AMERICAN MOBILE SATELLITE CORP
S-3, 1999-01-29
COMMUNICATIONS SERVICES, NEC
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                                            Registration No. 333-______


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    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
                            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(1)              price(1)
- -----------------------------------------------------------------------------------------------------
<S>                       <C>              <C>                <C>                 <C>
Warrants to
purchase Common
Stock                        335,000           N/A(1)                N/A(1)                N/A(1)
Common Stock,
$0.01 par value per
share (2)                  1,258,759          $12.51(3)       $15,747,075(3)           $4,378
Common Stock,
$0.01 par value per
share (4)                  6,520,532            (5)           $33,825,259(5)           $9,404
=====================     ===========      =============      =================   ==============
</TABLE>

(1)  In accordance with Rule 457(g) under the Securities Act of 1933, as amended
     (the "Securities Act"), no separate  registration fee is payable in respect
     of the warrants  ("Warrants") to purchase shares of common stock, par value
     $.01 per share ("Common Stock").
(2)  Represents  the  shares  of  Common Stock issuable upon the exercise of the
     Warrants.  
(3)  Estimated in  accordance  with Rule 457(g) under the  Securities  Act
     solely for the purpose of computing
     the amount of the registration fee.
(4)  Represents shares of Common Stock that may be sold by certain  stockholders
     of the Company.  
(5)  Estimated  in  accordance  with Rule 457(c) 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  ($5.1875) as reported on
the Nasdaq National Market on January 28, 1999.


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.



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


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

     This Registration Statement contains two forms of prospectus: (1) one to 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 other in connection  with offers and sales of shares of Common Stock
held  by  Motorola,  a  stockholder  of  the  Company.  The  sections  in  these
prospectuses  relating to general  statements  about the Company,  as opposed to
statements about the securities covered thereby, are identical.






<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 February __, 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 are offering and
selling 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.








<PAGE>







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

Prospectus Summary.............................................................2
         The Company...........................................................2
         The Offering..........................................................3
Risk Factors...................................................................5
Use of Proceeds...............................................................18
Selling Warrantholders........................................................18
Plan of Distribution..........................................................22
Description of the Warrants...................................................23
Description of Capital Stock..................................................28
Legal Matters.................................................................30
Experts.......................................................................30
Where You Can Find More Information...........................................31






     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."


                                      - 1 -


<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 the mobile
satellite  services  license  to a  consortium  of  all  willing  and  qualified
applicants.  The Company was formed by eight of the initial  applicants  for the
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  ("DARK")  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 an equity interest 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  terrestrial  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  335,000 Warrants and 1,258,759
                                shares of our common  stock  issuable  upon  the
                                exercise of the Warrants.  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 nine months
ended September 30, 1998, we reported  operating losses of  approximately  $65.6
million.  For historical  periods prior to our acquisition of ARDIS, we reported
operating  losses of  approximately  $97.4  million,  $120.0  million  and $70.5
million in 1997,  1996 and 1995.  During these periods ARDIS reported  operating
losses of approximately $17.4 million, $29.2 million, and $40.6 million in 1997,
1996 and 1995. We expect to have  significant  operating  losses and will record
significant net cash outflow in the near term. 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 or our marketing efforts will be successful.

     The leasing of our  satellite to a third party has been delayed and may not
materialize.  Accordingly,  we are considering other  alternatives for increased
usage from third  parties.  Without  increased  utilization,  future  cash flows
generated by the satellite and its network  components  may not be sufficient to
cover the  carrying  value  and  accordingly,  a write  down of the value of the
assets might be necessary.

     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 September  30, 1998,  our  indebtedness  totaled  approximately  $492
million ($484 million net of debt discount). As of September 30, 1998 we had $63
million  available  under AMSC  Acquisition  Company,  Inc.'s  revolving  credit
facility;  however,  the ability to borrow under this  facility is subject to us
meeting certain covenants which we may not meet in the future.  AMSC Acquisition

                                      - 5 -


<PAGE>

also  received a  commitment  from  Motorola  for up to $10.0  million of vendor
financing of 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 $114.1  million for the nine
months ended September 30, 1998. At September 30, 1998 our stockholders'  equity
was  approximately  $10.6 million.  We and our subsidiaries will be permitted to
incur additional indebtedness in the future.

     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 interest expense,  capital  expenditures and working capital.  We
will continue this practice  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  7.0% 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 October 31, 1998, we had borrowed  $591,707 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 the 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


                                      - 7 -


<PAGE>





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 finance 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 that 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.




                                      - 8 -


<PAGE>

We May Be Subject to Liability Under the ARDIS/UPS Contract
- -----------------------------------------------------------

         Our wholly-owned,  indirect subsidiary,  ARDIS, entered into a contract
with UPS for the use of the ARDIS network.  Under this  contract,  we anticipate
providing  communication  services to UPS for approximately  50,000  terrestrial
wireless  data  units by the end of 2001.  However,  performance  under  the UPS
Contract is subject to certain significant conditions, including, among others:

         o  required  capital  expenditures  to  expand  capacity  of  the ARDIS
            network in certain areas;

         o  successful development of the DIAD III wireless data terminal device
            by Motorola; and

         o  successful  deployment  of the DIAD III devices on the ARDIS network
            within strict network  operational  performance levels guaranteed by
            ARDIS.

     The UPS  Contract  will require  capital  spending of  approximately  $10.5
million  over the next three  years.  In  addition,  the  contract  represents a
significant  implementation  effort  of a  magnitude  in  excess  of that of any
existing ARDIS customer. Failure to meet the requirements under the UPS Contract
could result in a loss of the contract as well as monetary  penalties that could
materially adversely affect our business.

     Under the UPS Contract, we also have significant warranties of performance,
both during the implementation phase and for ongoing network performance. During
the   implementation   phase,  we  must  meet  key  checkpoints  and  milestones
culminating in an acceptance test.  Failure of the acceptance test could result,
after a cure period, in the loss of the contract.  In addition,  we will have to
construct  network  capacity  in several key  cities.  Failure to complete  such
construction by the committed dates would subject us to monthly  penalties until
we achieve compliance.

     On an ongoing basis,  the UPS Contract  requires that we guarantee  network
performance levels. If network  availability drops below 99%, we will be subject
to an  initial  penalty  of 2% of  the  average  monthly  use  of  the  service,
calculated  as the average of the last three  months in the affected  area.  The
penalty increases if performance levels further drop.

     As a part of the  negotiations  leading to the signing of the UPS Contract,
Motorola issued a performance guarantee regarding the network's performance.  In
connection  with our  acquisition of ARDIS,  we agreed to indemnify  Motorola in
connection   with  such   performance   guarantee,   and  as  security  for  our
indemnification  obligations  we have  deposited  $10.0  million  into an escrow
account.  This escrow  account has the same  three-year  term (with two possible
one-year renewals) as the UPS Contract.

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

     After  accounting for the acquisition of ARDIS,  three customers  accounted
for an aggregate  of 32% of our  recurring  service  revenue for the nine months
ended September 30, 1998 as follows:


       o  IBM -- 20%;

       o  NCR -- 7%; and

       o  Pitney Bowes -- 5%.

                                      - 9 -


<PAGE>


     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.

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.

                                     - 10 -


<PAGE>


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. Also, in constructing  additional  network sites ARDIS may
encounter  interfering  facilities  operated  by other  licensees  that were not
anticipated in the design and licensing of the ARDIS  facilities.  To the extent
that ARDIS  encounters  such  interfering  facilities,  ARDIS may be required to
purchase  the  interfering   facilities  or  to  cease   operations  where  such
interference is encountered.

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, most recently with respect to MSAT-2 in January 1998. 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.  If a serious
malfunction were to occur at a time when we have no backup capacity, there would
be a material adverse effect on our business.

     MSAT-2 has an expected remaining service life of approximately  seven years
and MSAT-1 has an expected  remaining  service life of greater than seven years,
in each case 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 or MSAT-1.  It is also  possible that either  satellite  could be
damaged by  electromagnetic  storms or collisions  with other objects,  although
such occurrences are rare.  Although we believe that the actual service lives of
both  satellites may exceed their expected  service lives,  we cannot  guarantee
that the expected service life of either 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.

     If there is a failure of MSAT-2 and MSAT-1 is not available for back-up, we
would  have  several  additional  options to replace  the lost  capacity.  These
options include leasing or purchasing  capacity on certain Inmarsat  satellites,


                                     - 11 -


<PAGE>





or launching a new satellite.  Any one of these options might not be adequate to
maintain all current service offerings,  and would require substantial lead-time
and significant financing.  It is likely that there would be significant service
interruptions and it would be necessary to raise  significant  additional funds,
both of which could have a material adverse effect on our business.

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
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.


                                     - 12 -


<PAGE>






     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  International  Bureau  of  the  FCC  granted  an
application  for  Special  Temporary  Authority  to use TMI's  space  segment to
conduct  market tests in the U.S. for the next six months using up to 500 mobile
terminals.  We have asked the full  Commission  to review this decision and stay
the effectiveness of the temporary authorization. There can be no assurance that
the  FCC  will  stay  the   effectiveness   of  this  decision  or  rescind  the
International Bureau's grant of Special Temporary Authority.

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.  Under  the Year 2000  Readiness  Program,  we have
prioritized our core systems to undergo an assessment of Year 2000 vulnerability
and, if  necessary,  repair of Year 2000  problems.  Our core  business  systems
include both  hardware and software  systems whose failure could have a material
impact on our  financial  condition  and  results of  operations.  Vendors  that
provide  critical  products  and  services  to us  are  also  included  in  this
assessment of core business systems.  Although the core business systems are the
top priority in our Year 2000  Readiness  Program,  we are  assessing all of our
software and hardware for Year 2000 readiness.

     Our Year 2000 Readiness Program includes the following phases:

     Awareness Phase:
     ----------------

     o educating  employees  about the  problem and how the Year 2000  Readiness
       Program will be implemented.

     Inventory Phase:
     ----------------

     o  identifying  all software  programs  and  hardware  systems and business
        relationships with third parties.

     Assessment Phase:
     -----------------

     o contacting  the vendors of commercial off the shelf software and hardware
       regarding Year 2000 readiness;

                                     - 13 -


<PAGE>






     o contacting  business partners and service providers  regarding their Year
       2000 readiness status;

     o analyzing software source code if available to us; and

     o prioritizing  non-compliant  software and systems based on criticality to
       the business.

     Renovation Phase:
     -----------------

     o obtaining and installing  software  upgrades or patches for software that
       is not Year 2000 ready; and

     o replacing software or hardware that is not Year 2000 ready.

     Validation/Testing Phase:
     -------------------------

     o conducting testing of upgraded/repaired software and hardware systems.

     Implementation/Rollout Phase:
     -----------------------------

     o installing upgraded/repaired software and hardware systems;

     o conducting user training; and

     o updating documentation.


     We  completed  the  Inventory  Phase in August 1998 for all systems that we
use,  including  software and hardware.  We have also essentially  completed the
Assessment Phase and overall, we are in the Renovation Phase.  Planning has also
begun for the Validation/Testing Phase and the Implementation/Rollout Phase.

     We  anticipate  completing  the  Implementation/Rollout  Phase for all core
business  systems before the end of 1999.  Achieving Year 2000 readiness for our
satellite  voice network and  deploying  renovated  data  terminals to customers
before the end of fourth  quarter 1999 will be the most  difficult  tasks of the
Implementation/Rollout  Phase.  While  we  cannot  guarantee  that  we  will  be
successful in making all core  business  systems Year 2000 ready by December 31,
1999,  we  believe  we will  be able to  successfully  complete  the  Year  2000
Readiness Program on time.

     The total cost of our Year 2000 Readiness Program is estimated to have been
$2.4  million  for  1998.   Expenditures for the Year 2000 Readiness  Program in


                                     - 14 -


<PAGE>




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.  Other  modification  costs,  such as  hardware  purchases,  are being
treated as capital expenditures.

     The cost and date on which we  believe we will be Year 2000 ready are based
on our best  estimates.  We cannot  guarantee that we will achieve these results
and our actual results could differ materially from those anticipated.

     Some of our critical  business  systems  depend on a significant  number of
software  programs and on services provided by third parties that are not within
our control. Failure to achieve Year 2000 readiness within our critical business
systems could result in possible service outages, miscalculations or disruptions
of  operations  that  could  have a material  impact on our  business.  While we
believe we will be able to achieve Year 2000 readiness in a timely  manner,  the
schedule for the  Implementation/Rollout  Phase of several core business systems
extends to the third or fourth quarter 1999. Therefore,  we may not achieve Year
2000  readiness 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 already  have  certain  contingency  plans in place to minimize  service
interruptions and these contingency plans 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.  Some of our
systems that we already have in place are being  incorporated into our Year 2000
contingency  plan.  If it is  commercially  reasonable to do so, we will include
other redundant or alternative  sources of services in our Year 2000 contingency
planning efforts.

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


                                     - 15 -


<PAGE>





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.

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, delay 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.

                                     - 16 -


<PAGE>






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
and could impair our ability to raise  additional  capital in the future through
the sale of equity  securities.  After  giving  effect to the issuance of common
stock upon the exercise of the Warrants,  there will be approximately 33,495,707
million shares of common stock outstanding, approximately 21.1 million shares of
which will have been  registered  under the  Securities  Act.  The  majority  of
outstanding  shares  are  subject  to various  registration  rights  agreements,
lock-up agreements,  and shareholder  agreements.  In addition, we have reserved
approximately  7.5 million shares of common stock for issuance upon the exercise
of other  outstanding  warrants  and  pursuant  to  employee  benefit  and stock
incentive plans. 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 do expect  that the  Warrants  will be  eligible  for trading in the
PORTAL 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.



                                     - 17 -


<PAGE>




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

     We will not  receive any  proceeds  from the sale of the  Warrants.  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  January  15,  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.


                                     - 18 -


<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>  
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              *                      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
</TABLE>



                                     - 19 -


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

                                     - 20 -


<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.


                                     - 21 -


<PAGE>



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

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

     The Selling  Warrantholders  may,  from time to time,  sell the Warrants to
purchasers directly. 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 on which
       the Warrants may be listed or quoted at the time of sale;

     o sales in the over-the-counter market;

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

     o sales through the writing of options.


     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.


                                     - 22 -


<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  Commission,  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 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


                                     - 23 -


<PAGE>





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.

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 3.00% 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 the Warrant  certificates
to us 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 payment 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.

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.

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


                                     - 24 -


<PAGE>





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
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.

                                     - 25 -


<PAGE>






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
     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.

                                     - 26 -


<PAGE>






          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.

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


                                     - 27 -


<PAGE>





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  January  15,  1999,  there  were  32,236,948  shares  of  common  stock
outstanding, held of record by 274 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.

                                     - 28 -


<PAGE>






     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  32,236,948  shares  of  common  stock  were
outstanding,  a  stockholder  would  have to hold at least  2,930,632  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.

                                     - 29 -


<PAGE>






     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.



                                  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 Vice
President,  General  Counsel and  Secretary.  Ms. Segal owns  163,881  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, 1996 and 1997 and for each of the years in the
three-year  period ended  December 31, 1997,  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  combined  financial  statements  of ARDIS
Holding  Company as of  December  31, 1996 and 1997 and for each of the years in
the three-year period ended December 31, 1997, incorporated by reference in this
registration  statement,  have  been  audited  by KPMG 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,  previously known as
AMRC  Holdings,  Inc.) as of December 31, 1997 and for the period from  December
15,  1992  (date of  inception)  through  December  31,  1997,  incorporated  by
reference  in this  registration  statement,  have  been  audited  by KPMG  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.

                                     - 30 -


<PAGE>







                       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, 1997 and
        on  Form  10-K/A for  the year ended  December 31, 1997, filed April 15,
        1998;

     b. our  quarterly  reports on Form 10-Q for the  quarters  ended  March 31,
        1998, June 30, 1998 and September 30, 1998;

     c. our  current  reports on Form 8-K,  dated  January 5, 1998,  January 22,
        1998,  March 9,  1998,  April 15, 1998,  June 5, 1998,  October 9, 1998,
        October 29, 1998, January 5, 1999 and January 20, 1999 and on Form 8-K/A
        dated  January 13, 1998; and

     d. 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
                             Vice President, General
                              Counsel and Secretary
                      American Mobile Satellite Corporation
                              10802 Parkridge Blvd.
                           Reston, Virginia 20191-5416
                                 (703) 758-6130

                                     - 31 -


<PAGE>
                

     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.


                                     - 32 -


<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 February __, 1999
                                                                      Prospectus
                            AMERICAN MOBILE SATELLITE
                                   CORPORATION


                        6,520,532 Shares of Common Stock

     Under this  prospectus,  Motorola,  Inc. is offering and selling  6,520,532
shares of our  common  stock.  When we  acquired  Motorola's  subsidiary,  ARDIS
Company, in March 1998, Motorola received these shares as partial payment of the
purchase price.

     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 4 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.







<PAGE>






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

Prospectus Summary.............................................................2
         The Company...........................................................2
         The Offering..........................................................3
Risk Factors...................................................................4
Use of Proceeds...............................................................17
Selling Stockholder...........................................................17
Registration Rights of Selling Stockholder....................................18
Plan of Distribution..........................................................19
Description of Capital Stock..................................................20
Legal Matters.................................................................22
Experts.......................................................................23
Where You Can Find More Information...........................................23






     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."


                                      - 1 -


<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 the mobile
satellite  services  license  to a  consortium  of  all  willing  and  qualified
applicants.  The Company was formed by eight of the initial  applicants  for the
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 an equity interest 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  terrestrial  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....Motorola is offering 6,520,532 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  the shares of
                      common stock Motorola holds.  The  agreement also requires
                      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  for  a  period  of not less than 180
                      days.

Use of Proceeds.......We will not receive  any proceeds  from   Motorola's  sale
                      of  our common stock.

                                      - 3 -



<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 nine months
ended September 30, 1998, we reported  operating losses of  approximately  $65.6
million.  For historical  periods prior to our acquisition of ARDIS, we reported
operating  losses of  approximately  $97.4  million,  $120.0  million  and $70.5
million in 1997,  1996 and 1995.  During these periods ARDIS reported  operating
losses of approximately $17.4 million, $29.2 million, and $40.6 million in 1997,
1996 and 1995. We expect to have  significant  operating  losses and will record
significant net cash outflow in the near term. 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 or our marketing efforts will be successful.

     The leasing of our  satellite to a third party has been delayed and may not
materialize.  Accordingly,  we are considering other  alternatives for increased
usage from third  parties.  Without  increased  utilization,  future  cash flows
generated by the satellite and its network  components  may not be sufficient to
cover the  carrying  value  and  accordingly,  a write  down of the value of the
assets might be necessary.

     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 September  30, 1998,  our  indebtedness  totaled  approximately  $492
million ($484 million net of debt discount). As of September 30, 1998 we had $63


                                      - 4 -


<PAGE>


million  available  under AMSC  Acquisition  Company,  Inc.'s  revolving  credit
facility;  however,  the ability to borrow under this  facility is subject to us
meeting certain covenants which we may not meet in the future.  AMSC Acquisition
also  received a  commitment  from  Motorola  for up to $10.0  million of vendor
financing of 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 $114.1  million for the nine
months ended September 30, 1998. At September 30, 1998 our stockholders'  equity
was  approximately  $10.6 million.  We and our subsidiaries will be permitted to
incur additional indebtedness in the future.

     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 interest expense,  capital  expenditures and working capital.  We
will continue this practice  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


                                      - 5 -


<PAGE>




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  7.0% 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 October 31, 1998, we had borrowed  $591,707 from Motorola under this
loan.

     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 the 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


                                      - 6 -


<PAGE>




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 finance 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 that
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.




                                      - 7 -


<PAGE>





We May Be Subject To Liability Under The ARDIS/UPS Contract
- -----------------------------------------------------------

     Our wholly-owned,  indirect subsidiary, ARDIS, entered into a contract with
UPS for  the use of the  ARDIS  network.  Under  this  contract,  we  anticipate
providing  communication  services to UPS for approximately  50,000  terrestrial
wireless  data  units by the end of 2001.  However,  performance  under  the UPS
Contract is subject to certain significant conditions, including, among others:

     o required capital  expenditures to expand capacity of the ARDIS network in
       certain areas;

     o successful  development of the DIAD III wireless data terminal  device by
       Motorola; and

     o successful deployment of the DIAD III devices on the ARDIS network within
       strict network operational performance levels guaranteed by ARDIS.

     The UPS  Contract  will require  capital  spending of  approximately  $10.5
million  over the next three  years.  In  addition,  the  contract  represents a
significant  implementation  effort  of a  magnitude  in  excess  of that of any
existing ARDIS customer. Failure to meet the requirements under the UPS Contract
could result in a loss of the contract as well as monetary  penalties that could
materially adversely affect our business.

     Under the UPS Contract, we also have significant warranties of performance,
both during the implementation phase and for ongoing network performance. During
the   implementation   phase,  we  must  meet  key  checkpoints  and  milestones
culminating in an acceptance test.  Failure of the acceptance test could result,
after a cure period, in the loss of the contract.  In addition,  we will have to
construct  network  capacity  in several key  cities.  Failure to complete  such
construction by the committed dates would subject us to monthly  penalties until
we achieve compliance.

     On an ongoing basis,  the UPS Contract  requires that we guarantee  network
performance levels. If network  availability drops below 99%, we will be subject
to an  initial  penalty  of 2% of  the  average  monthly  use  of  the  service,
calculated  as the average of the last three  months in the affected  area.  The
penalty increases if performance levels further drop.

     As a part of the  negotiations  leading to the signing of the UPS Contract,
Motorola issued a performance guarantee regarding the network's performance.  In
connection  with our  acquisition of ARDIS,  we agreed to indemnify  Motorola in
connection   with  such   performance   guarantee,   and  as  security  for  our
indemnification  obligations  we have  deposited  $10.0  million  into an escrow
account.  This escrow  account has the same  three-year  term (with two possible
one-year renewals) as the UPS Contract.




                                      - 9 -


<PAGE>





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

     After  accounting for the acquisition of ARDIS,  three customers  accounted
for an aggregate  of 32% of our  recurring  service  revenue for the nine months
ended September 30, 1998 as follows:

     o IBM -- 20%;

     o NCR -- 7%; and

     o Pitney Bowes -- 5%.


     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.

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


                                      - 9 -


<PAGE>




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. Also, in constructing  additional  network sites ARDIS may
encounter  interfering  facilities  operated  by other  licensees  that were not
anticipated in the design and licensing of the ARDIS  facilities.  To the extent
that ARDIS  encounters  such  interfering  facilities,  ARDIS may be required to
purchase  the  interfering   facilities  or  to  cease   operations  where  such
interference is encountered.

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, most recently with respect to MSAT-2 in January 1998. 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.  If a serious
malfunction were to occur at a time when we have no backup capacity, there would
be a material adverse effect on our business.

     MSAT-2 has an expected remaining service life of approximately  seven years
and MSAT-1 has an expected  remaining  service life of greater than seven years,
in each case 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 or MSAT-1.  It is also  possible that either  satellite  could be
damaged by  electromagnetic  storms or collisions  with other objects,  although
such occurrences are rare.  Although we believe that the actual service lives of
both  satellites may exceed their expected  service lives,  we cannot  guarantee
that the expected service life of either 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


                                     - 10 -


<PAGE>




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.

     If there is a failure of MSAT-2 and MSAT-1 is not available for back-up, we
would  have  several  additional  options to replace  the lost  capacity.  These
options include leasing or purchasing  capacity on certain Inmarsat  satellites,
or launching a new satellite.  Any one of these options might not be adequate to
maintain all current service offerings,  and would require substantial lead-time
and significant financing.  It is likely that there would be significant service
interruptions and it would be necessary to raise  significant  additional funds,
both of which could have a material adverse effect on our business.

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
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


                                     - 11 -


<PAGE>




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  International  Bureau  of  the  FCC  granted  an
application  for  Special  Temporary  Authority  to use TMI's  space  segment to
conduct  market tests in the U.S. for the next six months using up to 500 mobile
terminals.  We have asked the full  Commission  to review this decision and stay
the effectiveness of the temporary authorization. There can be no assurance that
the  FCC  will  stay  the   effectiveness   of  this  decision  or  rescind  the
International Bureau's grant of Special Temporary Authority.

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.  Under  the Year 2000  Readiness  Program,  we have
prioritized our core systems to undergo an assessment of Year 2000 vulnerability
and, if  necessary,  repair of Year 2000  problems.  Our core  business  systems
include both  hardware and software  systems whose failure could have a material
impact on our  financial  condition  and  results of  operations.  Vendors  that
provide  critical  products  and  services  to us  are  also  included  in  this
assessment of core business systems.  Although the core business systems are the
top priority in our Year 2000  Readiness  Program,  we are  assessing all of our
software and hardware for Year 2000 readiness.

     Our Year 2000 Readiness Program includes the following phases:

     Awareness Phase:
     ----------------

     o educating  employees  about the  problem and how the Year 2000  Readiness
       Program will be implemented.

     Inventory Phase:
     ----------------

     o identifying  all  software  programs  and  hardware  systems and business
       relationships with third parties.

                                     - 12 -


<PAGE>





     Assessment Phase:
     -----------------

     o contacting  the vendors of commercial off the shelf software and hardware
regarding Year 2000 readiness;

     o contacting  business partners and service providers  regarding their Year
2000 readiness status;

     o analyzing software source code if available to us; and

     o prioritizing  non-compliant  software and systems based on criticality to
the business.

     Renovation Phase:
     -----------------

     o obtaining and installing  software  upgrades or patches for software that
       is not Year 2000 ready; and

     o replacing software or hardware that is not Year 2000 ready.

     Validation/Testing Phase:
     -------------------------

     o conducting testing of upgraded/repaired software and hardware systems.

     Implementation/Rollout Phase:
     -----------------------------

     o installing upgraded/repaired software and hardware systems;

     o conducting user training; and

     o updating documentation.

     We  completed  the  Inventory  Phase in August 1998 for all systems that we
use,  including  software and hardware.  We have also essentially  completed the
Assessment Phase and overall, we are in the Renovation Phase.  Planning has also
begun for the Validation/Testing Phase and the Implementation/Rollout Phase.

     We  anticipate  completing  the  Implementation/Rollout  Phase for all core
business  systems before the end of 1999.  Achieving Year 2000 readiness for our
satellite  voice network and  deploying  renovated  data  terminals to customers
before the end of fourth  quarter 1999 will be the most  difficult  tasks of the
Implementation/Rollout  Phase.  While  we  cannot  guarantee  that  we  will  be
successful in making all core  business  systems Year 2000 ready by December 31,
1999,  we  believe  we will  be able to  successfully  complete  the  Year  2000
Readiness Program on time.


                                     - 13 -


<PAGE>





     The total cost of our Year 2000 Readiness Program is estimated to have been
$2.4 million for 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.
Other  modification  costs,  such as hardware  purchases,  are being  treated as
capital expenditures.

     The cost and date on which we  believe we will be Year 2000 ready are based
on our best  estimates.  We cannot  guarantee that we will achieve these results
and our actual results could differ materially from those anticipated.

     Some of our critical  business  systems  depend on a significant  number of
software  programs and on services provided by third parties that are not within
our control. Failure to achieve Year 2000 readiness within our critical business
systems could result in possible service outages, miscalculations or disruptions
of  operations  that  could  have a material  impact on our  business.  While we
believe we will be able to achieve Year 2000 readiness in a timely  manner,  the
schedule for the  Implementation/Rollout  Phase of several core business systems
extends to the third or fourth quarter 1999. Therefore,  we may not achieve Year
2000  readiness 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 already  have  certain  contingency  plans in place to minimize  service
interruptions and these contingency plans 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.  Some of our
systems that we already have in place are being  incorporated into our Year 2000
contingency  plan.  If it is  commercially  reasonable to do so, we will include
other redundant or alternative  sources of services in our Year 2000 contingency
planning efforts.

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.





                                     - 14 -


<PAGE>





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.

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, delay 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.



                                     - 15 -


<PAGE>





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
and could impair our ability to raise  additional  capital in the future through
the sale of equity  securities.  We have  issued  335,000  Warrants in a private
transaction  that we are also registering  under the  registration  statement of
which this  prospectus  forms a part.  After  giving  effect to the  issuance of
common stock upon the exercise of the Warrants, and including the shares offered
by Motorola,  there will be  approximately  33,495,707  million shares of common
stock  outstanding,  approximately  21.1 million  shares of which will have been
registered  under the  Securities  Act. The majority of  outstanding  shares are
subject to various  registration  rights  agreements,  lock-up  agreements,  and
shareholder agreements.  In addition, we have reserved approximately 7.5 million
shares of common  stock for  issuance  upon the  exercise  of other  outstanding
warrants  and  pursuant  to  employee  benefit and stock  incentive  plans.  See
"Description of Capital Stock."

                                     - 16 -


<PAGE>



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

     We will not receive any proceeds from  Motorola's sale of our common stock.
Motorola will receive all of the proceeds from its sale of our common stock.

                               SELLING STOCKHOLDER
                               -------------------

     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.

     The following  table shows, as of January 15, 1999, the number of shares of
common  stock that  Motorola  beneficially  owned and the number of shares  that
Motorola may offer under this prospectus. We cannot provide you with an estimate
of the number of shares of common stock that  Motorola  will hold in the future.
This  information is unavailable  because Motorola may sell all, some or none of
its shares of common stock.  The table has been prepared based upon  information
furnished to us by or on behalf of Motorola.


                               Number of Shares(1)               Percent(2)
                               -------------------               ----------

Motorola, Inc.                      6,520,532                       20.2

- ------------
(1)  Reflects  beneficial  ownership  of shares of  common stock prior to giving
     affect to the sale of the shares offered in this prospectus.
(2)  Reflects  the  percentage  of  the  outstanding   shares  of  common  stock
     beneficially owned.

     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.  Motorola,
however, does have other material relationships with us.

     First,  in  connection  with our  acquisition  of ARDIS we  agreed  to give
Motorola  participation  rights  with  respect  to our  common  stock  under the
participation  rights  agreement  dated  December  31,  1997.  If any of  Hughes
Communications  Satellite Services,  Inc., Singapore  Telecommunications Ltd. or
AT&T Wireless  Services,  Inc.  wants to transfer its shares of our common stock
other  than in a Rule 144 or  public  stock  exchange  or  Nasdaq  Stock  Market
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 three  stockholders  with similar  notice and
participation rights if Motorola decides to transfer its interests in our common
stock.  Second, the participation  rights agreement and the registration  rights


                                     - 17 -


<PAGE>




agreement  with  Motorola,  dated March 31, 1998,  gives  Motorola  "demand" and
"piggyback"  registration rights as described below. See "Registration Rights Of
Selling Stockholder."

     Third,  Motorola  has  entered  into an  agreement  with  our  wholly-owned
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 with
our subsidiary AMSC Acquisition Company, Inc. has with UPS. Funds borrowed under
this loan  agreement have an interest rate equal to LIBOR plus 7.0% 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 October 31, 1998, we had borrowed  $591,707 from Motorola  under
this loan.


                   REGISTRATION RIGHTS OF SELLING STOCKHOLDER
                   ------------------------------------------

     When we  issued  shares  of our  common  stock to  Motorola  as part of the
purchase  price  for  ARDIS,  we  agreed  to  register  those  shares  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  provided both
"demand" and "piggyback" registration rights.

     At any time 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 rights agreement also requires 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 for a
period of not less than 180 days.

     The registration  statement to which this prospectus relates is being filed
pursuant  to the  requirements  of the  warrant  registration  rights  agreement
between us and the underwriters of our March 31, 1998 offering of 335,000 units.
Under that  agreement,  we are required to register under the Securities Act the
warrants issued as part of the units and  the underlying shares  of common stock

                                     - 18 -


<PAGE>





issuable  pursuant to the warrants.  This is not an  underwritten  registration.
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 all of its  6,520,532  shares of our common
stock to the public at the same time as the registration of the warrants and the
underlying shares is deemed effective under the Securities Act.


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

     Motorola  may sell its 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. Motorola 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.  Motorola may sell its 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.

     If Motorola  hires  brokers or dealers to sell its shares of common  stock,
Motorola 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 Motorola makes a particular offer, Motorola, 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  Motorola,  any  discounts,
commissions  or other items  constituting  compensation  from  Motorola  and any
discounts, concessions or commissions allowed or reallowed or paid to dealers.

     Motorola and any brokers,  dealers or agents who  participate  in a sale of
the shares of common stock may be considered  "underwriters"  within the meaning


                                     - 19 -


<PAGE>




of Section 2(11) of the Securities Act. Any profits realized by Motorola 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
agreement.

     Our outstanding  common stock is listed on the Nasdaq National Market,  and
we have  applied for  listing of the  6,520,532  shares of common  stock held by
Motorola on the Nasdaq National Market.

     We will not receive any of the proceeds from  Motorola's sale of our common
stock. We will bear the costs of registering the shares of our common stock held
by Motorola,  including all  registration and filing fees, fees and expenses for
compliance with securities or blue sky laws,  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).  Motorola,
however,  is responsible  for the fees and  disbursements  of its separate legal
counsel in connection with the registration.

     Pursuant to the terms of the registration rights agreement, 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.


                          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  January  15,  1999,  there  were  32,236,948  shares  of  common  stock
outstanding, held of record by 274 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


                                     - 20 -


<PAGE>




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  32,236,948  shares  of  common  stock  were
outstanding,  a  stockholder  would  have to hold at least  2,930,632  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.


                                     - 21 -


<PAGE>



     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 3.00% 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 Vice
President,  General  Counsel and  Secretary.  Ms. Segal owns  163,881  shares of
common  stock.  Ms.  Segal's  ownership  includes  shares she owns  through  our


                                     - 22 -


<PAGE>




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, 1996 and 1997 and for each of the years in the
three-year  period ended  December 31, 1997,  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  combined  financial  statements  of ARDIS
Holding  Company as of  December  31, 1996 and 1997 and for each of the years in
the three-year period ended December 31, 1997, incorporated by reference in this
registration  statement,  have  been  audited  by KPMG 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,  previously known as
AMRC  Holdings,  Inc.) as of December 31, 1997 and for the period from  December
15,  1992  (date of  inception)  through  December  31,  1997,  incorporated  by
reference  in this  registration  statement,  have  been  audited  by KPMG  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.


                       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:


                                     - 23 -


<PAGE>





     a.   our annual  report on Form 10-K for the year ended  December  31, 1997
          and on Form 10-K/A for the year ended  December 31, 1997,  filed April
          15, 1998;

     b.   our  quarterly  reports on Form 10-Q for the quarters  ended March 31,
          1998, June 30, 1998 and September 30, 1998;

     c.   our current  reports on Form 8-K,  dated January 5, 1998,  January 22,
          1998,  March 9, 1998,  April 15, 1998, June 5, 1998,  October 9, 1998,
          October  29,  1998,  January 5, 1999 and  January 20, 1999 and on Form
          8-K/A dated January 13, 1998; and

     d.   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
                             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.


                                     - 24 -


<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............................................... $13,781

     Legal fees and  expenses................................................. *

     Blue Sky fees and  expenses.............................................. *

     Accounting fees and  expenses............................................ *

     Transfer agent fees...................................................... *

     Listing fees.........................................................17,500

     Miscellaneous............................................................ *
                                                                      ----------

     Total                                                                    $*

 .........
[* To be filed by amendment.]


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,  each 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.


                                      II-1




<PAGE>






     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.


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

Exhibits
- --------

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

23.1 Consent of Arthur Andersen LLP, independent public accountants.

23.2 Consent of KPMG LLP, Chicago, Illinois, independent public accountants.

23.3 Consent of KPMG LLP, Washington, D.C., independent public accountants.*

23.4 Consent of Randy Segal,  General Counsel,  Vice President and Secretary
     (included in Exhibit 5 to this registration statement).

24   Powers of Attorney of directors  and officers of the Company  (included
     in the signature page).
- ----------
*To be filed by amendment.


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


                                      II-2


<PAGE>






                   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
                   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 the 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  registration
statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized in the County of Fairfax,  Commonwealth of Virginia,  on the 28th day
of January, 1999.

                                               AMERICAN MOBILE SATELLITE
                                               CORPORATION

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


                                POWER OF ATTORNEY
                                -----------------

     KNOW ALL MEN BY THESE PRESENTS,  that each person whose  signature  appears
below hereby  constitutes and appoints Gary M. Parsons,  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  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.

     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
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              January 28, 1999
- -----------------------------  Executive Officer, and Director
Walter V. Purnell, Jr.         (Principal Executive Officer)

/s/ Stephen D. Peck            Vice President and Chief         January 28, 1999
- -----------------------------  Financial Officer (Principal 
Stephen D. Peck                Financial and Accounting Officer)

/s/ Gary M. Parsons            Chairman of the Board            January 28, 1999
- -----------------------------  of Directors
Gary M. Parsons                

                                      II-4




<PAGE>






/s/ Douglas I. Brandon         Director                         January 28, 1999
- -----------------------------
Douglas I. Brandon

/s/ Pradeep P. Kaul            Director                         January 28, 1999
- -----------------------------
Pradeep P. Kaul

/s/ Billy J. Parrott           Director                         January 28, 1999
- -----------------------------
Billy J. Parrott

/s/ Andrew A. Quartner         Director                         January 28, 1999
- -----------------------------
Andrew A. Quartner

/s/ Jack A. Shaw               Director                         January 28, 1999
- -----------------------------
Jack A. Shaw

/s/ Roderick M. Sherwood, III  Director                         January 28, 1999
- -----------------------------
Roderick M. Sherwood, III

/s/ Michael T. Smith           Director                         January 28, 1999
- -----------------------------
Michael T. Smith



                                      II-5






                                                                       Exhibit 5



                     AMERICAN MOBILE SATELLITE CORPORATION


                                             January 29, 1999



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

Ladies and Gentlemen:

     As set forth in the Registration  Statement on Form S-3 (the  "Registration
Statement") filed by American Mobile Satellite Corporation (the "Company"), with
the  Securities  and Exchange  Commission  under the  Securities Act of 1933, as
amended, relating to (i) 335,000 warrants (the "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 (the
"Warrant  Agreement"),  between  the  Company  and State  Street  Bank and Trust
Company,  (ii) 1,258,759 shares of Common Stock (the "Warrant  Shares") that may
be issued from time to time by the Company  upon the  exercise of the  Warrants,
and (iii) 6,520,532 shares of Common Stock (the "Additional Shares") that may be
sold by Motorola,  Inc.  (the "Selling  Stockholder"),  certain legal matters in
connection with the Warrants,  the Warrants Shares and the Additional Shares are
being passed upon for the Company by me. At your request,  this opinion is being
furnished to you for filing as Exhibit 5 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:

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


<PAGE>


American Mobile Satellite Corporation
January 29, 1999
Page 2





     2.   The Warrants are duly authorized and validly issued in accordance with
          the terms of the Warrant Agreement.

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

     4.   The Additional  Shares to be sold by the Selling  Stockholder are duly
          authorized, 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 to the
Registration Statement.


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








                                                                    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 of our report dated March
31, 1998 included in American Mobile Satellite  Corporation's  Form 10-K for the
year ended  December 31, 1997 and to all references to our Firm included in this
registration statement.

/s/  ARTHUR ANDERSEN LLP
Washington, D.C.
January 28, 1999












                                                                    Exhibit 23.2


                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

The Board of Directors
American Mobile Satellite Corporation:

We consent to the  incorporation by reference into the American Mobile Satellite
Corporation  (AMSC)  Registration  Statement  on Form  S-3 of our  report  dated
February 13, 1998, with respect to the combined  balance sheets of ARDIS Holding
Company as of December 31, 1996 and 1997, and the related combined statements of
operations,  stockholders'  equity,  and cash flows for each of the years in the
three-year  period ended  December 31,  1997,  which report  appears in the AMSC
Current Report on Form 8-K dated April 15, 1998 and to the reference to our firm
under the heading "Experts" in the prospectus.

/s/  KPMG LLP
Chicago, Illinois
January 26, 1999







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