AMERICAN MOBILE SATELLITE CORP
S-3, 1999-08-03
COMMUNICATIONS SERVICES, NEC
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     As filed with the Securities and Exchange Commission on August 3, 1999

                                            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 Identification Number)
 of incorporation or organization)

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

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


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

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

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

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

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



<PAGE>









                         CALCULATION OF REGISTRATION FEE


<TABLE>
<CAPTION>

                                                        Proposed
   Title of each class                                  maximum                 Proposed
           of                                        offering price             maximum
    securities to be           Amount to be               per                  aggregate                  Amount of
       registered             registered (1)             share                  offering               Registration fee
                                                                                 price
<S>                           <C>                      <C>                  <C>                           <C>
Common Stock,
$0.01 par value per
share                         8,614,244                $18.75(2)            $161,517,075(2)               $44,901.75
</TABLE>

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

(2)  Estimated in accordance  with Rule 457(c) under the  Securities  Act solely
     for the purpose of computing the amount of the registration fee.


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.



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






<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 August 3, 1999


                                                                     Prospectus

                      AMERICAN MOBILE SATELLITE CORPORATION

                        8,614,244 Shares of Common Stock

     The persons  listed in this  Prospectus  under "Selling  Stockholders"  may
offer  and sell from  time to time up to a total of  8,614,244  shares of common
stock of  American  Mobile  Satellite  Corporation.  We issued the shares  being
offered under this Prospectus in private transactions to XM Ventures, a Maryland
Trust.  This Prospectus covers sales of shares by XM Ventures.  In addition,  XM
Ventures  may  distribute  shares it owns to the  people  who own  shares of, or
options,  warrants  or other  rights to  purchase  shares  of,  common  stock of
WorldSpace,  Inc. which is the beneficiary of XM Ventures.  If XM Ventures makes
such a  distribution,  we will supplement this Prospectus to name any additional
selling stockholders.

     We will not receive any proceeds from the sale of the shares by the selling
stockholders named in this Prospectus.

     Our common stock is listed on the Nasdaq Stock Market's National Market and
traded under the symbol "SKYC."

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

     See "Risk Factors" beginning on page 3 for a discussion of certain material
factors that you should  consider in connection with an investment in our common
stock.

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

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

                The date of this Prospectus is __________, 1999.







<PAGE>






                                TABLE OF CONTENTS
                                                                            Page

Risk Factors................................................................   3
American Mobile's Business................................................... 26
Use of Proceeds.............................................................. 28
Selling Stockholders......................................................... 28
Registration Rights of Selling Stockholders.................................. 30
Plan of Distribution......................................................... 31
Legal Matters................................................................ 32
Experts...................................................................... 33
Where You Can Find More Information.......................................... 33
Certain Information About this Prospectus.................................... 33




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



                                        2


<PAGE>






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

     You should  carefully  consider the risks  described below before making an
investment  decision.  The risks and  uncertainties  described below are not the
only ones we face.  Additional risks and uncertainties,  of which we are unaware
or that we  currently  think  are  immaterial,  may  also  impair  our  business
operations.  If  any  of the  following  risks  actually  occur,  our  business,
financial  condition  or results of  operations  could be  materially  adversely
affected. In such case, the trading price of our common stock could decline, and
you may lose all or part of your investment.

         In  addition  to the risks  described  below  which  relate to our core
wireless  business  and our  company  generally,  there  are  significant  risks
associated with our investment in XM Radio.  We describe these risks  separately
under the caption  "XM Radio's  business  involves  significant  risks and these
risks may impair the value of our investment in XM Radio."

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  our  satellite  and  terrestrial
networks  and the cost of  developing,  selling and  providing  our products and
services.  For the year ended  December 31,  1998,  on a pro forma basis for the
ARDIS acquisition,  we reported operating losses of approximately $93.4 million,
and for the  quarter  ended March 31,  1999,  we  reported  operating  losses of
approximately $25.5 million.  For historical periods prior to our acquisition of
ARDIS, we reported  operating losses of  approximately  $97.4 million and $120.0
million  in 1997 and  1996,  respectively.  During  these  same  periods,  ARDIS
reported operating losses of approximately  $17.4 million and $29.2 million.  In
addition,  XM Radio incurred  aggregate net losses of approximately $1.7 million
from its inception through December 31, 1997, and an additional $20.5 million in
the 15-month  period  ended March 31, 1999.  We expect XM Radio's net losses and
negative cash flow to continue.  See the discussion  under "-- XM Radio has made
significant  expenditures and incurred  significant losses to date and these are
expected to grow." We expect to continue to make significant  capital outlays to
fund interest expense,  capital expenditures and working capital before we begin
to generate  positive cash flow from  operations.  These outlays are expected to
continue for the foreseeable  future.  We expect to have  significant  operating
losses and will record significant net cash outflow in the near term. We believe
that our cash resources,  together with existing available  borrowings,  will be
sufficient to fund operating losses, capital expenditures,  working capital, and
scheduled  principal  and  interest  payments  on debt  through the time when we
expect to generate positive free cash flow. However, we cannot guarantee that we
will have sufficient resources to complete the expenditures  required to operate
our  business  or to  achieve  positive  free cash flow  within  the time  frame
contemplated by our current projections.

     Since our  inception,  we have been  engaged in  developing  our  business,
recruiting key management and technical  personnel,  raising capital to fund our
operations,  and  developing  our network.  We have  introduced a variety of new

                                        3


<PAGE>



products  and  services,  some of which  have  not  achieved  widespread  market
acceptance.  We expect to continue to launch new products and services,  some of
which will be  introduced  in new market  segments,  in order to  capitalize  on
emerging  trends in our  industry.  The launch of such new products or the entry
into new market segments may require us to spend additional capital, which could
cause us to  continue  to incur  significant  operating  losses.  Our ability to
generate  positive  free cash flow will depend upon,  among other  factors,  the
successful  marketing  of our  services,  including  new  services  such  as our
eLink(SM)  wireless two-way  messaging  service.  We cannot guarantee that these
efforts will be successful.

Our extension into new wireless markets involves risks
- ------------------------------------------------------

     In May 1999, we announced our eLink wireless  email  service,  which uses a
palm-sized device that combines two-way wireless email and personal  information
management  software.  We believe that this  service may  represent an important
growth  opportunity  for us.  However,  the  market  for this type of service is
relatively untested and, therefore, there is a risk that demand for this service
will not  increase as rapidly as we hope.  The  failure of this  service to gain
market  acceptance  in a  timely  manner  or at all or the  failure  to  achieve
significant  market  penetration  could harm our business.  Our eLink service is
expected  to compete  initially  with one major  competitor,  which has  already
launched its service. While we believe our eLink service has several competitive
advantages  over  existing  competitive  services,   our  competitors  may  have
substantially greater financial,  technical,  marketing, sales, distribution and
other  resources  than ours.  Also,  the eLink  service  represents an effort to
target  individual  customers and small groups in  corporations,  as well as the
larger business customers which presently represent the overwhelming majority of
our business. We intend to reach such customers primarily through resellers such
as SkyTel.  This distribution  strategy makes us substantially  dependent on the
efforts of such resellers,  and if such resellers fail to adequately promote our
service or otherwise perform their obligations to us, sales of the eLink service
may be less than expected. In addition, we have spent, and expect to continue to
spend,   significant   operating  expenses  and  capital   expenditures  on  the
development,  testing,  marketing, and distribution of the eLink service, and we
are  contractually  committed to purchase  substantial  quantities  of the eLink
device from the manufacturer, following successful product certification. If the
service  does  not  achieve  acceptable  levels  of  market  acceptance,   these
expenditures and commitments could depress our operating results. If the service
does achieve market acceptance, its success will depend, in part, on our ability
to maintain an adequate supply of devices for subscribers, which are supplied by
a third  party  vendor  over whom we have no  control.  The success of the eLink
service will also depend on our ability to continue to use,  promote and protect
the eLink service name and the other intellectual  property  associated with the
service.

We have substantial indebtedness, which may make our business more vulnerable
- -----------------------------------------------------------------------------

     As of March 31,  1999,  our total  indebtedness  was  approximately  $533.9
million,  and $526.2 million net of debt discount.  As of March 31, 1999, we had
$41.0 million  available  under our revolving  credit  facility and $5.1 million
available under an equipment  financing  facility from Motorola.  On a pro forma
basis, after giving effect to the acquisition of ARDIS and the related financing

                                        4


<PAGE>


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 the year ended  December 31, 1997,  $164.2
million for the year ended  December 31, 1998, and $43.1 million for the quarter
ended  March  31,  1999.  At March  31,  1999,  our  stockholders'  deficit  was
approximately  $(78.0)  million.  We and our  subsidiaries  will be permitted to
incur additional indebtedness in the future.

     Beginning  April  1,  2001,  AMSC  Acquisition  Company,  our  wholly-owned
subsidiary,  will be  allowed  to pay  dividends  to us to permit us to meet our
interest expenses with respect to our 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 as compared to less leveraged
          competitors.

We may need additional capital but it might not be available
- ------------------------------------------------------------

     We expect to continue  to make  significant  outlays to fund debt  service,
capital  expenditures and working capital,  both before and after we become cash
flow positive. While we believe that our cash resources,  together with existing
available  borrowings,  will be sufficient  to fund  operating  losses,  capital
expenditures,  working capital, and debt service through the time when we expect
to  generate  positive  free cash flow  sufficient  to fund these  items,  it is
possible that our cash flows from operations will be less than projected or will
not occur when  projected.  In such event,  we will require  additional  debt or
equity financing in amounts that could be material.  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.

     We cannot  guarantee  that our current  projections  will be accurate.  Our
projections  will depend upon numerous  future factors and  conditions,  many of

                                        5


<PAGE>




which are outside of our control. Our 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 introduce new products or services, our funding needs will increase,
possibly  to a  significant  degree.  If there is a rapid  increase  in customer
demand for recently announced products and services,  such as our eLink wireless
email service, we may need to order substantial  quantities of inventory,  which
will  require  significant  working  capital  which we may need to  finance.  In
addition, we are contractually  committed to purchase significant  quantities of
our  second  generation  two-way  messaging  device  and the  second  generation
terminal to be used with our  multi-mode  device.  If customer  demand for these
devices  does not  meet our  expectations,  we may need to  finance  significant
amounts of  inventory  purchases.  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  business  could  suffer if we cannot  keep pace with the  rapidly  changing
- --------------------------------------------------------------------
market for wireless communications
- ----------------------------------

     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.

     The market  for  wireless  communications  services  is also  marked by the
continuous  introduction of new products and services and increased capacity for
services  similar to those we  provide.  Future  technological  advances  in the
wireless  communications industry may result in the availability of new products
or  services.  Advances  may increase  the  efficiency  of existing  products or
services.  If a technology  becomes  available  that is more  cost-effective  or


                                       6


<PAGE>


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 the
financial and other resources available 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 to  establish  or
maintain a competitive position.

Our wireless business depends on market acceptance
- --------------------------------------------------

     The success of our wireless  communications business 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  depends on 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
some of our  services  and we cannot  guarantee  that any of them  will  achieve
market  acceptance  or generate  operating  cash flow.  If we cannot gain market
acceptance  for current or planned  products and services then our business will
be harmed.

     Based upon our expectations as to the 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  of future  equipment  purchases.  Accordingly,  any  material
miscalculation  with respect to our  operating  strategy or business  plan would
harm our business.

We may be unable to achieve our operating and financial objectives if we cannot
- -------------------------------------------------------------------------------
manage our growth effectively
- -----------------------------

     We may experience  periods of rapid expansion in our continuing  efforts to
respond to changing market conditions.  We will need to maintain and improve our
operating  and financial  systems and expand,  train and manage our employees in
order to  manage  growth  effectively  in the  complex  environment  in which we
operate. 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.

We may be unable to achieve our business and  financial  objectives  because the
- --------------------------------------------------------------------------
wireless communications 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,



                                        7


<PAGE>





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 and could  make it easier for new  competitors  to enter the
market. In addition,  increased competition has resulted in downward pressure on
pricing for certain of our products and services.

Our wireless business depends on proprietary information
- --------------------------------------------------------

         Our wireless  communications  business depends on technical  knowledge,
and we believe that our future success is based, in part, on our ability to keep
up with new technological  developments and incorporate them in our products and
services.  We own or  have  the  right  to use  certain  of our  work  products,
     inventions,  designs,  software,  systems  and  similar  know-how.  We must
diligently
protect  that  information,  and  while  we have  taken  steps to  protect  such
information,  we cannot  guarantee that the information will not be disclosed to
others  or that  others  will not  independently  develop  similar  information,
systems and  know-how.  We also rely on some  technologies  licensed  from third
parties.  We cannot be sure that these  licenses will remain  available to us on
commercially  reasonable  terms or at all. The loss of such  technologies  could
require us to obtain  substitute  technology  of lower  quality  or  performance
standards or at a greater cost, which could harm our business.

Our customers are highly  concentrated  and our business could suffer if we lost
- --------------------------------------------------------------------------------
key customers
- -------------

     After accounting for the acquisition of ARDIS in March 1998, five customers
(including  IBM)  accounted  for an aggregate of 40% of our service  revenue for
both the year ended  December 31, 1998, and the quarter ended March 31, 1999. In
addition, we recently signed an important strategic agreement with SkyTel, under
which SkyTel will market our eLink wireless email service to its customers.  The
loss of one or more of these customers or contracts, or any event, occurrence or
development  which adversely  affects our relationship with one or more of these
customers, or with
SkyTel, could harm our business.

Our business  could suffer if we do not meet the required  service  levels under
- --------------------------------------------------------------------------------
our contract with UPS and other large customer contracts
- --------------------------------------------------------

         Our  contract  with UPS  represents  the  largest  implementation  of a
wireless data service using our terrestrial  network,  calling for us to provide
wireless  service  for  approximately  50,000  UPS units by the end of 2001.  In
connection  with  this  contract,  we expect to incur  capital  expenditures  of
approximately  $7.1 million in 1999 and $5.2  million in 2000.  The UPS contract
includes  significant  warranties of performance.  If network availability drops
below 99%, we will be subject to an initial penalty of 2% of the average monthly
use of  service,  calculated  as the  average  of the last  three  months in the

                                        8


<PAGE>





affected area. The penalty increases if performance  levels drop further.  Also,
as part of the negotiations leading to the signing of the UPS contract, Motorola
issued a performance  guarantee to UPS regarding the network's  performance.  In
connection  with our  acquisition of ARDIS,  we agreed to indemnify  Motorola in
connection with such performance  guarantee.  We have deposited $10.0 million in
an escrow account that can be used to satisfy such indemnification  obligations.
In addition to the UPS contract,  most of our other  contracts,  including those
with large customers, contain warranties of performance and penalties associated
with failures of network performance.

The growth and  reputation  of our wireless  business  could suffer if our third
- --------------------------------------------------------------------------------
party vendors cannot provide adequate quantities of devices in a timely manner
- ------------------------------------------------------------------------------

     We  rely  on  independent  vendors  to  develop  and  manufacture  wireless
communications  devices for our networks,  which are significant elements of our
business plan because most of our services require such devices.  Certain of our
important  product  initiatives  are  dependent  on the timely  delivery  of new
generation devices, including the palm-sized device used with our eLink wireless
email service,  which is  manufactured by Research in Motion,  Limited,  and the
second  generation  terminal to be used with our  multi-mode  service,  which is
manufactured by Vistar  Telecommunications Inc. 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.  Vistar has delayed
its original timetable for delivery of the second generation terminal to be used
in our  multi-mode  device.  Currently,  delivery is  scheduled  to begin in the
second half of 1999. We cannot  guarantee  that we will not  experience  further
interruptions  or delays.  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 harmed.

     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.  We believe  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 revenues could be diminished.

     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


                                        9


<PAGE>






infrastructure  or become  unable to properly  maintain  our  existing  level of
operations. Such occurrences could harm our business.

Our  competitive  position  may be harmed if our  wireless  terrestrial  network
- --------------------------------------------------------------------------------
technology is licensed to others
- --------------------------------

     The terrestrial network, and certain of its competitive strengths,  such as
deep in-building penetration, is based upon a single frequency reuse technology.
Motorola holds the patent for this technology and, through our ARDIS subsidiary,
we hold a non-exclusive license to use this technology.  We also rely on support
agreements  with Motorola for support of the  operations of certain  portions of
the terrestrial  network.  However,  Motorola could enter into arrangements with
our competitors  and it is possible that such agreements  could harm our ability
to compete.

There are risks associated with satellite technology
- ----------------------------------------------------

     We  have  an  agreement  with  TMI  Communications  and  Company,   Limited
Partnership,  a  Canadian  mobile  satellite  owner and  operator,  for  backup,
restoral  and  additional  capacity  if our  MSAT-2  satellite  fails or we need
additional capacity. TMI owns and operates a satellite called MSAT-1. 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  malfunctions.  Recent MSAT-2  malfunctions have involved either components
backed  up by  spare  parts  or  did  not  have a  material  impact  on  current
operations.   However,   either  or  both  satellites  could  experience  future
malfunctions at any time,  which could damage our ability to serve our customers
and harm our reputation in the marketplace.

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

Our 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 terrestrial network has access to a remote  communications  backup
complex  that would  enable us to continue to provide  our  terrestrial  network
services  in the event of a natural  disaster  affecting  one  geographic  site.


                                       10


<PAGE>


However,  we do not currently  have access to a remote backup  satellite  ground
communications  facility  that would  enable us to  continue  to provide  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 wireless business is subject to domestic and international  regulation which
- --------------------------------------------------------------------------------
could impose significant costs or otherwise harm our business
- -------------------------------------------------------------

     The ownership  and  operations  of our wireless  communication  systems are
subject to  significant  regulation  by the FCC under  authority  granted by the
Communications  Act of 1934,  as amended,  and related  federal  laws. 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.
A number of our licenses are subject to renewal by the FCC.  Also, our satellite
operations  are  subject  to  international  frequency  coordination,  which may
require us to entertain  requests for  accommodation  by other nearby  satellite
systems.  We cannot  guarantee  that all existing  licenses  will be renewed and
requisite frequencies coordinated.  Current FCC regulations also generally limit
the ownership and control of our company by non-U.S.  citizens or entities to no
more than 25%, which could limit your  opportunity to receive a takeover premium
for your shares of common stock. In addition, despite our efforts to monitor our
foreign ownership,  there can be no assurance that non-U.S.  persons or entities
will not own in the aggregate  more than 25% of our common stock.  If this limit
is exceeded,  the FCC could potentially take a range of actions which could harm
our business.

     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
mobile  satellite  service in the United States.  We have opposed these filings.
However,  on July 20,  1998,  the FCC  granted  SatCom  Systems,  Inc. a Special
Temporary  Authority to operate up to 500 mobile  terminals in the United States
over  TMI's  satellite  for 180 days on a private  carrier  basis so that it may
conduct  marketing  trials;  this  Special  Temporary  Authority is likely to be
extended  until the FCC acts on  SatCom's  underlying  application.  On July 30,
1998, we filed an  Application  for Review and a Motion for Stay of this Special
Temporary  Authority  grant with the FCC, and these filings remain  pending.  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
restrain our ability to coordinate our spectrum access.

We could lose revenues or damage our reputation if we are not year 2000 ready
- -----------------------------------------------------------------------------

     Many currently  installed  computer systems and software products are coded
to accept only two-digit  entries in the date code field. Many such systems will
need to accept  four-digit  entries in order to  distinguish  20th century dates
from 21st  century  dates.  As a result,  before the end of this year,  computer
systems and software used by many  companies  need to be upgraded to comply with
these   "Year   2000"   requirements.   Otherwise   these   systems   may  cause
miscalculations  that will interfere with business  activities or simply fail to


                                       11





<PAGE>



work. When we use the terms "Year 2000 Ready" or "Year 2000  Readiness," we mean
that customers will not  experience any material  difference in performance  and
functionality  of our networks as a result of the date being prior to, during or
after the year 2000.

     We  expect  our  networks  to be Year  2000  Ready by the end of the  third
quarter of 1999. In addition, we are currently scheduled to complete renovation,
implementation  and rollout of our internal  systems,  including  our CMIS voice
customer billing  software,  in the fourth quarter of 1999. The cost of our Year
2000 Readiness program in 1998 was approximately $2.4 million,  and expenditures
for the Year  2000  Readiness  program  in 1999 are  estimated  to be up to $6.6
million, of which approximately $3.3 million was incurred as of June 30, 1999.

     The  estimated  cost and date to reach  Year  2000  Readiness  are our best
estimates.  There can be no  assurances  that we will achieve  these results and
actual results could differ materially from those anticipated.  Failure to solve
Year 2000 issues  within our critical  business  systems could result in service
outages,  miscalculations or disruption of operations that could have a material
adverse  impact on our business.  Also,  some of our critical  business  systems
depend  significantly  on software  programs,  products,  equipment and services
provided  to us by third  party  vendors  that are not  within  our  control.  A
significant Year 2000-related disruption of the services or equipment that third
party  vendors  provide  to us could  cause our  customers  to seek  alternative
providers or cause an unmanageable  burden on our customer service and technical
support,  which, in turn,  could harm our business.  We could also face customer
lawsuits for damages.

     Our Year 2000  Readiness  program may fail to foresee some risks or may not
address them  adequately.  Because of our  reliance on software,  some Year 2000
problems may not be found or the remediation efforts may introduce new bugs that
are not  identified  before they affect  operations.  If our  customers  fail to
become Year 2000 ready on time with their own  hardware  and  software  systems,
their  applications  may not  function  even if our systems are Year 2000 Ready.
This could result in reduced traffic and revenues.

     We strongly  urge you to read about our Year 2000 efforts under the heading
"Management's  Discussion  and  Analysis of Financial  Condition  and Results of
Operations -- Year 2000  Readiness"  contained in our annual report on Form 10-K
for the year ended December 31, 1998.

A small  number of  principal  stockholders  will own 85% of our stock and their
- --------------------------------------------------------------------------------
interests may conflict with yours as a stockholder
- --------------------------------------------------

     Our principal  stockholders are Hughes  Communications  Satellite Services,
Inc., Motorola, Inc., Baron Capital, Inc., Singapore Telecommunications Limited,
AT&T Wireless  Services,  Inc. and XM Ventures.  In addition,  we have agreed to
issue an additional 2,134,801 shares of our common stock to XM Ventures after we
obtain  approval  from our  stockholders.  After such shares are  issued,  these
stockholders will collectively hold in aggregate approximately 85% of our common
stock on a fully  diluted  basis.  We have entered into  material  contracts and
transactions with many of our principal stockholders and their affiliates and we

                                       12


<PAGE>



may enter into additional  contracts in the future.  These contracts include the
guarantee  of our debt  obligations.  Certain of these  stockholders  have other
interests in the  communications  industry that may conflict with our interests.
Certain of these  stockholders,  or their  affiliates,  have  contracts or other
relationships  with XM Radio, which has a different business plan than ours. For
example,  Hughes is  constructing  XM Radio's  satellites,  and  General  Motors
Corporation, which owns Hughes, has purchased $50.0 million of XM Radio's Series
A  subordinated  convertible  notes and entered  into a  long-term  distribution
agreement with XM Radio. DIRECTV  Enterprises,  Inc., a division of Hughes, also
has purchased  $50.0  million of XM Radio's  Series A  subordinated  convertible
notes and entered into an operational  assistance agreement with XM Radio. It is
possible  that these  stockholders'  interests in XM Radio could  conflict  with
their interests in American Mobile,  and, as a result,  these stockholders could
take  actions  that  might  not be in  our  interests  or  your  interests  as a
stockholder.  Also,  there can be no  assurance  that  these  stockholders  will
continue to retain their current ownership position in our company.

Our business would be harmed if we cannot attract and retain our key personnel
- ------------------------------------------------------------------------------

     We are  dependent on the efforts of a group of employees  with  specialized
technical and business knowledge  regarding our systems. If we lose the services
of one or more of these  individuals  it could harm our  business and our future
prospects.  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  our  business  would  suffer.  We do not  maintain  key man life
insurance on any of our officers or employees.

Our charter and bylaws contain  anti-takeover  provisions  that could  adversely
- --------------------------------------------------------------------------------
affect the price of our common stock
- ------------------------------------

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 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, which governs
business combinations with interested  stockholders and 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.



                                       13


<PAGE>



We do not intend to pay 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 price of our common stock is 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.


Future sales of our stock could adversely affect its price
- ----------------------------------------------------------

     Future sales of substantial  amounts of our common stock, or the perception
that such sales may occur,  could adversely affect the value of our common stock
and could impair our ability to raise  additional  capital in the future through
the sale of equity securities.  As of July 14, 1999, we had 39,136,801 shares of
common stock  outstanding.  Of these  shares,  approximately  12,000,000  shares
(including  5,322,600  shares  owned by Baron) are freely  tradable  in the open
market without  further  registration  under the  Securities Act of 1933.  Also,
12,615,662 shares  (including  2,070,884 shares that may be issued in the future
upon  exercise  of  outstanding  warrants)  are  registered  pursuant to a shelf
registration  statement  declared  effective  by  the  Securities  and  Exchange
Commission on March 31, 1999. In addition, we have provided certain registration
rights to other  stockholders  and owners of  warrants  to  purchase  our common
stock. These registration rights cover 6,666,622 shares of stock and warrants to
purchase an aggregate of 5,712,500 additional shares. In addition, we have filed
a registration statement covering the 8,614,244 shares issued or to be issued to
XM Ventures. Upon the effectiveness of such registration statement,  such shares
will be freely  tradable in the open market, subject to certain limitations,  as
described under the caption "Selling  Stockholders - Summary of Certain Material
Relationships with Selling Stockholders." We also have approximately 3.8 million
shares of common stock  reserved for issuance  under employee and director stock
option plans and other employee benefit plans, all of which shares, when issued,
are registered for resale.

XM Radio's business  involves  significant  risks and these risks may impair the
- --------------------------------------------------------------------------------
value of our investment in XM Radio
- -----------------------------------

     In addition to the risks  described above which relate to our core wireless
business and to our company  generally,  there are significant  risks associated

                                       14


<PAGE>




with our  investment  in XM  Radio.  These  risks  may  impair  the value of our
investment in XM Radio.  We describe these risks  separately in the section that
follows.

XM Radio is a development stage company and has not generated revenues to date
- ------------------------------------------------------------------------------

     XM Radio is a  development  stage  company  and still  needs to develop the
planned  XM  Radio  service  significantly  before  XM  Radio  can  offer  it to
consumers.  XM Radio  has not yet  generated  any  revenues.  XM Radio  will not
generate revenues from operations until the commencement of commercial operation
of its service.

XM Radio may never become profitable
- ------------------------------------

     Because XM Radio expects to incur  significant  expenses in the future,  it
will need to generate significant  revenues before it can become profitable.  XM
Radio's  ability to generate  revenues and ultimately to become  profitable will
depend upon several factors, including

     o    whether  it creates  and  implements  the XM Radio  system in a timely
          fashion;

     o    whether consumer  electronics  manufacturers  successfully develop and
          manufacture XM radios;

     o    whether  XM Radio  can  attract  and  retain  enough  subscribers  and
          advertisers to XM Radio;

     o    whether XM Radio can compete successfully; and

     o    whether   the  FCC   grants   XM  Radio   all   additional   necessary
          authorizations in a timely manner.


XM Radio has made significant  expenditures and incurred  significant  losses to
- --------------------------------------------------------------------------------
date and these are expected to grow
- -----------------------------------

     As of March 31, 1999, XM Radio had incurred costs of  approximately  $219.5
million in connection  with the  development  of the XM Radio  system.  XM Radio
incurred  aggregate net losses of approximately  $1.7 million from its inception
through  December  31, 1997,  and an  additional  $20.5  million in the 15-month
period ended March 31, 1999.  We expect XM Radio's net losses and negative  cash
flow to grow as XM Radio  builds its system,  makes  payments  under its various
contracts and begins to incur marketing costs.

XM Radio needs  substantial  further  financing but such financing  might not be
- --------------------------------------------------------------------------------
available
- ---------

     XM Radio needs substantial  additional financing to cover projected capital
expenditures and operating  expenses before it can generate any revenue from its
operations.  XM Radio estimates that it will need  approximately $750 million in
addition  to the amount it has raised  thus far in order to meet its needs until
it begins commercial  operation of its service,  which XM Radio is targeting for
the second  quarter of 2001.  On July 23, 1999, XM Radio  announced  that it had

                                       15


<PAGE>
filed a registration  statement with the Securities and Exchange  Commission for
an initial  public  offering of its common stock.  XM Radio expects that the net
proceeds  from such  offering  will be  sufficient  in the absence of additional
financing to cover XM Radio's funding needs into the first quarter of 2000. Even
after it  commences  commercial  service,  XM  Radio  will  require  significant
additional funds before it generates  positive cash flow. In addition,  XM Radio
has substantial payment obligations under a distribution  agreement with General
Motors, as described under the caption "XM Radio's  Distribution  Agreement with
General  Motors  involves  significant  financial  and other  risks." XM Radio's
actual funding requirements could vary materially from its projections, due to a
variety  of  factors,  some of which are  outside  of the  control  of XM Radio,
including  unexpected  costs,  unforeseen  delays,  engineering  design changes,
launch failures, satellite anomalies, adverse regulatory developments,  or other
unanticipated  events.  If one or more of these events occurs, XM Radio may have
to raise more funds than  expected  to remain in  business  and to  continue  to
develop and market the XM Radio system.

     We do not  intend to provide  any  material  portion of XM Radio's  funding
requirements.  XM Radio plans to raise  future  funds by selling  debt or equity
securities,  or both,  publicly and/or privately and by obtaining loans or other
credit  lines from banks or other  financial  institutions.  Any such  financing
would likely  decrease our economic and/or voting interest in XM Radio. XM Radio
may not be able to raise any such funds or obtain  any such  loans on  favorable
terms or at all. XM Radio's ability to obtain the required  financing depends on
several factors,  including future market conditions; XM Radio's success or lack
of success  in  developing,  implementing  and  marketing  its  satellite  radio
service;  XM Radio's  future  creditworthiness;  and  restrictions  contained in
agreements  with XM Radio's  investors or lenders.  If XM Radio is successful in
raising additional  financing,  it is anticipated that a significant  portion of
the  financing  will consist of debt  securities.  As a result,  XM Radio may be
highly leveraged.


     If XM Radio fails to obtain any necessary financing on a timely basis, then

     o    its satellite  construction,  launch, or other events necessary to its
          business could be materially  delayed, or their costs could materially
          increase;

     o    XM  Radio  could   default  on  its   commitments   to  its  satellite
          construction or launch  contractors,  creditors or others,  leading to
          termination  of   construction  or  inability  to  launch  XM  Radio's
          satellites; and

     o    XM Radio may not be able to launch  its  satellite  radio  service  as
          planned and may have to discontinue operations or seek a purchaser for
          its business or assets.

There are significant risks associated with satellite launches
- --------------------------------------------------------------

     Satellite  launches  have  significant  risks,  including  launch  failure,
satellite  destruction or damage during launch,  and improper orbital placement.
Launch  failure  rates vary  depending  on the  particular  launch  vehicle  and
contractor,  and there is virtually no track record for the specific rocket that
will be used for the launch of XM Radio's  satellites.  If one or more  launches


                                       16


<PAGE>



fail, XM Radio will suffer  significant  delay that will be very damaging to its
business,  and XM Radio will incur significant  additional costs associated with
the delay in revenue generating activities.

Satellites have limited lives and may fail during orbit
- -------------------------------------------------------

     XM Radio  cannot be certain of the  specific  longevity  of any  particular
satellite. Although its satellites are expected to have useful operational lives
of  approximately 15 years, a number of factors may decrease the useful lives of
XM Radio's satellites, including

     o    defects in construction;

     o    faster than expected degradation of solar panels;

     o    loss of fuel on board;

     o    random  failure of  satellite  components  that are not  protected  by
          back-up units;

     o    electrostatic storms; and

     o    collisions with other objects in space.

If a  satellite  were to fail  while in orbit,  XM Radio  would  either  have to
arrange for the launch of its ground  spare  satellite  or have to contract  for
additional  satellites to be built and launched.  Any such failure  likely could
affect the quality of XM Radio service,  substantially delay the commencement or
interrupt the continuation of XM Radio service and harm XM Radio's business.

XM Radio's system depends on development and integration of complex technologies
- --------------------------------------------------------------------------------
in a novel configuration that might not work
- --------------------------------------------

         XM  Radio's  service  will  transmit  signals  to XM  radios  using two
satellites,  supplemented by a terrestrial  repeater  network to relay satellite
signals.  This system will involve some new applications of existing  technology
and integration of two or more different and complex technologies, which may not
work as planned.  This system will also require  development of new technologies
and  finalization  of XM  Radio's  planned  system.  XM Radio may not be able to
successfully develop such technologies or its system.


     The use of  terrestrial  repeaters  with a  satellite  system  is  untested
- --------------------------------------------------------------------------------
and may not  provide  the  expected   transmission  quality.  XM  Radio's system
- -------------------------------------------------------
would use  satellites to broadcast  radio signals to portable  radios and radios
installed in cars and trucks,  which are highly mobile.  High  concentrations of
tall  buildings and other  obstructions  may block signals from the  satellites,
which would adversely affect satellite reception. XM Radio plans to address this
issue by installing a network of terrestrial  repeaters that will retransmit the



                                       17


<PAGE>

satellite  signal in areas  where  blockages  might  otherwise  occur.  Although
satellite and terrestrial repeater  transmission is existing  technology,  these
two systems have not been integrated and used together on the scale contemplated
by XM Radio. XM Radio cannot be certain that what it plans will work,  either in
terms of design or scale. In addition,  some areas with impediments to satellite
line of sight may still experience "dead zones."

     XM Radio's business plan relies on the timely development of XM radios.  XM
     ----------------------------------------------------------------------
Radio's  service  would be  received  by  specially  designed  receivers.  These
receivers,  which have not yet been developed, must be capable of receiving both
satellite  and  terrestrial  signals.  Although  these  radios  will be based on
existing   technologies,   they  will  require  a  unique  integration  of  such
technologies, which may take longer than expected.

     Integration  of  components of XM Radio's  system may  encounter  technical
     ---------------------------------------------------------------------------
difficulties.  XM  Radio  will  have to  integrate  a  number  of  sophisticated
- ------------
satellite  and other  wireless  technologies  before it can begin  offering  its
service.  Integration  of such a satellite  radio system is a complex task which
has not previously been accomplished. It will require XM Radio to integrate many
components which have not yet been fully developed and/or have not yet been used
as part of a combined system. Despite extensive testing of the components of the
XM Radio system, because of the nature and complexity of the XM Radio system, XM
Radio cannot  ultimately  confirm the ability of the system to function until XM
Radio has  actually  deployed  and tested a  substantial  portion of the system.
Hardware or software  errors in space or on the ground may limit or delay the XM
Radio service and therefore  reduce  anticipated  revenues.  There could also be
delays in the planned  development,  integration and operation of the components
of the XM Radio system. If the technological  integration of the XM Radio system
is not completed in a timely and effective  manner,  XM Radio's business will be
harmed.

XM Radio's planned launch of service may be delayed, which could harm XM Radio's
- --------------------------------------------------------------------------------
business and chances of success
- -------------------------------

     XM Radio plans to  commercially  launch its service in 2001. Its ability to
do so will  depend on several  important  factors.  Potential  causes of serious
delay include

     o    XM Radio's inability to obtain necessary financing in a timely manner;

     o    delays in, or modifications to, the design, development, construction,
          launch  or  testing  of  satellites,  terrestrial  repeaters  or other
          aspects of the XM Radio system;

     o    satellite launch failure;

     o    delays in manufacture or commercial availability of XM radios;

     o    obtaining additional authorizations from the FCC, if required; and

     o    coordinating spectrum use with Mexico.

Any  significant  delay in the  start of  commercial  operations  would  harm XM
Radio's  business  and decrease XM Radio's  chances of  competing  successfully.

                                       18


<PAGE>



During any period of delay,  XM Radio would  continue to have  significant  cash
requirements  that could materially  increase the aggregate amount of funding it
needs.  XM Radio may not be able to obtain  additional  financing  on  favorable
terms, or at all, during periods of delay.

XM Radio's  success  depends on the quality and performance of its satellite and
- --------------------------------------------------------------------------------
launch contractors
- ------------------

     Dependence upon satellite manufacturer to construct and deliver satellites.
     ---------------------------------------------------------------------------
XM Radio will rely on Hughes, its satellite  manufacturer,  to build and deliver
its  satellites  in a timely  manner.  If Hughes  fails to  deliver  functioning
satellites  in a timely  manner the  introduction  of XM Radio's  service  would
likely be  delayed.  If Hughes  were to deliver a  satellite  late or  otherwise
default,  the remedies XM Radio has will not adequately  compensate XM Radio for
any  damage  caused to its  business.  Although  XM Radio's  satellite  contract
provides for certain  remedies for late delivery,  Hughes will not be liable for
indirect or  consequential  damages,  or lost  revenues  or  profits,  from late
delivery or other defaults.  XM Radio's  satellite  contract  entitles Hughes to
certain excusable delays.

     Hughes has promised that the satellites will perform in accordance with the
specifications  and requirements of the satellite contract and will be free from
any  material  defect or failure or any  nonconformance  in design,  material or
workmanship.  However, XM Radio's only remedy if Hughes breaches this promise is
not to pay Hughes in-orbit  performance  incentive  payments of up to a total of
$12.5  million  for each  satellite.  This  remedy  likely  will not  adequately
compensate for the damage such breach would cause to XM Radio's business.

     Dependence  upon launch  services  provider.  XM Radio is  depending on Sea
     --------------------------------------------
Launch, the satellite launch services provider, to build its launch vehicles and
to launch the satellites.  If the satellite  launch  services  provider fails to
launch  the  satellites  in a timely  manner  XM Radio may be unable to meet its
business  plan  timetable.  Neither  Hughes nor the  satellite  launch  services
provider will be liable to XM Radio for any delay in delivery of the  satellites
up to 180 days caused by XM Radio's scheduled launch services provider.  A delay
of more than six  months  beyond the launch  period for either  satellite  would
allow XM  Radio,  subject  to  certain  conditions  (including  possibly  paying
additional fees to Hughes), to select an alternative launch system.  Although XM
Radio may be able to use another satellite launch services  provider,  switching
to another provider could involve  significant delay and a significant  increase
in cost.

XM Radio will depend on third party vendors to supply radios to customers
- -------------------------------------------------------------------------

         XM Radio's  strategy calls for  subscribers to buy XM radios from third
party  manufacturers  or their  distributors to receive XM Radio's  service.  XM
radios are not yet  available,  and XM Radio does not intend to  manufacture  or
distribute XM radios. XM Radio is negotiating with leading consumer  electronics
manufacturers  for the manufacture and distribution of XM radios for retail sale
in the United States. XM Radio has already signed contracts with Pioneer, Alpine
and Delphi-Delco  to  develop XM radios for use in the car, and a contract  with

                                       19


<PAGE>





SHARP to manufacture XM radios for use in the home.  However,  these  agreements
may not result in the timely production of enough affordable XM radios to permit
the widespread  introduction of XM Radio's service. If one or more manufacturers
fails to develop  these  products for timely  commercial  sale, at an affordable
price and with mass market nationwide distribution, XM Radio's revenues would be
less than expected and its business would suffer.

XM Radio  will be  subject  to  competition  from CD Radio and  traditional  and
- --------------------------------------------------------------------
emerging audio entertainment providers
- --------------------------------------

     In seeking market acceptance,  XM Radio will encounter competition for both
listeners and advertising revenues from many sources, including

     o    CD Radio, the other satellite radio licensee;

     o    traditional and, when available, digital AM/FM radio;

     o    Internet-based audio providers;

     o    direct broadcast satellite television audio service; and

     o    cable systems that carry audio service.

     CD Radio has  announced  that it expects to begin  receiving  revenue  from
commercial  operations in the first quarter of 2001,  and therefore may commence
operations   before  XM  Radio.  If  CD  Radio  begins   commercial   operations
significantly before XM Radio does, it may gain a competitive  advantage over XM
Radio.

     Unlike XM Radio,  traditional  AM/FM radio  already has a well  established
market for its services and generally offers "free" broadcast reception paid for
by commercial  advertising  rather than by a subscription  fee. Also, many radio
stations offer  information  programming of a local nature,  such as traffic and
weather reports, which XM Radio initially will be unable to offer as effectively
as local radio,  or at all. To the extent that  consumers  place a high value on
these  features of traditional  AM/ FM radio,  XM Radio will be at a competitive
disadvantage.

XM Radio's  distribution  agreement  with General  Motors  involves  significant
- --------------------------------------------------------------------------------
financial and other risks
- -------------------------

     XM Radio has  signed a  long-term  distribution  agreement  with the OnStar
division  of  General  Motors  providing  for the  installation  of XM radios in
General  Motors  vehicles  and the  distribution  of XM  Radio's  service to the
exclusion of other satellite  digital radio  services.  XM Radio has significant
annual,  fixed payment  obligations to General  Motors for four years  following
commencement of commercial  service.  These payments  approximate $35 million in
the aggregate during this period.  Additional  annual fixed payment  obligations
beyond  the  initial  four years of the  contract  term range from less than $35
million to approximately  $130 million through 2009,  aggregating  approximately
$400  million.  In order to  encourage  the broad  installation  of XM radios in
General Motors vehicles,  XM Radio has agreed to subsidize a portion of the cost


                                       20


<PAGE>



of XM radios,  and to make incentive  payments to General Motors when the owners
of General Motors  vehicles with installed XM radios become  subscribers for the
XM Radio  service.  XM Radio also must share with General Motors a percentage of
the subscription  revenue attributable to General Motors vehicles with installed
XM  radios,  which  percentage  increases  until  there  are more than 8 million
General Motors  vehicles with installed XM radios.  This agreement is subject to
renegotiation if GM does not achieve and maintain specified  installation levels
of General Motors  vehicles  capable of receiving XM Radio's  service,  starting
with 1.24 million  units after four years,  and the lesser of 600,000  units per
year  thereafter  and  amounts  proportionate  to  target  market  shares in the
satellite  digital  radio service  market.  There can be no assurances as to the
outcome  of any  such  renegotiation.  XM  Radio  may not be  able  to meet  its
obligations to General Motors under this agreement. In addition,  while XM Radio
and General  Motors have discussed  certain  installation  projections,  General
Motors is not required to meet any minimum  targets for  installing XM radios in
General Motors vehicles.  In addition,  certain of the payments to be made by XM
Radio  under this  agreement  will not be  directly  related to the number of XM
radios installed in General Motors vehicles.

XM Radio's  business  will depend on market  acceptance,  and the market for its
- --------------------------------------------------------------------------------
service is new and unproven
- ---------------------------

     There  is  currently  no  mobile  satellite  radio  service  in  commercial
operation in the United States.  As a result,  XM Radio cannot estimate with any
certainty  the  potential  demand  for such a service  or the degree to which XM
Radio will meet that demand. Furthermore,  there may not be sufficient demand to
enable XM Radio to earn  sufficient  revenues,  achieve  sufficient cash flow or
turn a profit.  Among other things,  consumer acceptance of XM Radio will depend
upon

     o    whether  XM  Radio   obtains,   produces   and  markets  high  quality
          programming consistent with consumers' tastes;

     o    the  willingness  of  consumers  to pay  subscription  fees to  obtain
          satellite radio service;

     o    the cost and availability of XM radios;

     o    XM Radio's  and its AM/FM  radio  competitors'  marketing  and pricing
          strategies;

     o    whether competitors develop new and alternative technologies providing
          audio entertainment; and

     o    general economic conditions.

Because  XM Radio  expects to derive a  significant  part of its  revenues  from
advertisers as well as  subscription  revenues,  advertiser  acceptance  will be
critical to the success of its business. XM Radio's ability to generate revenues
from advertisers will depend on several factors, including the level and type of
market  penetration of XM Radio's service,  competition for advertising  dollars
from other media, and changes in the advertising industry. Also, FCC regulations
may limit XM  Radio's  ability to offer its radio  service  to  non-subscribers.
These factors may reduce XM Radio's potential revenue from advertising.

                                       21


<PAGE>

CD Radio has filed a patent infringement suit against XM Radio
- --------------------------------------------------------------

     On January 12, 1999,  CD Radio,  the only other owner of an FCC license for
satellite  radio service,  commenced a lawsuit against XM Radio alleging that XM
Radio is infringing or will infringe three patents  assigned to CD Radio. The CD
Radio patents  involved in this  litigation  relate to certain aspects of signal
and reception methodologies that may be employed by a satellite radio system. In
its  complaint,  CD Radio  seeks  money  damages  to the  extent  XM  Radio  has
manufactured,  used or sold any product or method claimed in CD Radio's patents,
and an injunction.

     Based on the planned design of XM Radio's system,  XM Radio's  knowledge of
the  differences  between  the XM Radio  system  and the  claims of the CD Radio
patents and on advice XM Radio has received  from its patent  counsel,  XM Radio
believes that it has not  infringed and will not infringe any CD Radio  patents.
However,  the litigation could have a material adverse effect on XM Radio,  even
if XM Radio is successful.  It may divert management's attention and may make it
more  difficult for XM Radio to raise  financing or enter into other  agreements
with third parties,  and may impede XM Radio's  ability to move forward with the
development  of its system in a timely  manner.  If XM Radio does not prevail in
this litigation,  XM Radio could become liable to CD Radio for substantial money
damages  and/or be  subject  to an  injunction  preventing  XM Radio  from using
certain  technology in its satellite  radio system.  Any such  injunction  could
force XM Radio to  develop  new  technology  which  would not be  subject to the
injunction.  Alternatively,  XM Radio could be  required to license  alternative
technology  from a third party, or seek a license from, and pay royalties to, CD
Radio to use its  technology.  Any of the foregoing  could delay or increase the
costs of deploying XM Radio's system.

XM Radio's business may be impaired by third party intellectual property rights
- -------------------------------------------------------------------------------

     The  development  of  XM  Radio's  system  will  depend  largely  upon  the
intellectual property that XM Radio will develop and license from third parties.
If the intellectual  property that XM Radio may develop or use is not adequately
protected,  others will be permitted to duplicate the XM Radio system or service
without  liability.  There is no  guarantee  that others  will not develop  such
information,  technology  and  know-how.  In  addition,  others  may  challenge,
invalidate or circumvent XM Radio's  intellectual  property  rights,  patents or
existing sublicenses. Some of the know-how and technology XM Radio has developed
and plans to develop  will not be covered by U.S.  patents.  In order to protect
its  rights,  XM  Radio  will  seek to  rely  on  trade  secret  protection  and
contractual  agreements.  However,  those  agreements  may not provide  adequate
protection for XM Radio's trade secrets, know-how or other proprietary technical
information  if  there  is any  unauthorized  use or  disclosure.  The  loss  of
necessary technologies could require XM Radio to obtain substitute technology of
lower quality or performance  standards,  at greater cost or on a delayed basis,
which could harm XM Radio's business.


                                       22


<PAGE>




     Other parties may have patents or pending  patent  applications  which will
later mature into patents or  inventions  which may block XM Radio's  ability to
operate  its system or license  its  technology.  XM Radio may have to resort to
litigation  to enforce its rights under  license  agreements or to determine the
scope and validity of other parties' proprietary rights in the subject matter of
those licenses.  Such litigation could result in substantial cost, and there can
be no guarantee that XM Radio will succeed in any such litigation.

Oversight by the FCC and other regulatory bodies involves costs and risks
- -------------------------------------------------------------------------

     XM Radio license subject to continuing FCC oversight. As an owner of one of
     ----------------------------------------------------
two FCC licenses to operate a commercial  satellite  radio service in the United
States, XM Radio will continue to be subject to regulatory oversight by the FCC.
XM Radio's development, implementation and eventual operation of its system will
be subject to significant  regulation by the FCC under  authority  granted under
the  Communications   Act  of  1934,  as  amended,   and  related  federal  law.
Non-compliance by XM Radio with FCC rules and regulations could result in fines,
additional  license  conditions,  license  revocation or other  detrimental  FCC
actions.  Any of these FCC  actions  may harm XM Radio's  business.  There is no
guarantee that the rules and  regulations of the FCC will continue to support XM
Radio's business plan.

     License contains required milestones. The term of XM Radio's FCC license is
     ------------------------------------
eight years from the  commencement  of actual  commercial  operation  and may be
renewed.  The license  requires XM Radio to adhere to certain  milestones in the
development  of its  system,  including a  requirement  that XM Radio begin full
operation of its system by October 2003.  Because it depends on third parties in
certain  significant  respects,  XM  Radio  may not be  able to meet  all of the
milestones  contained  in its FCC  license.  If it fails to do so, the FCC could
take a range of actions, any of which may harm XM Radio's business.

     Challenge  to XM Radio's  license.  The award of XM Radio's FCC license was
     ---------------------------------
challenged by one of the losing bidders in the initial FCC licensing  procedure,
but the challenge  was denied by the FCC.  Subsequent to the award of XM Radio's
license,  the losing bidder filed with the FCC for reconsideration of XM Radio's
license  award.  Although XM Radio  believes  that the award of its license will
continue to be upheld, it cannot predict the ultimate outcome of this challenge.
If this challenge is successful,  the FCC could take a range of actions,  any of
which could harm XM Radio's ability to proceed with its planned  satellite radio
service.

     Interoperability requirement. The FCC's rules require interoperability with
     ----------------------------
all licensed satellite radio systems that are operational or under construction.
The FCC  conditioned XM Radio's license on  certification  that XM Radio's final
receiver  design is  interoperable  with the final receiver  design of the other
licensee, CD Radio, which plans to use a different transmission  technology than
XM Radio plans to use. Because of uncertainty regarding the design of CD Radio's
systems,  XM  Radio  may not be able  initially  to meet  this  interoperability
requirement.  XM  Radio  may  not  be  able  to  design  a  commercially  viable
interoperable  receiver,  and CD Radio  may not  cooperate  with XM Radio on the


                                       23


<PAGE>




issue of  interoperability.  Accordingly,  XM Radio  may not be able to meet the
FCC's interoperability  requirements and may need to obtain an extension of time
or  modification  of  this  requirement   from  the  FCC.   Complying  with  the
interoperability  requirement could make the radios more difficult and costly to
manufacture.   Accordingly,   this   requirement   could  delay  the  commercial
introduction of XM Radio's service.

     Further  approvals  needed for  repeater  system.  The FCC has  proposed to
     ------------------------------------------------
permit XM Radio to deploy  terrestrial  repeaters  to fill in gaps in  satellite
coverage.  However,  certain parties have opposed the FCC's proposal and the FCC
has not issued any final  orders  addressing  this  issue.  XM Radio's  plans to
deploy  such  terrestrial  repeaters  in its  system may be  impacted,  possibly
materially, by whatever rules the FCC issues in this regard.

     XM Radio  subject  to  coordination  risks.  XM Radio must  coordinate  its
     ------------------------------------------
domestic  uplink  station  networks  with other users of the  X-Band,  including
operators in the Fixed Services,  Broadcast Auxiliary  Services,  the Electronic
News Gathering Services and Mobile-Satellite Service uplink station networks. XM
Radio may not be able to coordinate  its use of this spectrum in a timely manner
or at all.  XM also will  need to  coordinate  the XM Radio  system  with  Fixed
Service  and  Mobile  Aeronautical  Telemetry  systems  operating  in  the  same
frequency bands in Canada and Mexico.  The U.S.  government,  which conducts the
coordination  process,  has  resolved  the  issue  with  Canada,  and has  begun
discussions with the Mexican government.  However,  the negotiations with Mexico
could be complicated by that country's  interest in developing a similar digital
satellite  radio service that might operate on the same  frequencies as XM Radio
will use in the United States.  Failure of the FCC to coordinate satellite radio
frequency use with Mexico could materially affect XM Radio's business.

     XM Radio subject to interference risks. XM Radio's system may be subject to
     --------------------------------------
interference  from licensees  operating in adjacent  frequency  bands.  Wireless
Communications  Service  licensees  operating in frequency bands adjacent to the
satellite  radio's  S-Band  allocation  must  comply  with  certain  out-of-band
emission limits imposed by the FCC to protect satellite radio systems.  In April
1998,  the FCC  proposed  to amend its  rules to allow  for new radio  frequency
lighting  devices that would operate in the  2400-2500  MHz  frequency  band. XM
Radio  opposed the  proposal on the grounds that the  proliferation  of this new
kind of lighting  and its proposed  emission  limits,  particularly  if used for
street  lighting,  may interfere with XM Radio.  Signal  quality,  and hence the
quality of XM Radio's service,  could be impaired if the FCC does not rule in XM
Radio's favor.

XM Radio could be vulnerable to risk of signal theft
- ----------------------------------------------------

     Like all  radio  transmissions,  the XM Radio  signal  will be  subject  to
interception.  "Pirates" may be able to obtain or  rebroadcast  XM Radio without
paying  the  subscription  fee.  Although  XM  Radio  plans  to  use  encryption
technology  to mitigate the risk of signal  theft,  such  technology  may not be
adequate to prevent theft of the XM Radio signal.  If  widespread,  signal theft
could harm XM Radio's business.

                                       24


<PAGE>






XM Radio needs to obtain rights to programming, which could be more costly than
- -------------------------------------------------------------------------------
anticipated
- -----------

     XM  Radio  must  negotiate  and  enter  into  music   programming   royalty
arrangements  with performing  rights  societies such as the American Society of
Composers, Authors and Publishers,  Broadcast Music, Inc., and SESAC, Inc. These
organizations  collect  royalties and distribute  them to songwriters  and music
publishers  and  negotiate  fees with  copyright  users based on a percentage of
revenues.  Radio  broadcasters  currently pay a combined total of  approximately
3-4% of their revenues to these performing rights societies. XM Radio expects to
negotiate  or  establish  by  arbitration   royalty   arrangements   with  these
organizations, but such royalty arrangements may be more costly than anticipated
or unavailable.

     Under the Digital Performance Right in Sound Recordings Act of 1995 and the
Digital Millennium Copyright Act of 1998, XM Radio also has to negotiate royalty
arrangements  with the owners of the sound  recordings.  The Recording  Industry
Association of America will negotiate  licenses and collect  royalties on behalf
of copyright owners for this performance right in sound recordings.  Cable audio
services currently pay a royalty rate of 6.5% of gross subscriber revenue.  This
rate was set by the  Librarian of  Congress,  which has  statutory  authority to
decide rates  through  arbitration,  and was  affirmed on May 21,  1999,  by the
United  States Court of Appeals for the District of Columbia.  Although XM Radio
believes it can distinguish itself sufficiently from the cable audio services in
order to negotiate a lower statutory rate, it may not be able to do so.

Insurance will provide limited protection to XM Radio
- -----------------------------------------------------

     XM Radio  intends  to  purchase  standard  launch  and  in-orbit  insurance
policies from global space insurance underwriters,  which would provide coverage
against total or partial loss of either  satellite during its expected life from
the time of launch.  Any  adverse  change in  insurance  market  conditions  may
substantially  increase  the  premiums  XM  Radio  would  have to pay  for  such
insurance.  If the launch of either  satellite  is a total or  partial  failure,
under certain  circumstances XM Radio's insurance may not fully cover XM Radio's
losses.  Further,  XM Radio does not expect to buy  insurance to cover  business
interruption,  loss of business or similar losses.  Also, any insurance XM Radio
obtains will likely contain  certain  customary  exclusions and material  change
conditions.

Rapid technological change could make XM Radio's service obsolete
- -----------------------------------------------------------------

     The  satellite  industry  and the  audio  entertainment  industry  are both
characterized by rapid technological  change,  frequent new product innovations,
changes  in  customer  requirements  and  expectations,  and  evolving  industry
standards.  Products using new  technologies,  or emerging  industry  standards,
could render XM Radio's technologies  obsolete.  In addition,  XM Radio may face
unforeseen  problems  when  developing  the XM Radio system which could harm its
business.

     Because XM Radio will depend on third parties to develop  technologies used
in key elements of the XM Radio system, more advanced  technologies which it may
wish to use may not be available to XM Radio on reasonable  terms or in a timely
manner.  Further,  XM Radio's  competitors may have access to  technologies  not
available to XM Radio, which may enable them to produce  entertainment  products
of greater interest to consumers, or at a more competitive cost.


                                       25


<PAGE>



                           AMERICAN MOBILE'S BUSINESS
                           --------------------------

General
- -------

     We are a nationwide  provider of wireless two-way data,  dispatch and voice
communications  services that enable  businesses  and mobile  workers to manage,
access, and transfer electronic information. We have developed a versatile array
of products and services  targeted at customers in four primary market segments:
(1) transportation and package delivery,  (2) field service,  (3) wireless email
and other Internet-based  content services,  and (4) telemetry,  which refers to
device to  device  communications  for  database  access  or remote  monitoring.
Customers  use our  products  and  services to connect  their  remote and mobile
equipment  and  people to their  enterprise  systems.  We deliver  our  services
through our own wireless network that uniquely integrates  separate  terrestrial
and satellite components.  Our customers typically sign multi-year contracts for
applications on our network such as:

       o  messaging  and call  dispatch  systems  used by  large  transportation
          companies and field service organizations,

       o  two-way wireless email services that provide mobile professionals with
          integrated  wireless access to a broad range of corporate and Internet
          email applications,

       o  telemetry and  point-of-sale  systems that connect  remote  equipment,
          such as utility  meters or wireless  point-of-sale  terminals,  with a
          central monitoring facility,

       o  global  position  tracking  systems that permit  businesses  to manage
          mobile assets, and

       o  point-to-multi-point  voice  communications  systems  used by  natural
          resource companies,  utilities, government agencies and other entities
          with mobile fleets and field workers.

     We offer customers the nation's largest,  most  fully-deployed  terrestrial
wireless two-way data network, comprising approximately 1,700 base stations that
provide  service to 427 of the  largest  cities and towns in the United  States,
including  virtually  all  metropolitan  areas.  We believe  that our  network's
extensive   nationwide  coverage  and  deep  in-building   penetration  are  key
competitive   advantages,   providing  customers  with  full  two-way  messaging
capability and guaranteed  message  delivery  through a single service  provider
with  nationwide  scope.  Our  satellite in  geosynchronous  orbit  overlays our
terrestrial network,  thereby extending the service area coverage of our network
throughout  all 50  states  and  the  Caribbean.  The  satellite  also  provides
nationwide voice and dispatch services.

     As of March 31, 1999 we had approximately  113,000 units on our network, of
which 99,600 were data units and 13,400 were voice  units.  On a pro forma basis
giving  effect to our  acquisition  of ARDIS  Company in March  1998,  our total
subscribers  grew by 30% during 1998 and 7% during the first quarter of 1999. In


                                       26


<PAGE>




addition,  we reduced  our EBITDA loss from  ($56.9)  million in 1997 to ($36.9)
million in 1998, on a pro forma basis for the ARDIS acquisition.

     Our principal  executive offices are located at 10802 Parkridge  Boulevard,
Reston, Virginia 20191-5416, and our telephone number is (703) 758-6000. We also
maintain an Internet site on the World Wide Web at www.ammobile.com. Information
contained at our web site is not, and should not be deemed to be, a part of this
prospectus.


Our Investment in XM Radio
- --------------------------

     In addition to our core  wireless  business,  we have an  investment  in XM
Satellite Radio Holdings Inc., a development stage company.  XM Radio is seeking
to become a  nationwide  provider of digital  quality  audio  entertainment  and
information  programming transmitted directly by satellites to vehicle, home and
portable  radios.  XM Radio owns one of two FCC  licenses to provide a satellite
digital audio radio service for the United  States.  XM Radio is developing  its
service,  which it will call "XM  Radio,"  to  provide a wide  variety of music,
news, talk, sports and other programming  offering up to 100 distinct  channels.
XM Radio  believes  that  customers  will be attracted to the broad  offering of
formats and the service's digital quality sound and coast-to-coast  coverage. XM
Radio is  constructing  its satellite  system and  contracting  with third party
programmers, vendors and other partners.

     On July 7, 1999, we acquired  WorldSpace,  Inc.'s debt and equity interests
in XM Radio,  other than a $75  million  loan from  WorldSpace  to XM Radio,  in
exchange for approximately 8.6 million shares of our common stock.  Concurrently
with this transaction,  XM Radio issued $250 million of subordinated convertible
notes to several new strategic and financial investors, including General Motors
Corporation,  Clear Channel Investments, Inc., DIRECTV Enterprises, Inc., Telcom
Ventures,  L.L.C., Columbia Capital and Madison Dearborn Partners. XM Radio used
$75  million  of the  proceeds  from such  notes to repay the  outstanding  loan
payable to WorldSpace.  As a result of these transactions,  WorldSpace no longer
owns any  direct  equity or debt  interest  in XM  Radio,  and we own all of the
issued and  outstanding  stock of XM Radio.  However,  on a fully  diluted basis
assuming a subsequent  conversion  of all  outstanding  convertible  notes of XM
Radio into XM Radio voting stock, we would own approximately 37% of the economic
interest in XM Radio.


Recent Developments - Results for the Quarter Ended June 30, 1999
- -----------------------------------------------------------------

     On July 26, 1999, we announced  certain financial and operating results for
the  second  quarter  ended  June 30,  1999.  Total  revenues  for the  quarter,
including  equipment sales,  increased to $22.9 million,  from $22.4 million for
the same period in 1998. Net service revenues for the quarter were $16.6 million
compared  with $16.7  million in the second  quarter  1998. We reported a second
quarter  EBITDA loss of ($10.5)  million and a net loss of ($42.4)  million,  or
($1.31) per share,  as  compared to an EBITDA loss of ($10.4)  million and a net


                                       27


<PAGE>




loss of ($43.0)  million,  or ($1.36)  per  share,  for the same  quarter of the
previous year.  Excluding  equity losses in XM Radio,  which we were required to
reflect  under  the  equity  basis of  accounting  as a result  of the  Exchange
Transaction  described  below,  the net loss for the second  quarter was ($39.2)
million,  or ($1.21) per share.  During the quarter,  we added 10,100 subscriber
units, ending at 123,100 as of June 30, 1999.

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

     We will not receive any proceeds  from the sale of the shares of our common
stock covered by this Prospectus.  The Selling  Stockholders will receive all of
the proceeds from any sales of our common stock covered by this prospectus.


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


Information About the Shares Owned by XM Ventures
- -------------------------------------------------

     We issued  6,479,443 shares of our common stock to XM Ventures in a private
transaction on July 7, 1999, and we have agreed to issue an additional 2,134,801
shares of our common  stock to XM Ventures  after we obtain the  approval of our
stockholders  to issue such shares.  A special meeting of our  stockholders  has
been  scheduled  for  September  7,  1999 to vote on a  proposal  to issue  such
additional shares.

     We  agreed  to issue  the  foregoing  shares  to XM  Ventures  as part of a
transaction  completed on July 7, 1999, in which we acquired WorldSpace,  Inc.'s
debt and  equity  interests  in XM Radio,  other  than a $75  million  loan from
WorldSpace to XM Radio, in exchange for  approximately 8.6 million shares of our
common  stock.  (In this  prospectus,  this  transaction  is  referred to as the
"Exchange  Transaction.")  For more information about the Exchange  Transaction,
please see the  discussion  under the  caption  "-  Summary of Certain  Material
Relationships with Selling Stockholders."

     Subject to certain  limitations,  XM Ventures  may sell the shares it owns.
Alternatively,  XM Ventures may  distribute any of the shares to the persons who
own shares of, or  options,  warrants  or other  rights to  purchase  shares of,
common stock of WorldSpace,  Inc. which is the beneficiary of XM Ventures,  who,
in turn, may sell such shares. If XM Ventures distributes shares it owns to such
persons, we will, if required, supplement this Prospectus to name any additional
selling stockholders.

     The following table shows, as of July 14, 1999, the number of shares of our
common  stock  that were  beneficially  owned by XM  Ventures  and the number of
shares that XM Ventures may offer under this  Prospectus.  We cannot provide you
with an estimate of the number of shares of common  stock that XM Ventures  will
hold in the future,  since XM Ventures may sell all,  some or none of its shares
of common stock. The following table (excluding the information  relating to the
percentage  of  shares   beneficially   owned)  has  been  prepared  based  upon
information provided to us by XM Ventures.


                                       28


<PAGE>




<TABLE>


                           Shares Owned Prior to Offering
                           ------------------------------
                                                                                             Shares Held
 <CAPTION>
                         Number of Shares(1)       Percent(2)        Shares Offered       After Offering
                           -------------------       ----------        --------------       --------------

<S>         <C>                  <C>                   <C>                <C>                     <C>
XM Ventures (3)                  8,614,244             20.87%             8,614,244               (4)
</TABLE>

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

(1)  Reflects  beneficial  ownership  of shares of common  stock prior to giving
     effect  to the  sale of the  shares  offered  by this  Prospectus.  Inclues
     2,134,801  shares that we have agreed to issue to XM  Ventures,  subject to
     stockholder  approval.  A  special  meeting  of our  stockholders  has been
     scheduled for September 7, 1999 to vote on a proposal to issue such shares.

(2)  Reflects  the  percentage  of  the  outstanding   shares  of  common  stock
     beneficially owned.

(3)  XM Ventures is a trust,  the  beneficiary of which is WorldSpace,  Inc. The
     trustee of XM Ventures is Noah A. Samara.  XM  Ventures'  address is 2400 N
     Street, N.W., Washington, DC 20037.

(4)  We cannot  provide  you with an  estimate of the number of shares of common
     stock that XM Ventures will hold in the future because XM Ventures may sell
     all, some or none of its shares of common stock.


Summary of Certain Material Relationships with Selling Stockholders
- -------------------------------------------------------------------

     Prior to July 7, 1999, WorldSpace owned 20% of the voting stock of XM Radio
and, between May 1997 and July 1999,  WorldSpace provided  approximately  $143.9
million of funding to XM Radio. The funds provided by WorldSpace constituted the
vast majority of XM Radio's funding prior to July 7, 1999.  WorldSpace's funding
to XM Radio took the form of both equity investments and loans,  including loans
represented  by notes  convertible  into XM Radio stock.  WorldSpace  also owned
certain options  exercisable for XM Radio stock.  Also, from May 1997 to July 7,
1999,  Noah Samara,  a  stockholder  of  WorldSpace,  served as a director of XM
Radio.  Prior to July 7, 1999, we and WorldSpace were parties to a shareholders'
agreement  addressing  certain board of director and other corporate  governance
matters relating to XM Radio.  This agreement was terminated upon the closing of
the Exchange Transaction.

     On July 7, 1999, we acquired  WorldSpace's  debt and equity interests in XM
Radio,  other than a $75 million loan from  WorldSpace to XM Radio,  in exchange
for approximately 8.6 million shares of our common stock.  Concurrently with the
Exchange Transaction,  XM Radio issued $250 million of subordinated  convertible
notes to several new strategic and financial investors,  and used $75 million of
the  proceeds  from  these  notes to  repay  the  outstanding  loan  payable  to
WorldSpace.  As a result of these  transactions,  we own all of the  issued  and
outstanding stock of XM Radio,  subject to the possibility of our interest being
reduced as described below.  WorldSpace no longer owns any direct equity or debt
interest in XM Radio.

                                       29


<PAGE>


     As  part  of the  Exchange  Transaction,  XM  Ventures  agreed  to  certain
restrictions  on the  transfer  of  shares  of our  common  stock  owned  by it.
Generally, XM Ventures initially may sell or distribute up to 1.7 million of its
shares,  and,  thereafter,  it may sell or distribute  an additional  20% of the
shares on or after each  three-month  anniversary  of July 7, 1999,  the date we
originally  issued shares to XM Ventures.  There are additional  restrictions on
the  transfer of such shares to ensure that we do not violate  applicable  legal
limits on the percentage of our stock that may be owned by non-U.S. citizens, as
well as certain other restrictions  contained in the Exchange Agreement executed
in connection with the Exchange Transaction.

     Also as part of the  Exchange  Transaction,  XM Ventures  agreed to certain
restrictions on its ability to vote its shares of our common stock. From July 8,
1999  until  the  first  date on  which XM  Ventures  and  certain  "significant
stockholders"  (as  defined  below)  hold less than 15% of the then  outstanding
shares of our common stock,  XM Ventures and each such  significant  stockholder
must,  with respect to any vote or consent by the holders of our common stock on
any matter,  be present in person or  represented by proxy at any meeting of our
stockholders  to  consider  such  matter,  and must vote their  shares of common
stock,  or sign any such consent,  in proportion to the votes or consents of all
other stockholders voting or consenting to such matter. Following the expiration
of this period,  XM Ventures and such  significant  stockholders  may vote their
shares of common stock as each determines in its own discretion. For purposes of
the foregoing  discussion,  "significant  stockholder" means each stockholder of
WorldSpace  or holder of options  or other  rights to  acquire  an  interest  in
WorldSpace as of June 7, 1999 that beneficially owns (within the meaning of Rule
13d-3 of the Securities  Exchange Act of 1934) more than one percent (1%) of the
then  outstanding  shares of our  common  stock,  provided  that in  calculating
beneficial ownership, no share may be counted more than once.


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

     When we issued the shares  covered by this  Prospectus  to XM  Ventures  as
described  above,  we  agreed to  register  such  shares  for  resale  under the
Securities Act of 1933.  This  agreement is contained in an Exchange  Agreement,
dated June 7, 1999,  by and among us, XM Radio and  WorldSpace.  This  agreement
requires us to file a "shelf" registration statement to register such shares. We
are also required to file such amendments and  supplements to such  registration
statement  and this  prospectus  with the SEC as may be necessary to comply with
applicable  securities law with respect to the  disposition of all of the shares
covered by the  registration  statement.  The Exchange  Agreement  also gives XM
Ventures  certain rights to include,  or "piggyback,"  shares of common stock in
other   registrations,   as  well  as  certain  rights  to  demand  underwritten
registrations.

     We may suspend the effectiveness of the "shelf" registration  statement, at
our option,  up to two times in any consecutive  365-day  period,  for no longer
than  reasonably  necessary and in no event longer than 30 consecutive  days per
suspension, separated, in each case, by at least 60 days from any prior blackout
period,  in the event of certain  significant  business  combinations or similar
material transactions, if (i) the Board of Directors determines, in the exercise
of its reasonable  judgment,  that  disclosure of such  transaction in the shelf
registration statement is not in our best interests,  and (ii) we provide notice
of such determination to XM Ventures.

                                       30


<PAGE>



     Whenever we propose to register any of our  securities  in an  underwritten
offering 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  covered  by this
registration statement, XM Ventures may request that we include, or "piggyback,"
in such  registration  all of the shares  issued to XM Ventures in the  Exchange
Transaction.  The  piggyback  registration  rights  granted to XM  Ventures  are
subject  and  subordinate  to the  registration  rights  under  all of our other
existing  registration  rights  agreements with other parties.  In addition,  XM
Ventures may not exercise their  piggyback  rights in connection  with our first
public offering that occurs after July 7, 1999.

     In  addition,  beginning  on the later of July 7, 2001 or the  exercise  or
expiration  of all demand  registration  rights under all of our other  existing
registration  rights  agreements with other parties,  but in no event later than
July 7, 2002,  irrespective of whether all demand  registration rights under all
of our other existing  registration  rights  agreements  with other parties have
been  exercised or expired,  XM Ventures  shall be entitled to two  underwritten
demand   registrations   on  customary  terms  and   procedures.   These  demand
registrations  are subject to the right of our Board of  Directors  to delay any
such registration for up to 90 days upon its good faith  determination that such
registration is not in our best interests at that time.


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

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

     o    underwritten public offerings;

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

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

     o    for the purpose of covering short positions; and

     o    in "block" sales.


                                       31


<PAGE>



     To the extent  required,  we will amend or supplement  this prospectus from
time to time to  describe  a  specific  plan  of  distribution.  If the  selling
stockholders  hire brokers or dealers to sell their shares of common stock,  the
selling  stockholders 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
under such Act may be sold under such  provisions  rather than  pursuant to this
prospectus.

     At the time any selling  stockholder makes a particular offer, if required,
we will  file,  and such  selling  stockholder  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 such selling  stockholder,  any discounts,  commissions or
other items  constituting  compensation  from such selling  stockholder  and any
discounts, concessions or commissions allowed or reallowed or paid to dealers.

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

     Our outstanding  common stock is listed on the Nasdaq National Market,  and
we have applied for listing of the  8,614,244  shares of common stock held by XM
Ventures on the Nasdaq National Market.

     We will bear the costs of  registering  the shares of our common stock held
by XM Ventures,  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 our counsel and all independent  certified  public  accountants
and underwriters (excluding discounts and commissions). XM Ventures, however, is
responsible  for the fees and  disbursements  of its separate  legal  counsel in
connection with the registration.


                                  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 S.  Segal,  our
Senior Vice  President,  General  Counsel and Secretary.  Ms. Segal owns 170,200
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 our
Stock  Option  Plan  which  options  are  vested  and  exercisable,  subject  to
compliance with applicable  securities  laws. Ms. Segal is also a Director of XM
Radio.

                                       32


<PAGE>


                                     EXPERTS
                                     -------

     The  consolidated   financial   statements  of  American  Mobile  Satellite
Corporation (the "Company") as of December 31, 1997 and 1998 and for each of the
years  in the  three-year  period  ended  December  31,  1998,  included  in the
Company's  Form 8-K dated July 9, 1999 and  incorporated  by  reference  in this
prospectus  and elsewhere in the  registration  statement,  have been audited by
Arthur  Andersen  LLP,  independent  public  accountants,  as indicated in their
report with  respect  thereto,  and are  included  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.
and  Subsidiary  (XM Radio) as of December 31, 1998 and 1997,  and for the years
ended December 31, 1998 and 1997 and for the period from December 15, 1992 (date
of inception) to December 31, 1998, have been  incorporated by reference  herein
and in the  registration  statement  in  reliance  upon the  report of KPMG LLP,
independent certified public accountants,  incorporated by reference herein, and
upon the  authority  of said firm as experts in  accounting  and  auditing.  The
report of KPMG contains an  explanatory  paragraph that states that XM Radio has
not commenced  operations,  has negative  working  capital and is dependent upon
additional debt and equity  financings,  which raise  substantial doubt about XM
Radio's  ability to  continue as a going  concern.  The  consolidated  financial
statements of XM Radio do not include any adjustments that might result from the
outcome of that uncertainty.


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

     We file annual,  quarterly and special reports,  proxy statements and other
information  with the SEC.  You may read and copy any  document we file with the
SEC at the SEC's public  reference rooms located at Room 1024, 450 Fifth Street,
N.W.,  Washington,  DC 20549, at 7 World Trade Center,  13th Floor, New York, NY
10048, and at Citicorp Center, 500 West Madison Street,  Suite 1400, Chicago, IL
60661.  You can also obtain  copies of filed  documents  by mail from the Public
Reference Section of the SEC at Room 1024, 450 Fifth Street, NW, Washington,  DC
20549.  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.

                    CERTAIN INFORMATION ABOUT THIS PROSPECTUS
                    -----------------------------------------

     We have filed a  registration  statement on Form S-3 with the SEC under the
Securities  Act of  1933  covering  the  common  stock  being  offered  by  this
prospectus. As permitted by SEC rules, this prospectus omits certain information
that is included in the registration statement. For further information about us
and our common  stock,  you should refer to the  registration  statement and its
exhibits.  Since the prospectus may not contain all the information that you may
find important,  you should review the full text of these documents.  If we have
filed a contract,  agreement or other document as an exhibit to the registration
statement,  you should read the exhibit for a more complete understanding of the
document  or matter  involved.  Each  statement  in this  prospectus,  including


                                       33


<PAGE>



statements  incorporated by reference as discussed below,  regarding a contract,
agreement  or other  document is  qualified  in its entirety by reference to the
actual document.

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

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

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

     c.   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;

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

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

     f.   our current  report on Form 8-K dated July 23, 1999 and filed with the
          SEC on July 26, 1999.

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

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




                                       34


<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.
<TABLE>

<S>                                                                     <C>
         SEC registration fee............. .....................        $ 45,000
         Legal fees and expenses................................          20,000
         Blue Sky fees and expenses.............................           2,500
         Accounting fees and expenses...........................          10,000
         Listing fees...........................................          17,500
         Miscellaneous..........................................           5,000
                                                                      ----------
      Total                                                             $100,000
</TABLE>



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 S. Segal, General Counsel, Senior  Vice President and
         Secretary.

23.1     Consent of Arthur Andersen LLP, independent public accountants.

23.2     Consent of KPMG LLP, independent certified public accountants.

23.3     Consent of Randy S. Segal,  General Counsel,  Senior 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).



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

(a)  The undersigned registrant hereby undertakes:

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

          (i)  To include any  prospectus  required  by section  10(a)(3) of the
               Securities Act of 1933;

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

                                      II-2


<PAGE>

         (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 th payment
     by the  registrant of expenses  incurred or paid by a director,  officer or
     controlling  person of the  registrant  in the  successful  defense  of any
     action,  suit or  proceeding)  is  asserted  by such  director,  officer or
     controlling person in connection with the securities being registered,  the
     registrant  will,  unless in the opinion of its counsel the matter has been
     settled  by  controlling  precedent,  submit  to  a  court  of  appropriate
     jurisdiction  the question  whether such  indemnification  by it is against
     public  policy as  expressed  in the Act and will be  governed by the final
     adjudication of such issue.



                                      II-3


<PAGE>





                                   SIGNATURES
                                   ----------

     Pursuant to the  requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-3 and has  duly  caused  this  registration
statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized in the County of Fairfax, Commonwealth of Virginia, on the 3rd day of
August, 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                August 3, 1999
- --------------------------    Executive Officer, and Director
Walter V. Purnell, Jr.        (Principal Executive Officer)


/s/ W. Bartlett Snell         Senior Vice President and          August 3, 1999
- ---------------------         Chief Financial Officer
W. Bartlett Snell             (Principal Financial and
                              Accounting Officer)




                                      II-4
<PAGE>





/s/ Gary M. Parsons           Chairman of the Board              August 3, 1999
- -------------------           of Directors
Gary M. Parsons

/s/ Douglas I. Brandon        Director                           August 3, 1999
- ----------------------
Douglas I. Brandon

/s/ Pradeep P. Kaul           Director                           August 3, 1999
- -------------------
Pradeep P. Kaul

/s/ Billy J. Parrott          Director                           August 3, 1999
- --------------------
Billy J. Parrott

/s/ Andrew A. Quartner        Director                           August 3, 1999
- ----------------------
Andrew A. Quartner

/s/ Jack A. Shaw              Director                           August 3, 1999
- ----------------
Jack A. Shaw

/s/ Roderick M. Sherwood, III Director                           August 3, 1999
- -----------------------------
Roderick M. Sherwood, III

/s/ Michael T. Smith          Director                           August 3, 1999
- --------------------
Michael T. Smith



                                      II-5


<PAGE>




                                                                       Exhibit 5



                                                                August 3, 1999



American Mobile Satellite Corporation
10802 Parkridge Boulevard
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 8,614,244 shares of Common Stock (the "Shares")
that may be sold by XM Ventures and certain other selling  stockholders named in
the Registration Statement (the "Selling  Stockholders"),  certain legal matters
in  connection  with the 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.

         As described  in the  Registration  Statement,  6,479,443 of the Shares
(the  "Issued  Shares")  were  issued to XM  Ventures  on July 7, 1999,  and the
remaining  2,134,801  Shares (the  "Additional  Shares")  are to be issued to XM
Ventures following approval of such issuance by the Company's stockholders.

         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:




<PAGE>









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

          2.   The Shares to be sold by the Selling  Stockholders have been duly
               authorized.

          3.   The Issued Shares have been validly issued and are fully paid and
               nonassessable.

          4.   The  Additional  Shares,   upon  issuance  and  delivery  thereof
               following   approval   of   such   issuance   by  the   Company's
               stockholders,   will  be   validly   issued,   fully   paid   and
               nonassessable.

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

         I hereby  consent  to the  filing of this  opinion  as Exhibit 5 to the
Registration Statement, and to the reference to my name under the caption "Legal
Matters" contained in the Registration Statement.


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










<PAGE>





                                                                    Exhibit 23.1



                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

As independent  public  accountants,  we hereby consent to the use of our report
dated March 29, 1999 (except with respect to the matter discussed in Note 18, as
to  which  the  date  is  July  7,  1999)  and to  all  references  to our  Firm
incorporated  by reference in or made a part of this  registration  statement on
Form S-3. Our report dated March 29, 1999 included in American Mobile  Satellite
Corporation's  Form  10-K for the year  ended  December  31,  1998 is no  longer
appropriate  since restated  financial  statements  have been  presented  giving
effect to a business combination.

/s/  ARTHUR ANDERSEN LLP
Washington, D.C.
August 2, 1999









                                                                    Exhibit 23.2


                          INDEPENDENT AUDITORS' CONSENT


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

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


                                                              /s/ KPMG LLP
McLean, VA

August 3, 1999









<PAGE>




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