CONFIDENTIAL

January 8, 2001

Motient Services Inc.
10802 Parkridge Blvd.
Reston, Virginia  20191-5416
Attn:  Gary M. Parsons

RE:      PROJECT UNION - RESTORAL CAPACITY AGREEMENT

Dear Gary:

This Restoral  Capacity Letter Agreement (the "RC Agreement") is entered into by
and between Motient Services Inc. ("MSI"),  a Delaware  corporation and a wholly
owned  subsidiary of Motient  Corporation  and TMI  Communications  and Company,
Limited  Partnership  ("TMI"),  a  Quebec  limited  partnership  and  indirectly
wholly-owned  by BCE Inc.  (each a "Party" and  collectively,  the "Parties") in
connection  with the  Investment  Agreement  by and among  Motient  Corporation,
Mobile  Satellite  Ventures LLC, the Existing  Investors,  the New Investors and
TMI, dated even date herewith (the "Investment Agreement").

1. The Transaction.  TMI and MSI shall provide  satellite  restoral  capacity to
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each other in accordance with the terms of this RC Agreement.

2. Definitions. In this RC Agreement:
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     "Affected  Party"  means  the Party  hereto  (TMI or MSI)  whose  satellite
     suffers a Satellite Degradation;

     "Degraded  Satellite"  means the satellite  hereunder (TMI Satellite or MSI
     Satellite)  that  suffers  a TMI  Satellite  Degradation  or MSI  Satellite
     Degradation, as the case may be;

     "Effective Date" means the date the Investment Agreement is entered into;

     "Joint Operating Agreement" means the joint operating agreement dated as of
     April 25, 1990 between AMSC Subsidiary  Corporation and Telesat Mobile Inc.
     (as assigned to TMI), as amended;

     "MSI Satellite" means the satellite owned by MSI as of the date hereof;

     "MSI  Satellite  Degradation"  means any  diminution or  degradation in the
     condition of the MSI Satellite  below that  specified in the monthly health
     report dated October 12, 2000.

     "Restoral  Capacity"  means use of the  Restoral  Satellite  in the form of
     Radio Frequency (RF) power;

     "Restoral  Satellite" means the satellite that provides  Restoral  Capacity
     with respect to a Satellite Degradation.

     "Satellite  Capacity  Agreement"  means the  memorandum  of  agreement  for
     satellite  capacity  dated as of February 17, 1992 between AMSC  Subsidiary
     Corporation and Telesat Mobile Inc. (as assigned to TMI) as amended;

     "Satellite  Degradation" means either a TMI Satellite  Degradation or a MSI
     Satellite Degradation.

     "Supporting  Party" means the Party hereto (TMI or MSI) whose  satellite is
     to provide Restoral Capacity to the Affected Party.

     "TMI Satellite" means the satellite owned by TMI as of the date hereof; and

     "TMI  Satellite  Degradation"  means any  diminution or  degradation in the
     condition  of the  TMI  Satellite  below  that  specified  in the  document
     entitled  "MSAT  Health  Report  to August  1,  2000",  a copy of which was
     provided to MSI through Motient Corporation under cover letter dated August
     10, 2000.

Capitalized  terms used herein and not otherwise  defined  herein shall have the
meanings ascribed thereto in the Investment Agreement.

3. Restoral Capacity.
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     (a) In  consideration  of the mutual  commitments  made hereunder,  and for
         other good and valuable  consideration  (the receipt and sufficiency of
         which is hereby  acknowledged),  each of MSI and TMI  agree to  provide
         each  other  Restoral  Capacity  pursuant  to  the  terms  of  this  RC
         Agreement,  and at no charge to the other Party for  Restoral  Capacity
         during the term of this Agreement. Any third party, out-of-pocket costs
         to provide the  Restoral  Capacity  will be the  responsibility  of the
         Affected Party.

     (b) In the event of any  Satellite  Degradation,  the  Affected  Party will
         attempt to reconfigure the Degraded  Satellite to the extent reasonably
         possible to mitigate the impact of such  Satellite  Degradation  and to
         minimize the amount of Restoral Capacity it may need to obtain from the
         Supporting Party.

     (c) If the  Affected  Party is  unable  to fully  mitigate  such  Satellite
         Degradation  as set out in  paragraph  3(b)  above,  then to the extent
         reasonably possible,  the Supporting Party shall,  immediately upon its
         receipt of a written  request for Restoral  Capacity  from the Affected
         Party,  commence to provide  Restoral  Capacity to the Affected  Party,
         provided  that for the purpose of this  paragraph  3(c),  the extent to
         which the other Party has Restoral Capacity available to provide to the
         Affected  Party will be determined  solely with reference to the amount
         of  capacity  the  Supporting   Party  is  actually   providing  and/or
         contractually  committed to provide and neither Party shall be required
         to provide  Restoral  Capacity to the Affected  Party if to do so would
         require the Supporting  Party to pre-empt any of its existing  customer
         commitments.

     (d) In  addition  to the  foregoing  limits,  in no  event  will a Party be
         required to provide Restoral Capacity that would result in the Affected
         Party having  access to more capacity than it had as of the date of the
         respective health report referred to above in paragraph 2.

     (e) The Parties will  cooperate  and use their  reasonable  best efforts to
         implement the use of Restoral  Capacity for the Affected  Party as soon
         as possible.

4. Termination of Restoral Obligations.
   -----------------------------------

     (i) This RC  Agreement,  and the Parties'  obligation  to provide  Restoral
         Capacity  hereunder,  shall be in effect from the Effective  Date,  and
         shall terminate on the sooner of (a) Closing or (b) when the Investment
         Agreement is terminated,  provided, however, that the provisions hereto
         shall  continue  in full force and effect for up to the earlier of: (i)
         an additional six months after such  termination and (ii) June 29, 2002
         in the event that either:  (x) the  Investment  Agreement is terminated
         solely  due  to  a  ruling  by  the  FCC  denying   approvals  for  the
         transactions,  or (y)  Motient  Corporation  (without  TMI's  approval)
         terminates  the Investment  Agreement,  pursuant to Section 11.2 of the
         Investment Agreement.

     (ii)The Satellite  Capacity Agreement is hereby suspended and the foregoing
         terms and conditions will govern the provision of restoral  capacity by
         each Party to the other,  until such time as the obligations to provide
         Restoral Capacity,  as set forth above, ceases. If this RC Agreement is
         terminated pursuant to this paragraph 4, and at such time the Satellite
         Capacity  Agreement has not been  terminated in accordance with its own
         terms,  then  effective  as of the  date  of  termination  of  this  RC
         Agreement:  (x) the  Satellite  Capacity  Agreement  shall  cease to be
         suspended  without any  further  action by the Parties and shall be and
         become operative and enforceable by the Parties  thereto;  and (y) upon
         TMI's request,  MSI will negotiate in good faith to amend the Satellite
         Capacity Agreement,  or enter into a new agreement, to sell capacity to
         TMI on commercial terms.

5. Binding Agreement.  This RC Agreement is intended by the Parties as a binding
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obligation of each of the Parties and their  respective  successors and assigns.
To  the  extent  that  any  provision  of  the  Joint  Operating   Agreement  is
inconsistent with any provision(s) of this RC Agreement,  the provisions of this
RC Agreement shall override the  inconsistent  provisions of the Joint Operating
Agreement.

6. Assignment. No Party hereto may assign this RC Agreement or any of its rights
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or  obligations  hereunder to any other person without the express prior written
approval of the other Party.

7.  Governing  Law.  This RC Agreement is being  executed and  delivered in, and
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shall be governed by and construed in accordance  with the laws of, the State of
New York,  without  regard to its principles of conflicts of law that would give
effect  to the  application  of the  law of  another  jurisdiction.  Each of the
Parties hereto hereby irrevocably and unconditionally  consents to submit to the
non-exclusive  jurisdiction  of the  courts  of the State of New York and of the
United States of America,  in each case having  jurisdiction  over the County of
New York, for any litigation arising out of or relating to this RC Agreement and
the transactions contemplated hereby and thereby (and agrees not to commence any
litigation  relating  thereto  except in such courts),  and further  agrees that
service of any process,  summons,  notice or document by U.S. registered mail to
its respective address set forth in this RC Agreement shall be effective service
of process for any litigation  brought against it in any such court. Each of the
parties hereto hereby  irrevocably and  unconditionally  waives any objection to
the laying of venue of any  litigation  arising out of this RC  Agreement or the
transactions  contemplated  hereby in the courts of the State of New York or the
United States of America,  in each case having  jurisdiction  over the County of
New York, and hereby further irrevocably and  unconditionally  waives and agrees
not to plead or claim in any such court that any such litigation  brought in any
such court has been brought in an inconvenient forum.

8. Severability. Whenever possible, each provision of this RC Agreement shall be
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interpreted in such manner as to be effective and valid, but if any provision of
this RC Agreement is held to be invalid or  unenforceable  in any respect,  such
invalidity or  unenforceability  shall not render invalid or  unenforceable  any
other provision of this RC Agreement.






9. Counterparts.  This RC Agreement may be executed simultaneously in one (1) or
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more counterparts,  each of which shall be deemed an original,  but all of which
together  shall  constitute  one and the same  agreement  binding on the Parties
hereto.

Please  indicate your  agreement to the terms set forth herein by executing this
RC Agreement below.

TMI Communications Inc., for and on behalf of
TMI Communications and Company, Limited Partnership


By:      /s/Larry Boisvert
         -----------------------------------------------------
Name:    Larry Boisvert
Title:   President and CEO

By:      /s/Ted Ignacy
         -----------------------------------------------------
Name:    Ted Ignacy
Title:   V.P. Finance

Accepted and agreed to as of this 8th day of January 2001:


Motient Services Inc.


By:  /s/Gary M. Parsons
     ------------------------------------------------
Name:    Gary M. Parsons
Title:   Chairman