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                                                                     EXHIBIT 4.6

                                     FORM OF
                                PLEDGE AGREEMENT


       PLEDGE AGREEMENT, dated as of [_______________ ___, _____] (this
"Agreement"), among XO Communications, Inc., a Delaware corporation (the
"Company"), [______________________________], as collateral agent (in such
capacity, together with its successors in such capacity, the "Collateral
Agent"), and [_______________________________________], as Purchase Contract
Agent and as attorney-in-fact of the Holders (as hereinafter defined) from time
to time of the Securities (as hereinafter defined) (in such capacity, together
with its successors in such capacity, the "Purchase Contract Agent") under the
Purchase Contract Agreement (as hereinafter defined).


                                    RECITALS

       The Company and the Purchase Contract Agent are parties to the Purchase
Contract Agreement, dated as of the date hereof (as modified and supplemented
and in effect from time to time, the "Purchase Contract Agreement"), pursuant to
which there will be issued Shares (as defined in the Purchase Contract
Agreement, and as used herein, the "Securities").

       Each Security consists of (a) one Purchase Contract (as hereinafter
defined) and (b) [type and description of underlying securities] ("Underlying
Securities") having a principal amount equal to $__________ (the "Stated
Amount") and maturing on __________, ____ (the "Stock Purchase Date"), subject
to the pledge of such Underlying Securities created hereby.

       Pursuant to the terms of the Purchase Contract Agreement and the Purchase
Contracts, the Holders (as defined in the Purchase Contract Agreement) from time
to time of the Securities have irrevocably authorized the Purchase Contract
Agent, as attorney-in-fact of such Holders, among other things to execute and
deliver this Agreement on behalf of such Holders and to grant the pledge
provided hereby of the Underlying Securities constituting part of such
Securities as provided herein and subject to the terms hereof.

       Accordingly, the Company, the Collateral Agent and the Purchase Contract
Agent, on its own behalf and as attorney-in-fact of the Holders from time to
time of the Securities, agree as follows:

       Section 1.       Definitions. For all purposes of this Agreement, except
as otherwise expressly provided or unless the context otherwise requires:

       (1)    the terms defined in this Article have the meanings assigned to
   them in this Article and include the plural as well as the singular; and

       (2)    the words "herein," "hereof" and "hereunder" and other words of
   similar import refer to this Agreement as a whole and not to any particular
   Article, Section or other subdivision.

       "Act" has the meaning specified in the Purchase Contract Agreement.

       "Agreement" means this instrument as originally executed or as it may
from time to time be supplemented or amended by one or more agreements
supplemental hereto entered into pursuant to the applicable provisions hereof.

      ["Applicable Treasury Regulations" means Subpart O-Book-Entry Procedure of
Title 31 of the Code of Federal Regulations (31 CFR (S) 306.115 et. seq.) and
any other regulations of the United States Treasury Department from time to time
applicable to the transfer or pledge of book-entry U.S. Treasury Securities.]




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       "Business Day" means any day that is not a Saturday, a Sunday or a day on
which the New York Stock Exchange or banking institutions or trust companies in
The City of New York are authorized or obligated by law or executive order to be
closed.

       "Code" has the meaning specified in Section 5(a) hereof.

       "Collateral Agent" has the meaning specified in the first paragraph of
this instrument.

       "Company" means the Person named as the "Company" in the first paragraph
of this instrument until a successor shall have become such, and thereafter
"Company" shall mean such successor.

       "Early Settlement" has the meaning specified in the Purchase Contract
Agreement.

       "Early Settlement Amount" has the meaning specified in the Purchase
Contract Agreement.

       "Holder" when used with respect to a Security, or a Purchase Contract
constituting a part thereof, has the meaning specified in the Purchase Contract
Agreement.

       "Opinion of Counsel" has the meaning specified in the Purchase Contract
Agreement.

       "Outstanding Units" has the meaning specified in the Purchase Contract
Agreement.

       "Outstanding Unit Certificates" has the meaning specified in the Purchase
Contract Agreement.

       "Person" means any individual, corporation, limited liability company,
partnership, joint venture, association, joint-stock company, trust,
unincorporated organization or government or any agency or political subdivision
thereof.

       "Pledge" has the meaning specified in Section 2 hereof.

       "Pledged Securities" has the meaning specified in Section 2
hereof.

       "Purchase Contract" has the meaning specified in the Purchase Contract
Agreement.

       "Purchase Contract Agent" has the meaning specified in the first
paragraph of this instrument.

       "Security" has the meaning specified in the Recitals.

       "Stated Amount" has the meaning specified in the Recitals.

       "Stock Purchase Date" has the meaning specified in the Recitals.

       "Termination Event" has the meaning specified in the Purchase Contract
Agreement.

       "Underlying Securities" has the meaning specified in the Recitals.

       "Unit Certificate" has the meaning specified in the Purchase Contract
Agreement.

       Section 2.       The Pledge. As collateral security for the performance
when due by the Holders from time to time of the Securities of their respective
obligations under the Purchase Contracts constituting part of such Securities,
such Holders acting through the Purchase Contract Agent, as their attorney-in-
fact, hereby pledge and grant to the Collateral Agent, for the benefit of the
Company, a security interest in all of the right, title and interest of such
Holders in the Underlying Securities constituting a part of such Securities.
Prior to or concurrently with the execution and delivery of this Agreement, the
initial Holders shall (i) cause the Underlying Securities to be delivered to the
Collateral Agent [by Federal Reserve Bank-Wire to the account of the Collateral
Agent designated



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by it for such purpose] and (ii) [take appropriate action so that the applicable
Federal Reserve Bank through which such Underlying Securities have been
purchased will reflect such transfer and the Pledge by appropriate entries in
its records in accordance with Applicable Treasury Regulations] [take
appropriate action to reflect such transfer and the Pledge by appropriate
entries in its records]. In addition, the execution and delivery hereof by the
Purchase Contract Agent and the Collateral Agent shall constitute (i) the
notification to the Collateral Agent (as bailee or otherwise) of the Pledge and
(ii) an acknowledgment by the Collateral Agent (as third party in possession or
otherwise) of the Pledge and of its holding of such Underlying Securities
subject to the Pledge, in each case, for purposes of perfecting the Pledge under
[Applicable Treasury Regulations and other] applicable law, including, to the
extent applicable, the Uniform Commercial Code as adopted and in effect in any
applicable jurisdiction. The pledge provided in this Section 2 is herein
referred to as the "Pledge" and the Underlying Securities subject to the Pledge,
excluding any Underlying Securities released from the Pledge as provided in
Section 4 hereof, are hereinafter referred to as the "Pledged Securities."
Subject to the Pledge, the Holders from time to time of the Securities shall
have full beneficial ownership of the Underlying Securities constituting a
part of such Securities.

       Section 3.       Distribution of Principal and Interest. (a) All payments
of principal of, or interest on, any Underlying Securities constituting part of
the Securities received by the Collateral Agent shall be paid by the Collateral
Agent by wire transfer in same day funds no later than ____________, New York
City time on the Business Day such interest payment is received by the
Collateral Agent (provided that in the event such interest payment is received
by the Collateral Agent on a day that is not a Business Day or after
____________, New York City time, on a Business Day, then such payment shall be
made no later than ____________, New York City time, on the next succeeding
Business Day) (i) in the case of (A) interest payments and (B) any principal
payments with respect to any Underlying Securities that have been released from
the Pledge pursuant to Section 4 hereof, to the Purchase Contract Agent to the
account designated by it for such purpose and (ii) in the case of principal
payments on any Pledged Securities, to the Company, in full satisfaction of the
respective obligations of the Holders of the Securities of which such Pledged
Securities are a part under the Purchase Contracts forming a part of such
Securities. All such payments received by the Purchase Contract Agent as
provided herein shall be applied by the Purchase Contract Agent pursuant to the
provisions of the Purchase Contract Agreement. If, notwithstanding the
foregoing, the Purchase Contract Agent shall receive any payments of principal
on account of any Pledged Securities, the Purchase Contract Agent shall hold
the same as trustee of an express trust for the benefit of the Company (and
promptly deliver over to the Company) for application to the obligations of the
Holders of the Securities of which such Underlying Securities are a part under
the Purchase Contracts relating to the Securities of which such Underlying
Securities are a part, and such Holders shall acquire no right, title or
interest in any such payments of principal so received.

       Section 4.       Release of Pledged Securities. (a) Upon
notice to the Collateral Agent by the Company or the Purchase Contract Agent
that there has occurred a Termination Event, the Collateral Agent shall release
all Pledged Securities from the Pledge and shall transfer all such Underlying
Securities, free and clear of any lien, pledge or security interest created
hereby, to the Purchase Contract Agent.

       (b)    Upon notice to the Collateral Agent by the Purchase Contract Agent
that one or more Holders of Securities have elected to effect Early Settlement
of their respective obligations under the Purchase Contracts forming a part of
such Securities in accordance with the terms of the Purchase Contracts and the
Purchase Contract Agreement, and that the Purchase Contract Agent has received
from such Holders, and paid to the Company, the related Early Settlement Amounts
pursuant to the terms of the Purchase Contracts and the Purchase Contract
Agreement and that all conditions to such Early Settlement have been satisfied,
then the Collateral Agent shall release from the Pledge Pledged Securities with
a principal amount equal to the product of (i) the Stated Amount times (ii) the
number of such Purchase Contracts as to which such Holders have elected to
effect Early Settlement.

       (c)    Transfers of Underlying Securities pursuant to Section 4(a) or (b)
shall be by Federal Reserve Bank-Wire or in another appropriate manner, (i) if
the Collateral Agent shall have received such notification at or prior to
____________, New York City time, on a Business Day, then no later than
____________, New York City time, on such Business Day and (ii) if the
Collateral Agent shall have received such notification on a day that is not a
Business Day or after ____________, New York City time, on a Business Day, then
no later than ____________, New York City time, on the next succeeding Business
Day.



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       Section 5.       Rights and Remedies. (a) The Collateral Agent shall
have all of the rights and remedies with respect to the Pledged Securities of a
secured party under the Uniform Commercial Code as in effect in the State of
New York (the "Code") (whether or not said Code is in effect in the
jurisdiction where the rights and remedies are asserted) and such additional
rights and remedies to which a secured party is entitled under the laws in
effect in any jurisdiction where any rights and remedies hereunder may be
asserted.

       (b)    Without limiting any rights or powers otherwise granted by this
Agreement to the Collateral Agent, in the event the Collateral Agent is unable
to make payments to the Company on account of principal payments of any Pledged
Securities as provided in Section 3 hereof in satisfaction of the obligations
of the Holder of the Securities of which such Pledged Securities are a part
under the Purchase Contracts forming a part of such Securities, the Collateral
Agent shall have and may exercise, with reference to such Pledged Securities
and such obligations of such Holder, any and all of the rights and remedies
available to a secured party under the Code after default by a debtor, and as
otherwise granted herein or under any other law.

       (c)    Without limiting any rights or powers otherwise granted by this
Agreement to the Collateral Agent, the Collateral Agent is hereby irrevocably
authorized to receive and collect all payments of principal of or interest on
the Pledged Securities.

       (d)    The Purchase Contract Agent agrees that, from time to time, upon
the written request of the Collateral Agent, the Purchase Contract Agent shall
execute and deliver such further documents and do such other acts and things as
the Collateral Agent may reasonably request in order to maintain the Pledge, and
the perfection and priority thereof, and to confirm the rights of the Collateral
Agent hereunder.

       Section 6.       The Collateral Agent.

       The Collateral Agent and the Company hereby agree between themselves as
follows (it being understood and agreed that neither the Purchase Contract Agent
nor any Holder of Securities shall have any rights under this Section 6):

       6.01   Appointment, Powers and Immunities. The Collateral Agent shall act
as agent for the Company hereunder with such powers as are specifically vested
in the Collateral Agent by the terms of this Agreement, together with such other
powers as are reasonably incidental thereto. The Collateral Agent: (a) shall
have no duties or responsibilities except those expressly set forth in this
Agreement and no implied covenants or obligations shall be inferred from this
Agreement against the Collateral Agent, nor shall the Collateral Agent be bound
by the provisions of any agreement by any party hereto beyond the specific terms
hereof; (b) shall not be responsible to the Company for any recitals contained
in this Agreement, or in any certificate or other document referred to or
provided for in, or received by it under, this Agreement, the Securities or the
Purchase Contract Agreement, or for the value, validity, effectiveness,
genuineness, enforceability or sufficiency of this Agreement (other than as
against the Collateral Agent), the Securities or the Purchase Contract Agreement
or any other document referred to or provided for herein or therein or for any
failure by the Company or any other Person (except the Collateral Agent) to
perform any of its obligations hereunder or thereunder; (c) shall not be
required to initiate or conduct any litigation or collection proceedings
hereunder (except pursuant to directions furnished under Section 6.02 hereof);
(d) shall not be responsible for any action taken or omitted to be taken by it
hereunder or under any other document or instrument referred to or provided for
herein or in connection herewith or therewith, except for its own negligence;
and (e) shall not be required to advise any party as to selling or retaining, or
taking or refraining from taking any action with respect to, any securities or
other property deposited hereunder.

       No provision of this Agreement shall require the Collateral Agent to
expend or risk its own funds or otherwise incur any financial liability in the
performance of any of its duties hereunder. In no event shall the Collateral
Agent be liable for any amount in excess of the value of the Pledged Securities.

       6.02   Instructions of the Company. The Company shall have the right, by
one or more instruments in writing executed and delivered to the Collateral
Agent, to direct the time, method and place of conducting any proceeding for any
right or remedy available to the Collateral Agent, or of exercising any power
conferred on the Collateral Agent, or to direct the taking or refraining from
taking of any action authorized by this


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Agreement; provided, however, that (i) such direction shall not conflict with
the provisions of any law or of this Agreement and (ii) the Collateral Agent
shall be adequately indemnified as provided herein. Nothing in this Section 6.02
shall impair the right of the Collateral Agent in its discretion to take any
action or omit to take any action which it deems proper and which is not
inconsistent with such direction.

       6.03   Reliance by Collateral Agent. The Collateral Agent shall be
entitled to rely upon any certification, order, judgment, opinion, notice or
other communication (including, without limitation, any thereof by telephone,
telecopy, telex, telegram or cable) believed by it to be genuine and correct and
to have been signed or sent by or on behalf of the proper Person or Persons
(without being required to determine the correctness of any fact stated
therein), and upon advice and statements of legal counsel and other experts
selected by the Collateral Agent. As to any matters not expressly provided for
by this Agreement, the Collateral Agent shall in all cases be fully protected in
acting, or in refraining from acting, hereunder in accordance with instructions
given by the Company in accordance with this Agreement.

       6.04   Rights in Other Capacities. The Collateral Agent and its
affiliates may (without having to account therefor to the Company) accept
deposits from, lend money to, make investments in and generally engage in any
kind of banking, trust or other business with the Purchase Contract Agent and
any Holder of Securities (and any of their subsidiaries or affiliates) as if it
were not acting as the Collateral Agent, and the Collateral Agent and its
affiliates may accept fees and other consideration from the Purchase Contract
Agent and any Holder of Securities without having to account for the same to the
Company, PROVIDED that the Collateral Agent covenants and agrees with the
Company that the Collateral Agent shall not accept, receive or permit there to
be created in its favor any security interest, lien or other encumbrance of any
kind in or upon the Pledged Securities.

       6.05   Non-Reliance on Collateral Agent. The Collateral Agent shall not
be required to keep itself informed as to the performance or observance by the
Purchase Contract Agent or any Holder of Securities of this Agreement, the
Purchase Contract Agreement, the Securities or any other document referred to or
provided for herein or therein or to inspect the properties or books of the
Purchase Contract Agent or any Holder of Securities. The Collateral Agent shall
not have any duty or responsibility to provide the Company with any credit or
other information concerning the affairs, financial condition or business of the
Purchase Contract Agent or any Holder of Securities (or any of their affiliates)
that may come into the possession of the Collateral Agent or any of its
affiliates.

       6.06   Compensation and Indemnity. The Company agrees: (i) to pay the
Collateral Agent from time to time reasonable compensation for all services
rendered by its hereunder and (ii) to indemnify the Collateral Agent for, and to
hold it harmless against, any loss, liability or expense incurred without
negligence or bad faith on its part, arising out of or in connection with the
acceptance or administration of its powers and duties under this Agreement,
including the costs and expenses of defending itself against any claim or
liability in connection with the exercise or performance of such powers and
duties.

       6.07   Failure to Act. In the event of any ambiguity in the provisions of
this Agreement or any dispute between or conflicting claims by or among the
undersigned and/or any other person or entity with respect to any funds or
property deposited hereunder, the Collateral Agent shall be entitled, at its
sole option, to refuse to comply with any and all claims, demands or
instructions with respect to such property or funds so long as such dispute or
conflict shall continue, and the Collateral Agent shall not be or become liable
in any way to any of the undersigned for its failure or refusal to comply with
such conflicting claims, demands or instructions. The Collateral Agent shall be
entitled to refuse to act until either (i) such conflicting or adverse claims or
demands shall have been finally determined by a court of competent jurisdiction
or settled by agreement between the conflicting parties as evidenced in a
writing, satisfactory to the Collateral Agent or (ii) the Collateral Agent shall
have received security or an indemnity satisfactory to the Collateral Agent
sufficient to save the Collateral Agent harmless from and against any and all
loss, liability or expense which the Collateral Agent may incur by reason of its
acting. The Collateral Agent may in addition elect to commence an interpleader
action or seek other judicial relief or orders as the Collateral Agent may deem
necessary. Notwithstanding anything contained herein to the contrary, the
Collateral Agent shall not be required to take any action that is in its opinion
contrary to law or to the terms of this Agreement, or which would in its opinion
subject it or any of its officers, employees or directors to liability.

       6.08   Resignation of Collateral Agent. Subject to the appointment and
acceptance of a successor Collateral Agent as provided below, (a) the Collateral
Agent may resign at any time by giving notice


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thereof to the Company and the Purchase Contract Agent, (b) the Collateral Agent
may be removed at any time by the Company and (c) if the Collateral Agent fails
to perform any of its material obligations hereunder in any material respect for
a period of not less than 20 days after receiving notice of such failure by the
Purchase Contract Agent and such failure shall be continuing, the Collateral
Agent may be removed by the Purchase Contract Agent. The Purchase Contract Agent
shall promptly notify the Company of any removal of the Collateral Agent
pursuant to clause (c) of the immediately preceding sentence. Upon any such
resignation or removal, the Company shall have the right to appoint a successor
Collateral Agent. If no successor Collateral Agent shall have been so appointed
and shall have accepted such appointment within 30 days after the retiring
Collateral Agent's giving of notice of resignation or such removal, then the
retiring Collateral Agent may petition any court of competent jurisdiction for
the appointment of a successor Collateral Agent. The Collateral Agent shall be a
bank which has an office in New York, New York with a combined capital and
surplus of at least $50,000,000. Upon the acceptance of any appointment as
Collateral Agent hereunder by a successor Collateral Agent, such successor
Collateral Agent shall thereupon succeed to and become vested with all the
rights, powers, privileges and duties of the retiring Collateral Agent, and the
retiring Collateral Agent shall take all appropriate action to transfer any
money and property held by it hereunder (including the Pledged Securities) to
such successor Collateral Agent. The retiring Collateral Agent shall, upon such
succession, be discharged from its duties and obligations as Collateral Agent
hereunder. After any retiring Collateral Agent's resignation hereunder as
Collateral Agent, the provisions of this Section 6 shall continue in effect for
its benefit in respect of any actions taken or omitted to be taken by it while
it was acting as the Collateral Agent.

       6.09   Right to Appoint Agent or Advisor. The Collateral Agent shall have
the right to appoint agents or advisors in connection with any of its duties
hereunder, and the Collateral Agent shall not be liable for any action taken or
omitted by such agents or advisors selected in good faith.

       6.10   Survival. The provisions of this Section 6 shall survive
termination of this Agreement and the resignation or removal of the Collateral
Agent.

       Section 7.       Amendment.


       7.01   Amendment Without Consent of Holders. Without the consent of any
Holders, the Company, the Collateral Agent and the Purchase Contract Agent, at
any time and from time to time, may amend this Agreement, in form satisfactory
to the Company, the Collateral Agent and the Purchase Contract Agent, for any of
the following purposes:

       (1)    to evidence the succession of another Person to the Company, and
the assumption by any such successor of the covenants of the Company; or

       (2)    to add to the covenants of the Company for the benefit of the
Holders, or to surrender any right or power herein conferred upon the Company;
or

       (3)    to evidence and provide for the acceptance of appointment
hereunder by a successor Collateral Agent or Purchase Contract Agent; or

       (4)    to cure any ambiguity, to correct or supplement any provisions
herein which may be inconsistent with any other such provisions herein, or to
make any other provisions with respect to such matters or questions arising
under this Agreement, provided such action shall not adversely affect the
interests of the Holders.

       7.02   Amendment with Consent of Holders. With the consent of the Holders
of not less than a majority of the Outstanding Units, by Act of said Holders
delivered to the Company, the Agent and the Collateral Agent, the Company, when
authorized by a Board Resolution, the Agent and the Collateral Agent may amend
this Agreement for the purpose of modifying in any manner the provisions of this
Agreement or the rights of the Holders in respect of the Securities; PROVIDED,
HOWEVER, that no such supplemental agreement shall, without the consent of the
Holder of each Outstanding Unit affected thereby,


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       (1)    change the amount or type of Underlying Securities underlying a
Security, impair the right of the Holder of any Security to receive interest
payments on the Underlying Securities or otherwise adversely affect the Holder's
rights in or to such Underlying Securities; or

       (2)    otherwise effect any action that would require the consent of the
Holder of each Outstanding Unit affected thereby pursuant to the Purchase
Contract Agreement if such action were effected by an agreement supplemental
thereto; or

       (3)    reduce the percentage of Outstanding Units the consent of whose
Holders is required for any such amendment.

       It shall not be necessary for any Act of Holders under this Section to
approve the particular form of any proposed amendment, but it shall be
sufficient if such Act shall approve the substance thereof.

       7.03   Execution of Amendments. In executing any amendment permitted by
this Section, the Collateral Agent and the Purchase Contract Agent shall be
entitled to receive and (subject to Section 6.01 hereof, with respect to the
Collateral Agent, and Section 701 of the Purchase Contract Agreement, with
respect to the Purchase Contract Agent) shall be fully protected in relying
upon, an Opinion of Counsel stating that the execution of such amendment is
authorized or permitted by this Agreement.

       7.04   Effect of Amendments. Upon the execution of any amendment under
this Section, this Agreement shall be modified in accordance therewith, and such
amendment shall form a part of this Agreement for all purposes; and every Holder
of Unit Certificates theretofore or thereafter authenticated, executed on behalf
of the Holders and delivered under the Purchase Contract Agreement shall be
bound thereby.

       7.05   Reference to Amendments. Unit Certificates authenticated, executed
on behalf of the Holders and delivered after the execution of any amendment
pursuant to this Section may, and shall if required by the Collateral Agent or
the Purchase Contract Agent, bear a notation in form approved by the Purchase
Contract Agent and the Collateral Agent as to any matter provided for in such
amendment. If the Company shall so determine, new Unit Certificates so modified
as to conform, in the opinion of the Collateral Agent, the Purchase Contract
Agent and the Company, to any such amendment may be prepared and executed by the
Company and authenticated, executed on behalf of the Holders and delivered by
the Purchase Contract Agent in accordance with the Purchase Contract Agreement
in exchange for Outstanding Unit Certificates.

       Section 8.       Miscellaneous.

       8.01   No Waiver. No failure on the part of the Collateral Agent or any
of its agents to exercise, and no course of dealing with respect to, and no
delay in exercising, any right, power or remedy hereunder shall operate as a
waiver thereof; nor shall any single or partial exercise by the Collateral Agent
or any of its agents of any right, power or remedy hereunder preclude any other
or further exercise thereof or the exercise of any other right, power or remedy.
The remedies herein are cumulative and are not exclusive of any remedies
provided by law.

       8.02   Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

       8.03   Notices. All notices, requests, consents and other communications
provided for herein (including, without limitation, any modifications of, or
waivers or consents under, this Agreement) shall be given or



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made in writing (including, without limitation, by telecopy) delivered to the
intended recipient at the "Address for Notices" specified below its name on the
signature pages hereof or, as to any party, at such other address as shall be
designated by such party in a notice to the other parties. Except as otherwise
provided in this Agreement, all such communications shall be deemed to have been
duly given when transmitted by telecopier or personally delivered or, in the
case of a mailed notice, upon receipt, in each case given or addressed as
aforesaid.

       8.04   Successors and Assigns. This Agreement shall be binding upon and
inure to the benefit of the respective successors and assigns of the Company,
the Collateral Agent and the Purchase Contract Agent, and the Holders from time
to time of the Securities, by their acceptance of the same, shall be deemed to
have agreed to be bound by the provisions hereof and to have ratified the
agreements of, and the grant of the Pledge hereunder by, the Purchase Contract
Agent.

       8.05   Counterparts. This Agreement may be executed in any number of
counterparts, all of which taken together shall constitute one and the same
instrument, and any of the parties hereto may execute this Agreement by signing
any such counterpart.

       8.06   Severability. If any provision hereof is invalid and unenforceable
in any jurisdiction, then, to the fullest extent permitted by law, (i) the other
provisions hereof shall remain in full force and effect in such jurisdiction and
shall be liberally construed in order to carry out the intentions of the parties
hereto as nearly as may be possible and (ii) the invalidity or unenforceability
of any provision hereof in any jurisdiction shall not affect the validity or
enforceability of such provision in any other jurisdiction.

       8.07   Expenses, etc. The Company agrees to reimburse the Collateral
Agent for: (a) all reasonable out-of-pocket costs and expenses of the Collateral
Agent (including, without limitation, the reasonable fees and expenses of
counsel to the Collateral Agent), in connection with (i) the negotiation,
preparation, execution and delivery or performance of this Agreement and (ii)
any modification, supplement or waiver of any of the terms of this Agreement;
(b) all reasonable costs and expenses of the Collateral Agent (including,
without limitation, reasonable fees and expenses of counsel) in connection with
(i) any enforcement or proceedings resulting or incurred in connection with
causing any Holder of Securities to satisfy its obligations under the Purchase
Contracts forming a part of the Securities and (ii) the enforcement of this
Section 8.07; and (c) all transfer, stamp, documentary or other similar taxes,
assessments or charges levied by any governmental or revenue authority in
respect of this Agreement or any other document referred to herein and all
costs, expenses, taxes, assessments and other charges incurred in connection
with any filing, registration, recording or perfection of any security interest
contemplated hereby.

       8.08   Security Interest Absolute. All rights of the Collateral Agent and
security interests hereunder, and all obligations of the Holders from time to
time of the Securities hereunder, shall be absolute and unconditional
irrespective of:

              (a)    any lack of validity or enforceability of any provision of
       the Purchase Contracts or the Securities or any other agreement or
       instrument relating thereto;

              (b)    any change in the time, manner or place of payment of, or
       any other term of, or any increase in the amount of, all or any of the
       obligations of Holders of Securities under the related Purchase
       Contracts, or any other amendment or waiver of any term of, or any
       consent to any departure from any requirement of, the Purchase Contract
       Agreement or any Purchase Contract or any other agreement or instrument
       relating thereto; or

              (c)    any other circumstance which might otherwise constitute a
       defense available to, or discharge of, a borrower, a guarantor or a
       pledgor.


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       IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed as of the day and year first above written.

                                     XO COMMUNICATIONS, INC.



                                     By:
                                        ---------------------------------
                                         Name:
                                         Title:

                                     Address for Notices:

                                     11111 Sunset Hills Road
                                     Reston, Virginia 20190
                                     Attention:
                                     Telecopy:  (    ) ___-____


                                     ------------------------------
                                     as Purchase Contract Agent and as
                                     attorney-in-fact of the Holders
                                     from time to time of the Units



                                     By:
                                        ---------------------------------
                                         Name:
                                         Title:

                                     Address for Notices:

                                     [address]
                                     Attention:
                                     Telecopy:  (    ) ___-____




                                     ------------------------------
                                     as Collateral Agent



                                     By:
                                        ---------------------------------
                                         Name:
                                         Title:

                                     Address for Notices:

                                     [address]
                                     Attention:
                                     Telecopy:  (    ) ___-____



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