EXHIBIT 10.18


                                VOTING AGREEMENT


         This VOTING AGREEMENT (this "Voting Agreement"), dated as of November
12, 2004, is entered into by and among those stockholders of Mobile Satellite
Ventures GP Inc., a Delaware corporation ("General Partner") and General
Partner of Mobile Satellite Ventures LP, a Delaware limited partnership ("MSV
LP"), listed on Schedule I hereto (each individually, a "Stockholder," and
collectively, the "Stockholders")).

                                    RECITALS

         WHEREAS, each Stockholder owns shares of common stock, par value $0.01
per share, of General Partner (the "Shares"), as well as units of limited
partnership interest of MSV LP;

         WHEREAS, MSV LP and General Partner have entered into purchase
agreements (the "Purchase Agreements") with Motient Ventures Holding
Inc.("Motient") and certain other purchasers (collectively, the "Purchasers"),
pursuant to which the Purchasers will make an equity investment in MSV LP and
General Partner (the "Equity Investments");

         WHEREAS, in connection with the Equity Investments, General Partner,
the Stockholders, and Motient are entering into that certain Amended and
Restated Stockholders' Agreement, dated as of November 12, 2004 (the "GP
Stockholders' Agreement");

         WHEREAS, in connection with the Equity Investments and the concurrent
execution of the GP Stockholders' Agreement, the Stockholders wish to enter
into this Voting Agreement to memorialize their understandings and agreements
regarding the manner in which the Stockholders will vote with respect to
certain matters.

         NOW, THEREFORE, in consideration of the agreements contained herein
and for other good and valuable consideration, the receipt and sufficiency of
which is hereby acknowledged, the parties to this Voting Agreement hereby agree
as follows:

ARTICLE I     Defined Terms
              -------------

         Section 1.01. Definitions. The terms defined in this Article I shall,
for the purposes of this Voting Agreement, have the meanings herein specified.
In addition, any capitalized terms used in this Voting Agreement but not
defined herein shall have the meanings given such term in the GP Stockholders'
Agreement.

         "Affiliate" means any person or entity that directly or indirectly
controls, is controlled by, or is under common control with, the specified
person or entity. As used in this definition, the term "control" means the
possession, directly or indirectly, of the power to direct or cause the
direction of the management and policies of an entity, whether through
ownership of voting securities, by contract or otherwise.

         "Board" means General Partner's Board of Directors.

         "Columbia Group" means the entities listed under the caption "Columbia
Group" in Schedule I, as well as any subsequent owner of Shares or Units owned
by the Columbia Group as of the date of this Agreement, where such Shares or
Units are transferred to such subsequent owner in accordance with the terms of
Section 2.03 of this Agreement.

         "Equity Investments" has the meaning given to such term in the
Recitals.

         "General Partner" has the meaning given to such term in the Preamble.

         "GP Stockholders' Agreement" has the meaning given to such term in the
Recitals.

         "Investor Group" means each of the following: (i) the TMI Group; (ii)
the MSV Investors Group; (iii) the Telcom/Columbia/Spectrum Group, and (iv) the
Motient Group.

         "Major Transaction" means (a) the merger or consolidation of MSV LP or
General Partner into or with another corporation in which the limited partners
of MSV LP or the stockholders of General Partner, as applicable, and the
Affiliates of such limited partners or stockholders immediately preceding such
merger or consolidation (solely by virtue of their units, shares or other
equity interests of MSV LP or General Partner, as applicable) shall own less
than 51% of the outstanding voting securities of the surviving corporation; (b)
the sale, transfer or lease (but not including a transfer or lease by pledge or
mortgage to a bona fide lender for so long as such lender has no right to
accelerate the maturity of the indebtedness to which such pledge or mortgage
relates), whether in a single transaction or pursuant to a series of related
transactions or plan, of all or substantially all the assets of MSV LP or
General Partner, which assets shall include for these purposes 50% or more of
the outstanding voting capital stock of any subsidiaries of MSV LP or General
Partner, as applicable, the assets of which constitute all or substantially all
the assets of MSV LP or General Partner and its subsidiaries taken as a whole;
(c) the sale, transfer or lease (but not including a transfer or lease by
pledge or mortgage to a bona fide lender for so long as such lender has no
right to accelerate the maturity of the indebtedness to which such pledge or
mortgage relates), whether in a single transaction or pursuant to a series of
related transactions, of all or substantially all the assets of subsidiaries of
MSV LP or General Partner, the assets of which constitute all or substantially
all of the assets of MSV LP or General Partner, as applicable, and its
subsidiaries taken as a whole; or (d) the liquidation, dissolution or winding
up MSV LP or General Partner or of such of MSV LP's or General Partner's
subsidiaries, as applicable, the assets of which constitute all or
substantially all of the assets of the business of MSV LP or General Partner,
as applicable, and its subsidiaries taken as a whole, whether voluntarily or
involuntarily.

         "Motient" has the meaning given to such term in the Recitals.

         "Motient Group" means Motient and any other Affiliate of Motient that
owns Shares or Units, as well as any subsequent owner of Shares or Units owned
by the Motient Group as of the date of this Agreement.

         "MSV Investors Group" means the entities listed under the caption "MSV
Investors Group" in Schedule I, as well as any subsequent owner of Shares or
Units owned by the MSV Investors Group as of the date of this Agreement, where
such Shares or Units are transferred to such subsequent owner in accordance
with the terms of Section 2.03 of this Agreement.

         "MSV LP" has the meaning given to such term in the Preamble.

         "Parent Transfer/Drag Along Agreement" means that certain Amended and
Restated Parent Transfer/Drag Along Agreement, dated as of August 21, 2003, by
and among MSV LP, General Partner, Motient Corporation, Motient Ventures
Holding Inc., TMI Communications and Company, Limited Partnership, TMI
Communications Delaware, Limited Partnership, and the Investor Parents (as
defined therein), as amended.

         "Partnership Agreement" means that certain Amended and Restated
Limited Partnership Agreement of MSV LP, dated as of November 12, 2004, as
amended from time to time, by and among General Partner and the limited
partners named therein.

         "Purchase Agreements" has the meaning given to such term in the
Recitals.

         Purchasers" has the meaning given to such term in the Recitals.

         "Shares" has the meaning given to such term in the Recitals.

         "Spectrum Group" means the entities listed under the caption "Spectrum
Group" in Schedule I, as well as any subsequent owner of Shares or Units owned
by the Spectrum Group as of the date of this Agreement, where such Shares or
Units are transferred to such subsequent owner in accordance with the terms of
Section 2.03 of this Agreement.

         "Telcom Group" means the entities listed under the caption "Telcom
Group" in Schedule I, as well as any subsequent owner of Shares or Units owned
by the Telcom Group as of the date of this Agreement, where such Shares or
Units are transferred to such subsequent owner in accordance with the terms of
Section 2.03 of this Agreement.

         "Telcom/Columbia/Spectrum Group" means, collectively, the Telcom
Group, the Columbia Group, and the Spectrum Group.

         "TMI Group" means the entities listed under the caption "TMI Group" in
SCHEDULE I, as well as any subsequent owner of Shares or Units owned by the TMI
Group as of the date of this Agreement, where such Shares or Units are
transferred to such subsequent owner in accordance with the terms of Section
2.03 of this Agreement.

         "Unit" means a unit of limited partnership interest in MSV LP with the
rights and privileges specified in the Partnership Agreement.

ARTICLE II    Voting Agreements
              -----------------

         Section 2.01. Voting of Shares and Units. To the extent the
Stockholders are entitled or required to vote their Shares or Units with
respect to any of the following actions (whether pursuant to law or agreement
or otherwise), none of the Stockholders shall vote its Shares or Units, or
execute a written consent with respect to such Shares or Units, in favor of any
of the following actions, unless at least three of the four Investor Groups are
in favor of such action:

         (a) Major Transactions. The consummation by General Partner or MSV LP,
directly or indirectly, of any Major Transaction, or the entry by MSV LP or
General Partner into a binding agreement with respect to a Major Transaction;

         (b) Material Changes to Organizational Documents. The amendment,
alteration, waiver or termination of any provision of (i) the certificate of
incorporation of General Partner, (ii) the bylaws of General Partner, (iii) the
Certificate of Limited Partnership of MSV LP, (iv) the Partnership Agreement,
(v) the GP Stockholders' Agreement, or (v) the Parent Transfer/Drag Along
Agreement, in each case in any manner that materially affects the rights,
privileges or obligations of the stockholders of General Partner or the limited
partners of MSV LP;

         (c) Acquisition of More than 49% of Shares or Units. The acquisition,
in any transaction or series of related transactions, by any stockholder of
General Partner or limited partner of MSV LP (including any Affiliates of such
stockholders or limited partners) of direct or indirect ownership of more than
49% of (i) the outstanding Shares or (ii) the outstanding Units (including in
each case any Shares or Units attributable to unexercised options or warrants
or other similar securities owned by such stockholder or limited partner or
their Affiliates); or

         (d) Exercise of Drag Along Rights. Any exercise of the "drag along"
rights set forth in Section 8.5(b) of the GP Stockholders' Agreement,
including, for the avoidance of doubt, any delivery of a Drag-Along Notice (as
defined in Section 8.5(b) of the GP Stockholders' Agreement).

         Section 2.02. Board Votes. For so long as any Stockholder or Investor
Group is entitled to designate one or more directors on the Board, each
Stockholder agrees to cause its (or its Investor Group's) designees on the
Board to cast their votes as directors with respect to any of the matters
described in Section 2.01 above in a manner consistent with the agreements set
forth in Section 2.01 above; provided, that nothing in this Voting Agreement
shall be deemed to require a director to take any action, or refrain from
acting, in a manner inconsistent with such director's fiduciary duties under
Delaware law.

         Section 2.03. Purchasers and Transferees Bound. In addition to any
other requirements of the Partnership Agreement or the GP Stockholders'
Agreement relating to a transfer of Units or Shares, no Units or Shares shall
be sold, assigned, transferred or otherwise disposed of by any of the
Stockholders unless the purchaser or transferee of such Units or Shares
executes a written agreement or instrument accepting, with respect to the Units
or Shares acquired by such purchaser or transferee, all of the terms and
conditions set forth in this Voting Agreement and agreeing to be bound thereby.
Following any such transfer of Shares or Units, such Shares or Units shall
remain subject to the provisions of this Voting Agreement, and the purchaser or
transferee of such Shares or Units shall be deemed, for all purposes of this
Voting Agreement, to be a member of the same Investor Group as the Stockholder
from which such Shares or Units were acquired.

         Section 2.04. Rules of Construction.

         (a) Telcom/Columbia/Spectrum Group. Concurrent with the execution of
this Voting Agreement, the Telcom/Columbia/Spectrum Group shall deliver a
written instrument, signed by each Stockholder that is a member of such Group,
to the other Stockholders, stating the method by which the
Telcom/Columbia/Spectrum Group will express its binding vote to the other
Stockholders for matters to be voted on pursuant to this Voting Agreement. Such
methodology shall be selected by the members of the Telcom/Columbia/Spectrum
Group in their discretion, but the methodology indicated in such written
instrument shall be binding on such Stockholders unless and until a subsequent
written instrument is delivered, signed by each Stockholder that is a member of
the Telcom/Columbia/Spectrum Group, changing such methodology.

         (b) Shares and Units Transferred to Other Parties. For the avoidance
of doubt, in the case of any votes or consents required by this Voting
Agreement, Shares or Units that are sold or transferred by Stockholders who are
members of one of the Investor Groups shall continue to be counted as Shares or
Units, as the case may be, owned by members of such selling Stockholder's
Investor Group. In addition, after the date of this Agreement, if any
Stockholders sell or transfer less than all of the Shares or Units owned by
such Stockholder's Investor Group to one or more persons not already members of
such Stockholder's Investor Group, then, no later than the effective date of
such sale or transfer, the Stockholder shall deliver a written instrument
signed by both the transferor and transferee(s) to each other Stockholder,
stating the method by which such transferring Stockholder's Investor Group will
express its binding vote to the other Stockholders for matters to be voted on
pursuant to this Voting Agreement.

ARTICLE III   Miscellaneous
              -------------

         Section 3.01. Term. This Voting Agreement, and the obligations of the
parties hereunder, shall survive and remain in effect until November 12, 2007,
or such other date as shall be agreed by two of the three Investor Groups party
to this Agreement (including, for this purpose, any of such Investor Group's
permitted transferees or assignees).

         Section 3.02. Amendments. This Voting Agreement may be amended or
modified, and the rights and obligations of the parties to this Agreement may
be waived, only upon the written consent of two of the three Investor Groups
party to this Agreement (including, for this purpose, any of such Investor
Group's permitted transferees or assignees).

         Section 3.03. Governing Law. This Agreement shall be governed in all
respects by the law of the State of New York as such law is applied to
agreements between New York residents entered into and performed entirely in
the State of New York, without regard to the conflict of laws provisions
thereof.

         Section 3.04. Successors and Assigns. Without in any way limiting the
applicability of other provisions of this Agreement that may be applicable, the
provisions hereof shall inure to the benefit of, and be binding upon, the
successors, assigns, heirs, executors and administrators of the parties hereto.
Nothing in this Agreement, express or implied, is intended to confer upon any
other party (other than the parties to this Agreement or their respective
successors and assigns) any rights, remedies, obligations or liabilities under
or by reason of this Agreement, except as expressly provided in this Agreement.

         Section 3.05. Severability. In case any provision of this Agreement
shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby; provided, that no such severability shall be effective if it
materially and adversely affects the economic benefit of this Agreement to any
party.

         Section 3.06. Notices. All notices required or permitted hereunder
shall be in writing and shall be deemed effectively given (a) upon personal
delivery to the party to be notified, (b) when sent by confirmed facsimile if
sent during normal business hours of the recipient, if not, then on the next
business day, (c) five days after having been sent by registered or certified
mail, return receipt requested, postage prepaid, or (d) one day after deposit
with a nationally recognized overnight courier, specifying next day delivery,
with written verification of receipt. All communications shall be sent to each
Stockholder at the address designated by such party in Schedule I.

         Section 3.07. Equitable Relief. Each Stockholder agrees that if it
fails to perform its obligations under this Agreement for any reason
whatsoever, the other parties hereto shall be entitled to specific performance
and injunctive or other equitable relief, and each Stockholder hereby further
agrees to waive any requirement for the securing or posting of any bond in
connection with the obtaining of any injunctive or other equitable relief. This
provision is without prejudice to any other rights that the other parties to
this Agreement may have against any other party for any failure to perform its
obligations under this Agreement.

         Section 3.08. Further Assurances. Each Stockholder shall at any time
and from time to time promptly execute and deliver to the other Stockholders
such further instruments, consents and other documents and take such further
action as such other Stockholders may reasonably require in order to carry out
the full intent and purpose of this Agreement.

         Section 3.09. Interpretation. The titles of the sections and
subsections of this Agreement are for convenience of reference only and are not
to be considered in construing this Agreement. All pronouns contained herein,
and any variations thereof, shall be deemed to refer to the masculine, feminine
or neutral, singular or plural, as to the identity of the parties hereto may
require.

         Section 3.10. Counterparts. This Agreement may be executed in any
number of counterparts, each of which shall be an original, but all of which
together shall constitute one instrument. Delivery of an executed counterpart
of a signature page of this Agreement by facsimile shall be effective as
delivery of a manually executed counterpart of this Agreement.

         Section 3.11. Entire Agreement. This Agreement, the Schedules hereto
and any other documents delivered pursuant hereto constitute the full and
entire understanding and agreement between the parties with regard to the
subjects hereof and supersede any and all prior and contemporaneous agreements
or understandings, whether expressed or implied, written or oral, between the
parties with respect hereto and thereto. No party shall be liable or bound to
any other in any manner by any representations, warranties, covenants and
agreements except as specifically set forth herein and therein.


                            [Signature Pages Follow]



         IN WITNESS WHEREOF, the parties hereto have duly executed this Voting
Agreement as of the date first above written.

                                    MSV INVESTORS, LLC

                                    By:  /s/ Jeffrey A. Leddy
                                         --------------------------------
                                         Name:  Jeffrey A. Leddy
                                         Title: CEO


                                    TMI COMMUNICATIONS DELAWARE,
                                         LIMITED PARTNERSHIP

                                    By:  3924505 Canada, Inc., its General
                                         Partner

                                    By:  /s/ Rory McCormick
                                         --------------------------------
                                         Name:  Rory McCormick
                                         Title: President


                                    TELCOM SATELLITE VENTURES II, INC.

                                    By:  /s/ Hal B. Perkins
                                         --------------------------------
                                         Name:  Hal B. Perkins
                                         Title: VP and General Counsel


                                    TELCOM SATELLITE VENTURES, INC.

                                    By:  /s/ Hal B. Perkins
                                         --------------------------------
                                         Name:  Hal B. Perkins
                                         Title: VP and General Counsel


                                    SPECTRUM SPACE EQUITY INVESTORS IV-II, INC.

                                    By:  /s/ Kevin J. Maroni
                                         --------------------------------
                                         Name:  Kevin J. Maroni
                                         Title: Authorized Signatory


                                    SPECTRUM SPACE IV PARALLEL II, INC.

                                    By:  /s/ Kevin J. Maroni
                                         --------------------------------
                                         Name:  Kevin J. Maroni
                                         Title: Authorized Signatory


                                    SPECTRUM SPACE IV MANAGERS II, INC.

                                    By:  /s/ Kevin J. Maroni
                                         --------------------------------
                                         Name:  Kevin J. Maroni
                                         Title: Authorized Signatory


                                    SPECTRUM SPACE EQUITY INVESTORS IV, INC.

                                    By:  /s/ Kevin J. Maroni
                                         --------------------------------
                                         Name:  Kevin J. Maroni
                                         Title: Authorized Signatory


                                    SPECTRUM SPACE IV PARALLEL, INC.

                                    By:  /s/ Kevin J. Maroni
                                         --------------------------------
                                         Name:  Kevin J. Maroni
                                         Title: Authorized Signatory


                                    SPECTRUM SPACE IV MANAGERS, INC.

                                    By:  /s/ Kevin J. Maroni
                                         --------------------------------
                                         Name:  Kevin J. Maroni
                                         Title: Authorized Signatory


                                    COLUMBIA SPACE (QP) II, INC.

                                    By:  /s/ Donald A. Doering
                                         --------------------------------
                                         Name:  Donald A. Doering
                                         Title: Authorized Signatory


                                    COLUMBIA SPACE (AI) II, INC.

                                    By:  /s/ Donald A. Doering
                                         --------------------------------
                                         Name:  Donald A. Doering
                                         Title: Authorized Signatory


                                    COLUMBIA SPACE PARTNERS II, INC.

                                    By:  /s/ Donald A. Doering
                                         --------------------------------
                                         Name:  Donald A. Doering
                                         Title: Authorized Signatory


                                    COLUMBIA SPACE (QP), INC.

                                    By:  /s/ Donald A. Doering
                                         --------------------------------
                                         Name:  Donald A. Doering
                                         Title: Authorized Signatory


                                    COLUMBIA SPACE (AI), INC.

                                    By:  /s/ Donald A. Doering
                                         --------------------------------
                                         Name:  Donald A. Doering
                                         Title: Authorized Signatory


                                    COLUMBIA SPACE PARTNERS, INC.

                                    By:  /s/ Donald A. Doering
                                         --------------------------------
                                         Name:  Donald A. Doering
                                         Title: Authorized Signatory