statement has been signed below by the following persons in
the capacities and on the dates indicated:

Signature                       Title                             Date

/s/ Walter V. Purnell, Jr.      President and Chief               March 30, 1999
- -----------------------------   Executive Officer, and Director
Walter V. Purnell, Jr.          (Principal Executive Officer)

/s/ W. Bartlett Snell           Senior Vice President and Chief   March 30, 1999
- -----------------------------   Financial Officer (Principal
W. Bartlett Snell               Financial and Accounting Officer)


/s/ Gary M. Parsons*            Chairman of the Board             March 30, 1999
- -----------------------------   of Directors
Gary M. Parsons                 

/s/ Douglas I. Brandon*         Director                          March 30, 1999
- -----------------------------
Douglas I. Brandon

/s/ Pradeep P. Kaul*            Director                          March 30, 1999
- -----------------------------
Pradeep P. Kaul

/s/ Billy J. Parrott*           Director                          March 30, 1999
- -----------------------------
Billy J. Parrott

/s/ Andrew A. Quartner*         Director                          March 30, 1999
- -----------------------------
Andrew A. Quartner

/s/ Jack A. Shaw*               Director                          March 30, 1999
- -----------------------------
Jack A. Shaw


                                      II-4

<PAGE>


/s/ Roderick M. Sherwood, III*  Director                          March 30, 1999
- ------------------------------
Roderick M. Sherwood, III

/s/ Michael T. Smith*           Director                          March 30, 1999
- ------------------------------
Michael T. Smith

*/s/ Randy S. Segal             Power of Attorney                 March 30, 1999
- ------------------------------





                                      II-5


<PAGE>



                                                March 30, 1999



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

Ladies and Gentlemen:

On January 29, 1999, I provided an opinion in connection  with the  Registration
Statement on Form S-3 (the  "Registration  Statement")  filed by American Mobile
Satellite  Corporation  (the "Company") on January 29, 1999, with the Securities
and Exchange  Commission (the "Commission") under the Securities Act of 1933, as
amended,  relating  to (i)  335,000  warrants  (the "High  Yield  Warrants")  to
purchase  shares of the Company's  common  stock,  par value $.01 per share (the
"Common Stock"), issued pursuant to the Warrant Agreement, dated as of March 31,
1998,  between  the  Company  and  State  Street  Bank and Trust  Company,  (ii)
1,258,759  shares of Common Stock (the "High Yield Warrant  Shares") that may be
issued  from time to time by the  Company  upon the  exercise  of the High Yield
Warrants,  and (iii) 6,520,532 shares of Common Stock (the "Motorola  Additional
Shares") that may be sold by Motorola,  Inc.,  currently held in connection with
the High  Yield  Warrants,  the High  Yield  Warrants  Shares  and the  Motorola
Additional Shares.

In connection  with the Amendment No. 1 to the  Registration  Statement filed by
the Company with the Commission on the date hereof, I am providing an opinion to
the Company  relating to the  following  additional  securities:  (i)  4,024,246
shares of our Common Stock  acquired by Singapore  Telecommunications  Ltd. (the
"Selling  Stockholder")  that were acquired from a 1993 private  placement and a
1993  conversion  by  the  Selling  Stockholder  of  certain  convertible  notes
previously  issued  by  the  Company  (collectively,  the  "  Singapore  Telecom
Additional Shares"), and (ii) 812,500 shares of our Common Stock issuable to the
Selling  Stockholder  pursuant to warrants held by the Selling  Stockholder (the
"Singapore  Telecom  Warrant  Shares").  At your request,  this opinion is being
furnished to you for filing as Exhibit 5.2 to the Registration Statement.

     In my capacity  as general  counsel of the  Company,  I have  examined  the
Certificate of Incorporation and Bylaws of the Company, each as amended to date,
the originals, or copies certified or otherwise identified, of corporate records
of the Company,  including minute books of the Company as furnished to me by the
Company, certificates of public officials and of representatives of the Company,
statutes  and  other  instruments  and  documents  as a basis  for the  opinions
hereinafter expressed.  In giving such opinions, I have relied upon certificates
of officers  of the  Company  with  respect to the  accuracy of certain  factual
matters contained in such certificates.

     On the basis of the foregoing, and subject to the assumptions,  limitations
and qualifications set forth herein, I am of the opinion that:

          o    The  Company  is a  corporation  duly  incorporated  and  validly
               existing under the laws of the State of Delaware.

          o    The Singapore Telecom Additional Shares to be sold by the Selling
               Stockholder are duly authorized,  validly issued,  fully paid and
               nonassessable.

          o    The issuance of the  Singapore  Telecom  Warrant  Shares has been
               duly authorized by all necessary  corporate action on the part of
               the Company,  and when the Singapore  Telecom  Warrant Shares are
               issued upon exercise of the warrants issued to Singapore  Telecom
               in accordance with the terms of such warrants  against payment of
               the consideration  therefor,  they will be validly issued,  fully
               paid and nonassessable.

     The  opinions  set forth above are  limited in all  respects to the General
Corporation law of the State of Delaware as in effect on the date hereof.

     I hereby  consent  to the  filing of this  opinion  as  Exhibit  5.2 to the
Registration Statement.


                                            Sincerely,

                                            /s/Randy S. Segal
                                            Randy S. Segal
                                            General Counsel








<PAGE>



                                                                    Exhibit 23.1



                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

As independent  public  accountants,  we hereby consent to the  incorporation by
reference in this registration statement on Form S-3/A of our report dated March
29, 1999 included in American Mobile Satellite  Corporation's  Form 10-K for the
year ended  December 31, 1998 and to all references to our Firm included in this
registration statement.

/s/  ARTHUR ANDERSEN LLP
Washington, D.C.
March 29, 1999






<PAGE>


                                                                    Exhibit 23.2
                          INDEPENDENT AUDITORS' CONSENT


The Board of Directors
XM Satellite Radio Holdings Inc.:

We consent to the incorporation by reference in this  registration  statement on
Form S-3 of American Mobile  Satellite  Corporation of our report dated February
12,  1999,  with  respect to the  consolidated  balance  sheets of XM  Satellite
Holdings Inc. and  Subsidiary (a  development  stage company) as of December 31,
1998  and  1997  and  the  related   consolidated   statements  of   operations,
stockholders'  equity and cash flows for the years ended  December  31, 1998 and
1997 and for the period from  December 15, 1992 (date of  inception) to December
31, 1998 which  report  appears in the  December  31, 1998 Form 10-K of American
Mobile Satellite Corporation dated March 30, 1999.

Our report,  dated  February 12, 1999,  contains an  explanatory  paragraph that
states that the Company  has not  commenced  operations,  has  negative  working
capital of $130,341,000  and is dependent upon debt and equity  financings which
raise  substantial  doubt about its ability to continue as a going concern.  The
consolidated  financial  statements  do not include any  adjustments  that might
result from the outcome of that uncertainty.

                                                                    /s/ KPMG LLP

McLean, Virginia
March 30, 1999





                                                                    Exhibit 24.1



                                POWER OF ATTORNEY



     KNOW ALL MEN BY THESE PRESENTS,  that W. Bartlett Snell hereby  constitutes
and  appoints  Walter V.  Purnell,  Jr. and Randy S. Segal,  his true and lawful
attorney-in-fact  and agent, with full power of substitution and resubstitution,
for him and in his name,  place,  and stead, in any and all capacities,  to sign
any and all  amendments to this  registration  statement,  and to file the same,
with exhibits  thereto,  and other  documents in connection  therewith  with the
Securities  and Exchange  Commission,  granting unto said  attorney-in-fact  and
agent full power and  authority  to do and perform  each and every act and thing
requisite  and necessary to be done, as fully to all and intents and purposes as
he might or could do in person,  hereby  ratifying and  confirming all that said
attorney-in-fact  and  agent or either of them,  or their or his  substitute  or
substitutes, may lawfully do or cause to be done by virtue hereof.


     IN WITNESS WHEREOF,  the undersigned has cause this Power of Attorney to be
executed as of this 30th day of March, 1999.

                                              /s/ W. Bartlett Snell
                                              W. Bartlett Snell
                                              Senior Vice President and
                                              Chief Financial Officer









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