<PAGE>   1
                                                                     EXHIBIT 4.5

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                             XO COMMUNICATIONS, INC.

                                       AND

                        --------------------------------,
                           as Purchase Contract Agent



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

                           PURCHASE CONTRACT AGREEMENT

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


                           Dated as of ______ __, 200_





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                                TABLE OF CONTENTS

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RECITALS.................................................................................................1

ARTICLE ONE       DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION
Section 101.  Definitions................................................................................1
Section 102.  Form of Documents Delivered to Purchase Contract Agent.....................................7
Section 103.  Acts of Holders; Record Dates..............................................................8
Section 104.  Notices, etc. to Purchase Contract Agent and the Company...................................9
Section 105.  Notice to Holders; Waiver.................................................................10
Section 106.  Effect of Headings and Table of Contents..................................................10
Section 107.  Successors and Assigns....................................................................10
Section 108.  Separability Clause.......................................................................10
Section 109.  Benefits of Agreement.....................................................................10
Section 110.  Governing Law.............................................................................11
Section 111.  Legal Holidays............................................................................11
Section 112.  Counterparts..............................................................................11
Section 113.  Inspection of Agreement...................................................................11

ARTICLE TWO       PURCHASE CONTRACT CERTIFICATE FORMS
Section 201.  Forms of Unit Certificates Generally......................................................11
Section 202.  Form of Purchase Contract Agent's Certificate of Authentication...........................12

ARTICLE THREE     THE UNITS
Section 301.  Title and Terms; Denominations............................................................12
Section 302.  Rights and Obligations Evidenced by the Unit Certificates.................................13
Section 303.  Execution, Authentication, Delivery and Dating............................................13
Section 304.  Temporary Unit Certificates...............................................................14
Section 305.  Registration; Registration of Transfer and Exchange.......................................14
Section 306.  Mutilated, Destroyed, Lost and Stolen Unit Certificates...................................16
Section 307.  Persons Deemed Owners.....................................................................17
Section 308.  Cancellation..............................................................................18
Section 309.  Payments on the Units.....................................................................18

ARTICLE FOUR      THE PLEDGED SECURITIES
Section 401.  Payments on the Pledged Securities........................................................19
Section 402.  Transfer of Pledged Securities Upon Occurrence of Termination Event.......................19
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Section 403.  Transfer of Pledged Securities Upon Early Settlement and Merger Early Settlement..........20

ARTICLE FIVE      THE PURCHASE CONTRACTS
Section 501.  Purchase of Shares........................................................................20
Section 502.  Contract Fees.............................................................................22
Section 503.  Deferral of Payment Dates for Contract Fees...............................................23
Section 504.  Payment of Purchase Price.................................................................23
Section 505.  Issuance of the Shares....................................................................23
[Section 506. Adjustment of Settlement Rate.............................................................24
[Section 507. Notice of Adjustments and Certain Other Events............................................29
Section 508.  No Fractional Shares......................................................................29
Section 509.  Charges and Taxes.........................................................................30
Section 510.  Termination Event; Notice.................................................................30
[Section 511. Early Settlement..........................................................................30
[Section 512. Early Settlement Upon Merger..............................................................32

ARTICLE SIX       REMEDIES
Section 601.  Unconditional Rights of Holders...........................................................33
Section 602.  Restoration of Rights and Remedies........................................................33
Section 603.  Rights and Remedies Cumulative............................................................34
Section 604.  Delay or Omission Not Waiver..............................................................34
Section 605.  Undertaking for Costs.....................................................................34
Section 606.  Waiver of Stay or Extension Laws..........................................................35

ARTICLE SEVEN     THE PURCHASE CONTRACT AGENT
Section 701.  Certain Duties and Responsibilities.......................................................35
Section 702.  Notice of Default.........................................................................36
Section 703.  Certain Rights of Purchase Contract Agent.................................................36
Section 704.  Not Responsible for Recitals or Issuance of Units.........................................37
Section 705.  May Hold Units............................................................................37
Section 706.  Money Held in Trust.......................................................................37
Section 707.  Compensation and Reimbursement............................................................37
Section 708.  Purchase Contract Agent Required; Eligibility.............................................38
Section 709.  Resignation and Removal; Appointment of Successor.........................................38
Section 710.  Acceptance of Appointment by Successor....................................................40
Section 711.  Merger, Conversion, Consolidation or Succession to Business...............................40
Section 712.  Preservation of Information; Communications to Holders....................................41
Section 713.  No Obligations of Purchase Contract Agent.................................................41
Section 714.  Tax Compliance............................................................................41
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ARTICLE EIGHT     SUPPLEMENTAL AGREEMENTS
Section 801.  Supplemental Agreements Without Consent of Holders........................................42
Section 802.  Supplemental Agreements With Consent of Holders...........................................42
Section 803.  Execution of Supplemental Agreements......................................................44
Section 804.  Effect of Supplemental Agreements.........................................................44
Section 805.  Reference to Supplemental Agreements......................................................44

ARTICLE NINE      CONSOLIDATION, MERGER, SALE OR CONVEYANCE
Section 901.  Covenant Not to Merge, Consolidate, Sell or Convey PropertyExcept
              Under Certain Conditions..................................................................44
Section 902.  Rights and Duties of Successor Corporation................................................45
Section 903.  Opinion of Counsel to Purchase Contract Agent.............................................45

ARTICLE TEN       COVENANTS
Section 1001.  Performance Under Purchase Contracts.....................................................46
Section 1002.  Maintenance of Office or Agency..........................................................46
Section 1003.  Company to Reserve Shares................................................................46
Section 1004.  Covenants as to Shares...................................................................47
Section 1005.  Statements of Officers of the Company as to Default......................................47
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TESTIMONIUM.............................................................................................50
SIGNATURES..............................................................................................50
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EXHIBIT A         Form of Unit Certificate
EXHIBIT B         Form of Pledge Agreement


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<PAGE>   6



         PURCHASE CONTRACT AGREEMENT, dated as of _____ __, 200_, between XO
COMMUNICATIONS, INC., a Delaware corporation (the "Company"),
and________________, a __________ corporation, acting as Purchase Contract Agent
for the Holders of Units from time to time (the "Purchase Contract Agent").

                                    RECITALS

         The Company has duly authorized the execution and delivery of this
Agreement and the Unit Certificates evidencing the Units.

         All things necessary to make the Purchase Contracts, when the Unit
Certificates are executed by the Company and authenticated, executed on behalf
of the Holders and delivered by the Purchase Contract Agent, as in this
Agreement provided, the valid obligations of the Company and the Holders, and to
constitute these presents a valid agreement of the Company and the Holders, in
accordance with its terms, have been done.

                                   WITNESSETH:

         For and in consideration of the premises and the entering into of the
Purchase Contracts by the Holders thereof, it is mutually agreed as follows:

                                   ARTICLE ONE

                        DEFINITIONS AND OTHER PROVISIONS
                             OF GENERAL APPLICATION

Section 101.  Definitions.

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

                  (a)      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

                  (b)      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 Section 103.

         "Affiliate" of any specified Person means any other Person directly or
indirectly controlling or controlled by or under direct or indirect common
control with such specified Person. For the purposes of this definition,
"control" when used with respect to any

<PAGE>   7


specified Person means the power to direct the management and policies of such
Person, directly or indirectly, whether through the ownership of voting
securities, by contract or otherwise; and the terms "controlling" and
"controlled" have meanings correlative to the foregoing.

         "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.

         "Average Trading Price" has the meaning specified in Section 501.

         "Board of Directors" means the board of directors of the Company or a
duly authorized committee of that board.

         "Board Resolution" means one or more resolutions of the Board of
Directors, a copy of which has been certified by the Secretary or an Assistant
Secretary of the Company to have been duly adopted by the Board of Directors and
to be in full force and effect on the date of such certification and delivered
to the Purchase Contract Agent.

         "Business Day" means any day other than Saturday, Sunday or any other
day on which banking institutions in The City of New York are authorized or
obligated by law or executive order to be closed.

         "Cash Merger" has the meaning specified in Section 512.

         "Closing Price" has the meaning specified in Section 501.

         "Collateral Agent" means _____________, as Collateral Agent under the
Pledge Agreement, until a successor Collateral Agent shall have become such
pursuant to the applicable provisions of the Pledge Agreement, and thereafter
"Collateral Agent" shall mean the Person who is then the Collateral Agent
thereunder.

         "Collateral Substitution" has the meaning specified in Section 405.

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

         "Contract Fee" means, with respect to each Purchase Contract, a fee
payable by the Company, accruing on the Stated Amount, accruing from and
including the date of first issuance of any Units to but excluding the Stock
Purchase Date and payable quarterly in arrears on each Quarterly Payment Date to
and including the Stock Purchase Date at a rate per annum equal to the Contract
Fee Rate (and computed on



                                      -2-
<PAGE>   8


the basis of a 360-day year of twelve 30-day months), plus any additional fees
accrued thereon pursuant to Section 503.

         "Contract Fee Rate" means ____%.

         "Corporate Trust Office" means the principal office of the Purchase
Contract Agent, at which at any particular time its corporate trust business
shall be administered, which office at the date hereof is located at
_______________.

         "Current Market Price" has the meaning specified in Section 506(a)(8).

         "Depositary" means a clearing agency registered under the Exchange Act
that is designated to act as Depositary for Global Units as contemplated by
Section 305.

         "Early Settlement" has the meaning set forth in Section 511.

         "Early Settlement Amount" has the meaning set forth in Section 511.

         "Early Settlement Date" has the meaning set forth in Section 511.

         "Early Settlement Rate" has the meaning set forth in Section 511.

         "Exchange Act" means the Securities Exchange Act of 1934 or any statute
successor thereto, in each case as amended from time to time.

         "Expiration Date" has the meaning specified in Section 103.

         "Global Unit Certificate" means a Unit Certificate that evidences all
or part of the Units and is registered in the name of the Depositary or a
nominee thereof.

         "Guarantees" means the Company's guarantees of the Notes.

         "Holder" means a Person in whose name a Unit Certificate is registered
in the Unit Register; "Holder", when used with respect to any particular Unit
Certificate (or Unit), means a Person in whose name such Unit Certificate (or
the Unit Certificate evidencing such Unit) is registered in the relevant Unit
Register.

         "Indenture" means the Indenture, dated as of __________ __, ____, among
the Company and ______________, as Trustee, as the same may be amended or
supplemented from time to time with respect to the terms of the Notes in
accordance with the terms thereof.

         "Issuer Order" or "Issuer Request" means a written order or request
signed in the name of the Company by its Chairman of the Board, its Chief
Executive Officer, its President, its Chief Financial Officer, a Vice Chairman
or a Vice President, and by its



                                      -3-
<PAGE>   9


Treasurer, an Assistant Treasurer, its Controller, an Assistant Controller, its
Secretary or an Assistant Secretary, and delivered to the Purchase Contract
Agent.

         "Merger Early Settlement" has the meaning set forth in Section 512.

         "Merger Early Settlement Date" has the meaning set forth in Section
512.

         "NASDAQ" has the meaning specified in Section 501.

         "Notes" means the ______________.

         "Officers' Certificate" means a certificate signed by the Chairman of
the Board, the Chief Executive Officer, the President, the Chief Financial
Officer, a Vice Chairman or a Vice President, and by the Treasurer, an Assistant
Treasurer, the Controller, an Assistant Controller, the Secretary or an
Assistant Secretary of the Company and delivered to the Purchase Contract Agent.

         "Opinion of Counsel" means an opinion in writing signed by legal
counsel, who may be an employee of or counsel to the Company.

         "Outstanding Units" means, as of the date of determination, all Units
evidenced by then Outstanding Unit Certificates, except, on or after the
Termination Date or Stock Purchase Date, Units for which the underlying Pledged
Securities or the Common Stock purchasable upon settlement of the underlying
Purchase Contracts, as the case may be, have been theretofore deposited with the
Purchase Contract Agent in trust for the Holders of such Units; provided,
however, that in determining whether the Holders of the requisite number of
Units have given any request, demand, authorization, direction, notice, consent
or waiver hereunder, Units owned by the Company or any Affiliate of the Company
shall be disregarded and deemed not to be outstanding, except that, in
determining whether the Purchase Contract Agent shall be protected in relying
upon any such request, demand, authorization, direction, notice, consent or
waiver, only Units which the Purchase Contract Agent actually knows to be so
owned shall be so disregarded. Units so owned which have been pledged in good
faith may be regarded as Outstanding Units if the pledgee establishes to the
satisfaction of the Purchase Contract Agent the pledgee's right so to act with
respect to such Units and that the pledgee is not the Company or any Affiliate
of the Company.

         "Outstanding Unit Certificates" means, as of the date of determination,
all Unit Certificates theretofore authenticated, executed and delivered pursuant
to this Agreement, except:

                  (a)      Unit Certificates theretofore canceled by the
         Purchase Contract Agent or delivered to the Purchase Contract Agent for
         cancellation; and

                  (b)      Unit Certificates in exchange for or in lieu of which
         other Unit Certificates have been authenticated and delivered pursuant
         to this Agreement, other than any such Unit Certificate in respect of
         which there shall have been presented to the Purchase Contract Agent
         proof satisfactory to it that such Unit Certificate is held by a bona
         fide purchaser in whose hands the Units evidenced by such Unit
         Certificate are valid obligations of the Company.


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         "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" means the pledge of the Pledged Securities under the Pledge
Agreement.

         "Pledge Agreement" means the Pledge Agreement, dated as of the date
hereof, among the Company, the Collateral Agent and the Purchase Contract Agent,
in its capacity as Purchase Contract Agent and as attorney-in-fact for the
Holders from time to time of the Units, the form of which is attached hereto as
Exhibit B, as the same may be amended from time to time in accordance with the
terms hereof and thereof.

         "Pledged Securities" has the meaning specified in the Pledge Agreement.

         "Predecessor Unit Certificate" of any particular Unit Certificate means
every previous Unit Certificate evidencing all or a portion of the rights and
obligations of the Holder under the Units evidenced thereby; and, for the
purposes of this definition, any Unit Certificate authenticated and delivered
under Section 306 in exchange for or in lieu of a mutilated, destroyed, lost or
stolen Unit Certificate shall be deemed to evidence the same rights and
obligations of the Holder as the mutilated, destroyed, lost or stolen Unit
Certificate.

         "Principal Agreements" means this Agreement (including the obligations
under the Purchase Contracts) and the Pledge Agreement.

         "Purchase Contract" means the obligation of the Company to sell and the
Holder of the related Unit to purchase Shares on the terms and subject to the
conditions set forth in Article Five hereof.

         "Purchase Contract Agent" means the Person named as the "Purchase
Contract Agent" in the first paragraph of this Agreement until a successor
Purchase Contract Agent shall have accepted an appointment as a successor
Purchase Contract Agent pursuant to the applicable provisions of this Agreement,
and thereafter "Purchase Contract Agent" shall mean the Person who is then the
Purchase Contract Agent hereunder.

         "Purchase Contract Settlement Fund" has the meaning specified in
Section 505.


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         "Quarterly Payment Date" means each _________, __________, __________
and __________ commencing _______ __, ____.

         "Record Date", when used with respect to any payment date, means the
Business Day next preceding such payment date.

         "Reorganization Event" has the meaning specified in Section 506(b).

         "Responsible Officer", when used with respect to the Purchase Contract
Agent, means any officer of the Purchase Contract Agent (a) assigned by the
Purchase Contract Agent to administer corporate trust matters and also means,
with respect to a particular corporate trust matter, any other officer to whom
such matter is referred because of his or her knowledge of and familiarity with
the particular subject and (b) who shall have direct responsibility for the
administration of this Agreement.

         "Senior Indebtedness" means indebtedness of the Company of any kind
unless the instrument under which such indebtedness is incurred expressly
provides that it is on parity with or subordinated in right of payment to the
Contract Fees.

         "Settlement Rate" has the meaning specified in Section 501.

         "Shares" means the [Class A Common Stock, par value $.02 per share,]
[Preferred Stock, Series __, par value $.01 per share] of the Company.

         "Stated Amount" means $______ per Unit.

         "Stock Purchase Date" means ________ __, ____ or such earlier date on
which the Purchase Contract may be settled pursuant to Section 511 or Section
512.

         "Termination Date" means the date, if any, on which a Termination Event
occurs.

         "Termination Event" means the occurrence of any of the following events
at any time on or prior to the Stock Purchase Date: (a) the entry by a court
having jurisdiction in the premises of (1) a decree or order for relief in
respect of the Company in an involuntary case or proceeding under any applicable
bankruptcy law or (2) a decree or order adjudging the Company a bankrupt or
insolvent, or approving as properly filed a petition seeking reorganization,
arrangement, adjustment or composition of or in respect of the Company under any
applicable bankruptcy law, or appointing a custodian, receiver, liquidator,
assignee, trustee, sequestrator or other similar official of the Company or of
substantially all of the property of the Company, or ordering the winding up or
liquidation of the affairs of the Company, and the continuance of any decree or
order for relief or any such other decree or order unstayed and in effect for a
period of 90 consecutive days; or (b) the commencement by the Company of a
voluntary case or proceeding under any applicable bankruptcy law, or


                                      -6-
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of any other case or proceeding to be adjudicated a bankrupt or insolvent, or
the consent by the Company to the entry of a decree or order for relief in
respect of the Company in an involuntary case or proceeding under any applicable
bankruptcy law, or to the commencement of any bankruptcy or insolvency case or
proceeding against the Company, or the filing by the Company of a petition or
answer or consent seeking reorganization or relief under any applicable
bankruptcy law, or the consent by the Company to the filing of such petition or
to the appointment of or the taking possession by a custodian, receiver,
liquidator, assignee, trustee, sequestrator or similar official of the Company
or of substantially all or the property of the Company, or the making by the
Company of an assignment for the benefit of creditors, or the admission by the
Company in writing of its inability to pay its debts generally as they become
due, or the taking of corporate action by the Company in furtherance of any such
action.

         "Threshold Appreciation Price" means $____ per Share.

         "TIA" means the Trust Indenture Act of 1939 or any statute successor
thereto, in each case as amended from time to time.

         "Trading Day" has the meaning specified in Section 501.

         "Underwriting Agreement" means the Underwriting Agreement dated _______
__, ____, among the Company, __________ and ____________, as representatives of
the Underwriters named therein.

         "Unit" means the rights to purchase Shares under a Purchase Contract,
together with ownership of the Notes or other Pledged Securities pledged to
secure the obligations owed to the Company under such Purchase Contract, and
subject to the pledge arrangements securing the foregoing obligations. The
Purchase Contracts and/or Pledged Securities constituting a part of any Units
are sometimes referred to herein as "underlying" such Units and are sometimes
herein said to "underlie" such Units.

         "Unit Certificate" means a certificate evidencing the rights and
obligations of a Holder in respect of the number of Units, as the case may be,
specified on such certificate.

         "Unit Register" and "Unit Registrar" have the respective meanings
specified in Section 305.

         "Vice President" means any vice president, whether or not designated by
a number or a word or words added before or after the title "vice president".

Section 102.  Form of Documents Delivered to Purchase Contract Agent.


                                      -7-
<PAGE>   13


         In any case where several matters are required to be certified by, or
covered by an opinion of, any specified Person, it is not necessary that all
such matters be certified by, or covered by the opinion of, only one such
Person, or that they be so certified or covered by only one document, but one
such Person may certify or give an opinion with respect to some matters and one
or more other such Persons as to other matters, and any such Person may certify
or give an opinion as to such matters in one or several documents.

         Any certificate or opinion of an officer of the Company may be based,
insofar as it relates to legal matters, upon a certificate or opinion of, or
representations by, counsel, unless such officer knows, or in the exercise of
reasonable care should know, that the certificate or opinion or representations
with respect to the matters upon which his certificate or opinion is based are
erroneous. Any such certificate or Opinion of Counsel may be based, insofar as
it relates to factual matters, upon a certificate or opinion of, or
representations by, an officer or officers of the Company stating that the
information with respect to such factual matters is in the possession of the
Company, unless such counsel knows, or in the exercise of reasonable care should
know, that the certificate or opinion or representations with respect to such
matters are erroneous.

         Where any Person is required to make, give or execute two or more
applications, requests, consents, certificates, statements, opinions or other
instruments under this Agreement, they may, but need not, be consolidated and
form one instrument.

Section 103.  Acts of Holders; Record Dates.

         (a)      Any request, demand, authorization, direction, notice,
consent, waiver or other action provided by this Agreement to be given or taken
by Holders may be embodied in and evidenced by one or more instruments of
substantially similar tenor signed by such Holders in person or by agent duly
appointed in writing; and, except as herein otherwise expressly provided, such
action shall become effective when such instrument or instruments are delivered
to the Purchase Contract Agent and, where it is hereby expressly required, to
the Company. Such instrument or instruments (and the action embodied therein and
evidenced thereby) are herein sometimes referred to as the "Act" of the Holders
signing such instrument or instruments. Proof of execution of any such
instrument or of a writing appointing any such agent shall be sufficient for any
purpose of this Agreement and (subject to Section 701) conclusive in favor of
the Purchase Contract Agent and the Company, if made in the manner provided in
this Section.

         (b)      The fact and date of the execution by any Person of any such
instrument or writing may be proved by the affidavit of a witness of such
execution or by a certificate of a notary public or other officer authorized by
law to take acknowledgments of deeds, certifying that the individual signing
such instrument or writing acknowledged to him the execution thereof. Where such
execution is by a signer acting in a capacity other than his individual
capacity, such certificate or affidavit shall also constitute sufficient proof
of his


                                      -8-
<PAGE>   14


authority. The fact and date of the execution of any such instrument or writing,
or the authority of the Person executing the same, may also be proved in any
other manner which the Purchase Contract Agent deems sufficient.

         (c)      The ownership of Units shall be proved by the Unit Register.

         (d)      Any request, demand, authorization, direction, notice,
consent, waiver or other Act of the Holder of any Unit shall bind every future
Holder of the same Unit and the Holder of every Unit Certificate evidencing such
Unit issued upon the registration of transfer thereof or in exchange therefor or
in lieu thereof in respect of anything done, omitted or suffered to be done by
the Purchase Contract Agent or the Company in reliance thereon, whether or not
notation of such action is made upon such Unit Certificate.

         (e)      The Company may set any day as a record date for the purpose
of determining the Holders of Outstanding Units entitled to give, make or take
any request, demand, authorization, direction, notice, consent, waiver or other
action provided or permitted by this Agreement to be given, made or taken by
Holders of Units. If any record date is set pursuant to this paragraph, the
Holders of Outstanding Units on such record date, and no other Holders, shall be
entitled to take the relevant action, whether or not such Holders remain Holders
after such record date; provided that no such action shall be effective
hereunder unless taken on or prior to the applicable Expiration Date by Holders
of the requisite number of Outstanding Units on such record date. Nothing in
this paragraph shall be construed to prevent the Company from setting a new
record date for any action for which a record date has previously been set
pursuant to this paragraph (whereupon the record date previously set shall
automatically and with no action by any Person be cancelled and of no effect),
and nothing in this paragraph shall be construed to render ineffective any
action taken by Holders of the requisite number of Outstanding Units on the date
such action is taken. Promptly after any record date is set pursuant to this
paragraph, the Company, at its own expense, shall cause notice of such record
date, the proposed action by Holders and the applicable Expiration Date to be
given to the Purchase Contract Agent in writing and to each Holder of Units in
the manner set forth in Section 105.

         With respect to any record date set pursuant to this Section, the
Company may designate any date as the "Expiration Date" and from time to time
may change the Expiration Date to any earlier or later day; provided that no
such change shall be effective unless notice of the proposed new Expiration Date
is given to the Purchase Contract Agent in writing, and to each Holder of Units
in the manner set forth in Section 105, on or prior to the existing Expiration
Date. If an Expiration Date is not designated with respect to any record date
set pursuant to this Section, the Company shall be deemed to have initially
designated the 180th day after such record date as the Expiration Date with
respect thereto, subject to its right to change the Expiration Date as provided
in this paragraph. Notwithstanding the foregoing, no Expiration Date shall be
later than the 180th day after the applicable record date.



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Section 104.  Notices, etc. to Purchase Contract Agent and the Company.

         Any request, demand, authorization, direction, notice, consent, waiver
or other Act of Holders or other document provided or permitted by this
Agreement to be made upon, given or furnished to, or filed with,

                  (a)      the Purchase Contract Agent by any Holder or by the
         Company shall be (unless otherwise herein expressly provided) made,
         given, furnished or filed in writing and personally delivered or
         mailed, first-class postage prepaid, or sent by facsimile to the
         Purchase Contract Agent's Corporate Trust Office, Attention:
         ____________, or at any other address previously furnished in writing
         by the Purchase Contract Agent to the Holders and the Company, and
         shall be deemed to have been duly given upon receipt by the Purchase
         Contract Agent, or

                  (b)      the Company by the Purchase Contract Agent or by any
         Holder shall be sufficient for every purpose hereunder (unless
         otherwise herein expressly provided) if made, given, furnished or filed
         in writing and personally delivered or mailed, first-class postage
         prepaid, to the Company at 11111 Sunset Hills Drive, Reston, Virginia
         20190, Attention: _________, or at any other address previously
         furnished in writing by the Company to the Purchase Contract Agent.

Section 105.  Notice to Holders; Waiver.

         Except as otherwise provided, where this Agreement provides for notice
to Holders of any event, such notice shall be sufficiently given (unless
otherwise herein expressly provided) if in writing and mailed, first-class
postage prepaid, to each Holder affected by such event, at his address as it
appears in the Unit Register, not later than the latest date, and not earlier
than the earliest date, prescribed for the giving of such notice. In any case
where notice to Holders is given by mail, neither the failure to mail such
notice nor any defect in any notice so mailed to any particular Holder shall
affect the sufficiency of such notice with respect to other Holders. Where this
Agreement provides for notice in any manner, such notice may be waived in
writing by the Person entitled to receive such notice, either before or after
the event, and such waiver shall be the equivalent of such notice. Waivers of
notice by Holders shall be filed with the Purchase Contract Agent, but such
filing shall not be a condition precedent to the validity of any action taken in
reliance upon such waiver.

         In case by reason of the suspension of regular mail service or by
reason of any other cause it shall be impracticable to give such notice by mail,
then such notification as shall be made with the approval of the Purchase
Contract Agent shall constitute a sufficient notification for every purpose
hereunder.

Section 106.  Effect of Headings and Table of Contents.


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<PAGE>   16

         The Article and Section headings herein and the Table of Contents are
for convenience only and shall not affect the construction hereof.

Section 107.  Successors and Assigns.

         All covenants and agreements in this Agreement by the Company shall
bind its successors and assigns, whether so expressed or not.

Section 108.  Separability Clause.

         In case any provision in this Agreement or in the Units shall be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions hereof and thereof shall not in any way be affected or
impaired thereby.

Section 109.  Benefits of Agreement.

         Nothing in this Agreement or in the Unit Certificates, express or
implied, shall give to any Person, other than the parties hereto and their
successors hereunder and the Holders, any benefits or any legal or equitable
right, remedy or claim under this Agreement. The Holders from time to time shall
be beneficiaries of this Agreement and shall be bound by all of the terms and
conditions hereof and of the Units evidenced by their Unit Certificates by their
acceptance of delivery thereof.

Section 110.  Governing Law.

         THIS AGREEMENT AND THE UNITS SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO CONFLICTS
OF LAWS PRINCIPLES THEREOF.

Section 111.  Legal Holidays.

         In any case where any Quarterly Payment Date or the Stock Purchase Date
shall not be a Business Day, then (notwithstanding any other provision of this
Agreement or of the Units) payment in respect of distributions or interest on or
principal of Pledged Securities or Contract Fees shall not be made, Purchase
Contracts shall not be performed and other actions described herein shall not
occur, but such payments shall be made, the Purchase Contracts shall be
performed and such other actions shall occur, as applicable, on the next
succeeding Business Day with the same force and effect as if made on such
Quarterly Payment Date or Stock Purchase Date, as the case may be; provided,
that to the extent such payment is made on the next succeeding Business Day, no
distributions or interest shall accrue or be payable by the Company or any
Holder for the period from and after any such Quarterly Payment Date or Stock
Purchase Date, as the case may be, to the date of payment


                                      -11-
<PAGE>   17


or performance; except that if such next succeeding Business Day is in the next
succeeding calendar year, such payment shall be made, the Purchase Contracts
shall be performed or such other action shall occur on the immediately preceding
Business Day with the same force and effect as if made on such Quarterly Payment
Date or the Stock Purchase Date.

Section 112.  Counterparts.

         This Agreement may be executed in any number of counterparts, each of
which, when so executed, shall be deemed an original, but all such counterparts
shall together constitute one and the same instrument.

Section 113.  Inspection of Agreement.

         A copy of this Agreement shall be available at all reasonable times at
the Corporate Trust Office for inspection by any Holder.

                                   ARTICLE TWO

                       PURCHASE CONTRACT CERTIFICATE FORMS

Section 201.  Forms of Unit Certificates Generally.

         Unit Certificates evidencing Units shall be in substantially the form
set forth in Exhibit A hereto, with such letters, numbers or other marks of
identification or designation and such legends or endorsements printed,
lithographed or engraved thereon as may be required by the rules of any
securities exchange on which the Units are listed or Depositary therefor, or as
may, consistently herewith, be determined by the officers of the Company
executing such Unit Certificates, as evidenced by their execution of the Unit
Certificates.

         The definitive Unit Certificates shall be printed, lithographed or
engraved on steel engraved borders or may be produced in any other manner, all
as determined by the officers of the Company executing the Unit Certificates,
consistent with the provisions of this Agreement, as evidenced by their
execution thereof.

         Every Global Unit Certificate authenticated, executed and delivered
hereunder shall bear a legend in substantially the following form:

         THIS UNIT CERTIFICATE IS A GLOBAL UNIT CERTIFICATE WITHIN THE MEANING
         OF THE PURCHASE CONTRACT AGREEMENT HEREINAFTER REFERRED TO AND IS
         REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF. THIS UNIT
         CERTIFICATE MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR A UNIT
         CERTIFICATE REGISTERED, AND NO TRANSFER OF THIS UNIT CERTIFICATE IN
         WHOLE OR IN PART MAY BE REGISTERED, IN THE


                                      -12-
<PAGE>   18

         NAME OF ANY PERSON OTHER THAN SUCH DEPOSITARY OR A NOMINEE THEREOF,
         EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE PURCHASE CONTRACT
         AGREEMENT.

Section 202.  Form of Purchase Contract Agent's Certificate of Authentication.

         The form of the Purchase Contract Agent's certificate of authentication
for the Units shall be in substantially the form set forth on the form of the
Unit Certificates.

                                  ARTICLE THREE

                                    THE UNITS

Section 301.  Title and Terms; Denominations.

         The aggregate number of Units evidenced by Unit Certificates
authenticated, executed on behalf of the Holders and delivered hereunder is
limited to _________ [(subject to increase up to a maximum of _______ to the
extent the over-allotment option of the underwriters under the Underwriting
Agreement is exercised)], except for Unit Certificates authenticated, executed
and delivered upon registration of transfer of, in exchange for, or in lieu of,
other Unit Certificates pursuant to Sections 304, 305, 306 or 805.

         Unit Certificates shall be issuable only in registered form and only in
denominations of a single Unit and any integral multiple thereof.

Section 302.  Rights and Obligations Evidenced by the Unit Certificates.

         Each Unit Certificate shall evidence the number of Units specified
therein. Prior to the purchase, if any, of Shares under the Purchase Contracts,
the Units shall not entitle the Holders to any of the rights or privileges of a
holder of Shares by virtue of holding such Units, including, without limitation,
the right to vote or receive any dividends or other distributions or to consent
or to receive notice as stockholders in respect of the meetings of stockholders
or for the election of directors of the Company or for any other matter.

Section 303.  Execution, Authentication, Delivery and Dating.

         Subject to the provisions of Section 309 hereof, upon the execution and
delivery of this Agreement, and at any time and from time to time thereafter,
the Company may deliver Unit Certificates executed by the Company to the
Purchase Contract Agent for authentication, execution on behalf of the Holders
and delivery, together with its Issuer Order for authentication of such Unit
Certificates, and the Purchase Contract Agent in accordance with such Issuer
Order shall authenticate, execute on behalf of the Holders and make such Unit
Certificates available for delivery.


                                      -13-
<PAGE>   19


         The Unit Certificates shall be executed on behalf of the Company by its
Chairman of the Board, its Chief Executive Officer, its President, its Chief
Financial Officer or one of its Vice Presidents, under its corporate seal
reproduced thereon attested by its Secretary or one of its Assistant
Secretaries. The signature of any of these officers on the Unit Certificates may
be manual or facsimile.

         Unit Certificates bearing the manual or facsimile signatures of
individuals who were at any time the proper officers of the Company shall bind
the Company, notwithstanding that such individuals or any of them have ceased to
hold such offices prior to the authentication and delivery of such Unit
Certificates or did not hold such offices at the date of such Unit Certificates.

         Each Unit Certificate shall be dated the date of its authentication.

         No Purchase Contract evidenced by a Unit Certificate shall be valid
until such Unit Certificate has been executed on behalf of the Holder by the
manual signature of an authorized signatory of the Purchase Contract Agent, as
such Holder's attorney-in-fact. Such signature by an authorized signatory of the
Purchase Contract Agent shall be conclusive evidence that the Holder of such
Unit Certificate has entered into the Purchase Contracts evidenced by such Unit
Certificate.

         No Unit Certificate shall be entitled to any benefit under this
Agreement or be valid or obligatory for any purpose unless there appears on such
Unit Certificate a certificate of authentication substantially in the form
provided for herein executed by an authorized signatory of the Purchase Contract
Agent by manual signature, and such certificate upon any Unit Certificate shall
be conclusive evidence, and the only evidence, that such Unit Certificate has
been duly authenticated and delivered hereunder.

Section 304.  Temporary Unit Certificates.

         Pending the preparation of definitive Unit Certificates, the Company
shall execute and deliver (together with an Issuer Order) to the Purchase
Contract Agent, and the Purchase Contract Agent shall authenticate, execute on
behalf of the Holders, and deliver, in lieu of such definitive Unit
Certificates, temporary Unit Certificates which are in substantially the form
set forth in Exhibit A hereto, with such letters, numbers or other marks of
identification or designation and such legends or endorsements printed,
lithographed or engraved thereon as may be required by the rules of any
securities exchange on which the Units are listed or Depositary therefor, or as
may, consistently herewith, be determined by the officers of the Company
executing such Unit Certificates, as evidenced by their execution of the Unit
Certificates.


                                      -14-
<PAGE>   20

         If temporary Unit Certificates are issued, the Company will cause
definitive Unit Certificates to be prepared without unreasonable delay. After
the preparation of definitive Unit Certificates, the temporary Unit Certificates
shall be exchangeable for definitive Unit Certificates upon surrender of the
temporary Unit Certificates at the Corporate Trust Office, at the expense of the
Company and without charge to the Holder. Upon surrender for cancellation of any
one or more temporary Unit Certificates, the Company shall execute and deliver
to the Purchase Contract Agent, and the Purchase Contract Agent shall
authenticate, execute on behalf of the Holder, and deliver in exchange therefor,
one or more definitive Unit Certificates of authorized denominations and
evidencing a like number of Units, as the case may be, as the temporary Unit
Certificate or Unit Certificates so surrendered. Until so exchanged, the
temporary Unit Certificates shall in all respects evidence the same benefits and
the same obligations with respect to the Units evidenced thereby as definitive
Unit Certificates.

Section 305.  Registration; Registration of Transfer and Exchange.

         The Purchase Contract Agent shall keep at the Corporate Trust Office
registers (the registers maintained in such office being herein referred to as
the "Unit Registers") in which, subject to such reasonable regulations as it may
prescribe, the Purchase Contract Agent shall provide for the registration of
Unit Certificates evidencing the Units and of transfers of Unit Certificates
evidencing Units (the Purchase Contract Agent, in such capacity, the "Unit
Registrar"). Upon request from any Trustee or the Company, the Purchase Contract
Agent shall furnish to such requesting party a copy of the Unit Register for the
Unit Certificates evidencing the Units as promptly as practicable.

         Upon surrender for registration of transfer of any Unit Certificate at
the Corporate Trust Office, the Company shall execute and deliver to the
Purchase Contract Agent, and the Purchase Contract Agent shall authenticate,
execute on behalf of the designated transferee or transferees, and deliver, in
the name of the designated transferee or transferees, one or more new Unit
Certificates evidencing a like number of Units.

         At the option of the Holder, Unit Certificates may be exchanged for
other Unit Certificates evidencing a like number of Units upon surrender of the
Unit Certificates to be exchanged at the Corporate Trust Office. Whenever any
Unit Certificates are so surrendered for exchange, the Company shall execute and
deliver to the Purchase Contract Agent, and the Purchase Contract Agent shall
authenticate, execute on behalf of the Holder, and deliver the Unit Certificates
which the Holder making the exchange is entitled to receive.

         All Unit Certificates issued upon any registration of transfer or
exchange of a Unit Certificate shall evidence the ownership of the same number
of Units, and be entitled to the same benefits and subject to the same
obligations, under the Principal Agreements as the Units, evidenced by the Unit
Certificate surrendered upon such registration of transfer or exchange.


                                      -15-
<PAGE>   21


         Every Unit Certificate presented or surrendered for registration of
transfer or for exchange shall (if so required by the Purchase Contract Agent)
be duly endorsed, or be accompanied by a written instrument of transfer in form
satisfactory to the Company and the Purchase Contract Agent duly executed, by
the Holder thereof or his attorney duly authorized in writing.

         No service charge shall be made for any registration of transfer or
exchange of a Unit Certificate, but the Company and the Purchase Contract Agent
may require payment from the Holder of a sum sufficient to cover any tax or
other governmental charge that may be imposed in connection with any
registration of transfer or exchange of Unit Certificates, other than any
exchanges pursuant to Sections 304, 306 and 805 not involving any transfer.

         Notwithstanding the foregoing, the Company shall not be obligated to
execute and deliver to the Purchase Contract Agent, and the Purchase Contract
Agent shall not be obligated to authenticate, execute on behalf of the Holder
and deliver any Unit Certificate in respect of a Unit Certificate presented or
surrendered for registration of transfer or for exchange on or after the Stock
Purchase Date or the Termination Date. In lieu of delivery of a new Unit
Certificate, upon satisfaction of the applicable conditions specified above in
this Section and receipt of appropriate registration or transfer instructions
from such Holder, the Purchase Contract Agent shall (a) if the Stock Purchase
Date has occurred, deliver the Shares issuable in respect of the Purchase
Contracts forming a part of the Units evidenced by such Unit Certificate, or (b)
if a Termination Event shall have occurred on or prior to the Stock Purchase
Date, transfer the liquidation or principal amount of the Pledged Securities
evidenced thereby, in each case subject to the applicable conditions and in
accordance with the applicable provisions of Article Five hereof.

         The provisions of Clauses (a), (b), (c) and (d) below shall apply only
to Global Unit Certificates:

                  (a)      Each Global Unit Certificate authenticated and
         executed on behalf of the Holders under this Agreement shall be
         registered in the name of the Depositary designated for such Global
         Unit Certificate or a nominee thereof and delivered to such Depositary
         or a nominee thereof or custodian therefor, and each such Global Unit
         Certificate shall constitute a single Unit Certificate for all purposes
         of this Agreement.

                  (b)      Notwithstanding any other provision in this
         Agreement, no Global Unit Certificate may be exchanged in whole or in
         part for Unit Certificates registered, and no transfer of a Global Unit
         Certificate in whole or in part may be registered, in the name of any
         Person other than the Depositary for such Global Unit Certificate or a
         nominee thereof unless (i) such Depositary (x) has notified the Company
         that it is unwilling or unable to continue as Depositary for such
         Global Unit Certificate or


                                      -16-
<PAGE>   22


         (y) has ceased to be a clearing agency registered under the Exchange
         Act or (ii) there shall have occurred and be continuing a default by
         the Company in respect of its obligations under one or more Principal
         Agreements.

                  (c)      Subject to Clause (b) above, any exchange of a Global
         Unit Certificate for other Unit Certificates may be made in whole or in
         part, and all Unit Certificates issued in exchange for a Global Unit
         Certificate or any portion thereof shall be registered in such names as
         the Depositary for such Global Unit Certificate shall direct.

                  (d)      Every Unit Certificate authenticated and delivered
         upon registration of transfer of, in exchange for or in lieu of a
         Global Unit Certificate or any portion thereof, whether pursuant to
         this Section, Section 304, 306 or 805 or otherwise, shall be
         authenticated, executed on behalf of the Holders and delivered in the
         form of, and shall be, a Global Unit Certificate, unless such Unit
         Certificate is registered in the name of a Person other than the
         Depositary for such Global Unit Certificate or a nominee thereof.

Section 306.  Mutilated, Destroyed, Lost and Stolen Unit Certificates.

         If any mutilated Unit Certificate is surrendered to the Purchase
Contract Agent, the Company shall execute and deliver to the Purchase Contract
Agent, and the Purchase Contract Agent shall authenticate, execute on behalf of
the Holder, and deliver in exchange therefor, a new Unit Certificate, evidencing
the same number of Units and bearing a number not contemporaneously outstanding.

         If there shall be delivered to the Company and the Purchase Contract
Agent (a) evidence to their satisfaction of the destruction, loss or theft of
any Unit Certificate, and (b) such security or indemnity as may be required by
them to save each of them and any agent of any of them harmless, then, in the
absence of notice to the Company or the Purchase Contract Agent that such Unit
Certificate has been acquired by a bona fide purchaser, the Company shall
execute and deliver to the Purchase Contract Agent, and the Purchase Contract
Agent shall authenticate, execute on behalf of the Holder, and deliver to the
Holder, in lieu of any such destroyed, lost or stolen Unit Certificate, a new
Unit Certificate, evidencing the same number of Units and bearing a number not
contemporaneously outstanding.

         Notwithstanding the foregoing, the Company shall not be obligated to
execute and deliver to the Purchase Contract Agent, and the Purchase Contract
Agent shall not be obligated to authenticate, execute on behalf of the Holder,
and deliver to the Holder, on or after the Stock Purchase Date or the
Termination Date, a Unit Certificate in respect of any mutilated, destroyed,
lost or stolen Unit Certificate. In lieu of delivery of a new Unit Certificate,
upon satisfaction of the applicable conditions specified above in this Section
and


                                      -17-
<PAGE>   23


receipt of appropriate registration or transfer instructions from such Holder,
the Purchase Contract Agent shall (a) if the Stock Purchase Date has occurred,
deliver the Shares issuable in respect of the Purchase Contracts forming a part
of the Units evidenced by such Unit Certificate, or (b) if a Termination Event
shall have occurred on or prior to the Stock Purchase Date, transfer the
liquidation or principal amount of the Pledged Securities evidenced thereby, in
each case subject to the applicable conditions and in accordance with the
applicable provisions of Article Five hereof.

         Upon the issuance of any new Unit Certificate under this Section, the
Company and the Purchase Contract Agent may require the payment by the Holder of
a sum sufficient to cover any tax or other governmental charge that may be
imposed in relation thereto and any other expenses (including the fees and
expenses of the Purchase Contract Agent) connected therewith.

         Every new Unit Certificate issued pursuant to this Section in lieu of
any destroyed, lost or stolen Unit Certificate shall constitute an original
additional contractual obligation of the Company and of the Holder, whether or
not the destroyed, lost or stolen Unit Certificate shall be at any time
enforceable by anyone, and shall be entitled to all the benefits and be subject
to all the obligations of the Principal Agreements equally and proportionately
with any and all other Unit Certificates delivered hereunder.

         The provisions of this Section are exclusive and shall preclude (to the
extent lawful) all other rights and remedies with respect to the replacement or
settlement of mutilated, destroyed, lost or stolen Unit Certificates.

Section 307.  Persons Deemed Owners.

         Prior to due presentment of a Unit Certificate for registration of
transfer, the Company and the Purchase Contract Agent, and any agent of the
Company or the Purchase Contract Agent, may treat the Person in whose name such
Unit Certificate is registered as the owner of the Units evidenced thereby, for
the purpose of receiving payments of Contract Fees, distributions or interest on
the Pledged Securities and performance of the underlying Purchase Contracts and
for all other purposes whatsoever, whether or not the payment of Contract Fees,
distributions or interest on the Pledged Securities payable in respect of the
Purchase Contracts constituting a part of the Units evidenced thereby shall be
overdue and notwithstanding any notice to the contrary, and neither the Company
nor the Purchase Contract Agent, nor any agent of the Company or the Purchase
Contract Agent, shall be affected by notice to the contrary.

         Notwithstanding the foregoing, with respect to any Global Unit
Certificate, nothing herein shall prevent the Company, the Purchase Contract
Agent or any agent of the Company or the Purchase Contract Agent, from giving
effect to any written certification, proxy or other authorization furnished by
any Depositary (or its nominee), as a Holder, with respect to such


                                      -18-
<PAGE>   24


Global Unit Certificate or impair, as between such Depositary and owners of
beneficial interests in such Global Unit Certificate, the operation of customary
practices governing the exercise of rights of such Depositary (or its nominee)
as Holder of such Global Unit Certificate.

Section 308.  Cancellation.

         All Unit Certificates surrendered for delivery of Shares on or after
the Stock Purchase Date, transfer of Pledged Securities after the occurrence of
a Termination Event or registration of transfer or exchange shall, if
surrendered to any Person other than the Purchase Contract Agent, be delivered
to the Purchase Contract Agent and, if not already canceled, shall be promptly
canceled by it. The Company may at any time deliver to the Purchase Contract
Agent for cancellation any Unit Certificates previously authenticated, executed
and delivered hereunder which the Company may have acquired in any manner
whatsoever, and all Unit Certificates so delivered shall, upon Issuer Order, be
promptly canceled by the Purchase Contract Agent. No Unit Certificates shall be
authenticated, executed on behalf of the Holder and delivered upon transfer of,
in exchange for or in lieu of any Unit Certificates canceled as provided in this
Section, except as expressly permitted by this Agreement. All canceled Unit
Certificates held by the Purchase Contract Agent shall be disposed of as
directed by Issuer Order; [provided, however, that the Purchase Contract Agent
shall not be required to destroy such Unit Certificates].

         If the Company or any Affiliate of the Company shall acquire any Unit
Certificate, such acquisition shall not operate as a cancellation of such Unit
Certificate unless and until such Unit Certificate is delivered to the Purchase
Contract Agent canceled or for cancellation.

Section 309.  Payments on the Units.

         All amounts payable to Holders as required by Section 401, will be
payable at the office of the Purchase Contract Agent in The City of New York
maintained for that purpose or, at the option of the Company, by check mailed to
the address of the Person entitled thereto at such address as it appears on the
relevant Unit Register on the Record Date; provided, however, that for so long
as any Units are evidenced by Global Certificates, the Purchase Contract Agent
will pay each such amount payable in respect of such Units by wire transfer in
same-day funds, no later than 2:00 p.m., New York City time, on the Business Day
such amount is received by the Purchase Contract Agent from the Collateral Agent
or the Company (or, if such amount is received by the Purchase Contract Agent
after 1:00 p.m., New York City time, on a Business Day or on a day that is not a
Business Day, no later than 10:00 a.m., New York City time, on the next
succeeding Business Day), to the Depositary, to the account or accounts
designated by it for such purpose.


                                      -19-
<PAGE>   25


                                  ARTICLE FOUR

                             THE PLEDGED SECURITIES

Section 401.  Payments on the Pledged Securities.

         Interest on any Pledged Security that is paid on any Quarterly Payment
Date shall, subject to receipt thereof by the Purchase Contract Agent from the
Collateral Agent as provided by the terms of the Pledge Agreement, be paid to
the Person in whose name the Unit Certificate (or one or more Predecessor Unit
Certificates) of which such Pledged Security is a part is registered at the
close of business on the Record Date next preceding such Quarterly Payment Date.

         Each Unit Certificate evidencing Pledged Securities delivered under
this Agreement upon registration of transfer of or in exchange for or in lieu of
any other Unit Certificate shall carry the rights to interest accrued and
unpaid, and to accrue, which were carried by the Pledged Securities underlying
such other Unit Certificate.

         In the case of any Unit with respect to which Early Settlement of the
underlying Purchase Contract is effected on an Early Settlement Date after any
Record Date and on or prior to the next succeeding Quarterly Payment Date,
interest on the Pledged Securities underlying such Unit otherwise payable on
such Quarterly Payment Date shall be payable on such Quarterly Payment Date
notwithstanding such Early Settlement, and such interest shall, subject to
receipt thereof by the Purchase Contract Agent, be paid to the Person in whose
name the Unit Certificate (or one or more Predecessor Unit Certificates) is
registered at the close of business on the Record Date.  Except as otherwise
expressly provided in the immediately preceding sentence, in the case of any
Unit with respect to which Early Settlement of the underlying Purchase Contract
is effected on an Early Settlement Date, interest on the related Pledged
Securities that would otherwise be payable after the Early Settlement Date shall
not be payable hereunder to the Holder of such Security.

Section 402.  Transfer of Pledged Securities Upon Occurrence of Termination
              Event.

         Upon the occurrence of a Termination Event and the transfer of the
Pledged Securities underlying each Holder's Units to the Purchase Contract Agent
pursuant to the terms of the Pledge Agreement, the Purchase Contract Agent shall
request transfer instructions with respect to such Pledged Securities from such
Holder by written request mailed to such Holder at his address as it appears in
the relevant Unit Register and shall give notice of such Termination Event to
the Collateral Agent. Thereafter, upon surrender to the Purchase Contract Agent
of a Unit Certificate evidencing a Holder's Units, with transfer instructions in
proper form for transfer of the underlying Pledged Securities, the Purchase
Contract Agent shall transfer the Pledged Securities evidenced by such Unit
Certificate to such Holder in accordance with such instructions; provided,
however, that if the Pledged Securities are to be transferred to a Person other
than the Person in whose name such Unit Certificate is registered, no such
transfer shall be made unless the Person requesting the transfer has paid any
transfer and other taxes required by reason of such transfer to a Person other
than the registered Holder of such Unit Certificate or has established to the
satisfaction of the Company that such tax either has been paid or is not
payable. Until the foregoing conditions to transfer any of the Pledged
Securities underlying any Units has been met, the Purchase Contract Agent shall
hold such Pledged Securities as custodian for the Holder of such Units.

         If upon a Termination Event any Holder of Units would, after satisfying
the foregoing conditions, otherwise be entitled to receive (or have transferred
to such Holder's designee) treasury securities of any series having a principal
amount that is not an integral multiple of $1,000, such Holder shall instead be
entitled to receive (or have transferred to


                                      -20-
<PAGE>   26



such Holder's designee) treasury securities of such series in a principal amount
equal to the next lower integral multiple of $1,000 plus a portion of the net
proceeds from the sale of treasury securities of such series contemplated by the
succeeding sentence representing such Holder's interest therein. As soon as
practicable after transfer to the Purchase Contract Agent of the Pledged
Securities as provided in the Pledge Agreement, the Purchase Contract Agent
shall, at the direction and on behalf of all Holders who, by virtue of the
preceding sentence, will not be entitled to a portion of the treasury securities
of any series to which they would otherwise be entitled, aggregate and sell the
treasury securities of such series representing such portion to or through one
or more U.S. government securities dealers at then prevailing prices, deduct
from the proceeds of such sales all commissions and other out-of-pocket
transaction costs incurred in connection with such sales and, until the net
proceeds therefrom have been distributed to the Holders entitled thereto or
their designees, hold such proceeds in trust for such Holders.

Section 403. Transfer of Pledged Securities Upon Early Settlement and Merger
Early Settlement.

         (a)      In the event of Early Settlement as described in Section 511,
the Pledged Securities with respect to all Units which have been presented for
settlement shall be released by the Collateral Agent to the Purchase Contract
Agent who shall deliver the Pledged Securities to the Holder upon satisfaction
of the conditions precedent described in Section 511.

         (b)      In the event of a Cash Merger as described in Section 512, the
Pledged Securities with respect to all Units which have been presented for
payment on the Merger Early Settlement Date shall be released by the Collateral
Agent to the Purchase Contract Agent who shall deliver the Pledged Securities to
the Unit Holder upon satisfaction of the conditions precedent described in
Section 512.

                                  ARTICLE FIVE

                             THE PURCHASE CONTRACTS

Section 501.  Purchase of Shares.

         Each Holder of a Unit Certificate, by its acceptance thereof, agrees
that it has entered into and shall be bound by the underlying Purchase Contract
the terms and conditions of which are set forth in this Article Five. Each
Purchase Contract shall obligate the Holder of such Unit to purchase, and the
Company to sell, on the Stock Purchase Date, at a price equal to the Stated
Amount, a number of shares of Common Stock equal to the Settlement Rate, unless,
on or prior to the Stock Purchase Date, there shall have occurred a Termination
Event. The "Settlement Rate" is equal to [(a) if the Average Trading Price (as
defined below) is greater than or equal to the Threshold Appreciation Price,
_______ of a Share per



                                      -21-
<PAGE>   27


Purchase Contract, (b) if the Average Trading Price is less than the Threshold
Appreciation Price but is greater than the Stated Amount, a fractional share of
a Share per Purchase Contract equal to the Stated Amount divided by the Average
Trading Price (rounded upward or downward to the nearest 1/10,000th of a share
or, if there is not a nearest 1/10,000th of a share, to the next lower
1/10,000th of a share) and (c) if the Average Trading Price is less than or
equal to the Stated Amount, one Share per Purchase Contract, in each case
subject to adjustment as provided in Section 506] [provide alternative for
Preferred Stock]. As provided in Section 508, no fractional Shares will be
issued upon settlement of Purchase Contracts.

         [The Average Trading Price means the average of the Closing Prices per
Share on each of the twenty consecutive Trading Days ending on the last Trading
Day immediately preceding the Stock Purchase Date. The "Closing Price" of the
Shares on any date of determination means the closing sale price (or, if no
closing price is quoted, the last quoted sale price) of the Shares on the NASDAQ
National Market ( "NASDAQ") on such date or, if the Shares are not quoted on
NASDAQ on any such date, as reported in the composite transactions for the
principal United States securities market on which the Shares are so quoted or,
if the Shares are not so quoted on a United States national or regional
securities market, the last quoted bid price for the Shares in the
over-the-counter market as reported by the National Quotation Bureau or similar
organization or, if such bid price is not available, the market value of the
Shares on such date as determined by a nationally recognized investment banking
firm retained for this purpose by the Company. A "Trading Day" means a day on
which the Shares (A) are not suspended from trading on any national or regional
securities exchange or association or over-the-counter market at the close of
business and (B) have traded at least once on the national or regional
securities exchange or association or over-the-counter market that is the
primary market for the trading of the Shares.]

         Each Holder of a Unit Certificate evidencing Units, by its acceptance
thereof, irrevocably authorizes the Purchase Contract Agent to enter into and
perform the underlying Purchase Contracts on its behalf as its attorney-in-fact,
agrees to be bound by the terms and provisions thereof, covenants and agrees to
perform its obligations under such Purchase Contracts, consents to the
provisions of the Principal Agreements, irrevocably authorizes the Purchase
Contract Agent to enter into the Pledge Agreement on its behalf as its
attorney-in-fact, and consents to and agrees to be bound by the Pledge of the
Pledged Securities underlying such Units pursuant to the Pledge Agreement. Each
Holder of Units, by its acceptance thereof, further irrevocably covenants and
agrees that unless such Holder satisfied its obligations to the Company under
the Purchase Contracts underlying such Units as provided in Section 504(a), then
to the extent and in the manner provided in Section 504(b) and the Pledge
Agreement, but subject to the terms thereof, payments in respect of all or a
portion of the principal of or proceeds from the Pledged Securities on the Stock
Purchase Date shall be paid by the Collateral Agent to the Company in
satisfaction of such Holder's obligations under such Purchase Contract and such
Holder shall acquire no right, title or interest in such payments.


                                      -22-
<PAGE>   28


         Upon registration of transfer of a Unit Certificate, the transferee
shall be bound (without the necessity of any other action on the part of such
transferee) by the terms of the Purchase Contracts evidenced thereby and by the
Pledge Agreement and the transferor shall be released from all such obligations
evidenced by the Unit Certificate so transferred. The Company covenants and
agrees, and each Holder of a Unit Certificate, by its acceptance thereof,
likewise covenants and agrees, to be bound by the provisions of this paragraph.

Section 502.  Contract Fees.

         Subject to Section 503, the Company shall pay, on each Quarterly
Payment Date, the Contract Fees payable in respect of each Purchase Contract to
the Person in whose name the Unit Certificate (or one or more Predecessor Unit
Certificates) evidencing such Purchase Contract is registered at the close of
business on the Record Date next preceding such Quarterly Payment Date. The
Contract Fees will be payable at the office of the Purchase Contract Agent in
The City of New York maintained for that purpose or, at the option of the
Company, by check mailed to the address of the Person entitled thereto at such
address as it appears on the Unit Register.

         Upon the occurrence of a Termination Event, the Company's obligation to
pay Contract Fees (including any accrued or deferred Contract Fees) shall cease.

         Each Unit Certificate delivered under this Agreement upon registration
of transfer of, in exchange for or in lieu of any other Unit Certificate shall
carry the rights to receive accrued and unpaid Contract Fees that were carried
by the Purchase Contracts evidenced by such other Unit Certificate.

         Subject to Sections 511 and 512, in the case of any Unit with respect
to which Early Settlement of the underlying Purchase Contract is effected on an
Early Settlement Date after any Record Date and on or prior to the next
succeeding Quarterly Payment Date, Contract Fees, if any, otherwise payable on
such Quarterly Payment Date shall be payable on such Quarterly Payment Date
notwithstanding such Early Settlement, and such Contract Fees shall be paid to
the Person in whose name the Unit Certificate evidencing such Unit (or one or
more Predecessor Unit Certificates) is registered at the close of business on
such Record Date. Except as otherwise expressly provided in the immediately
preceding sentence, the Company shall not be obligated to pay Contract Fees from
and after the Early Settlement Date in respect of any Unit as to which an Early
Settlement has been effected.

         The Company's obligations with respect to Contract Fees are
subordinated and junior in right of payment to the Company's obligations under
any Senior Indebtedness.

Section 503.  Deferral of Payment Dates for Contract Fees.


                                      -23-
<PAGE>   29


         The Company shall have the right, at any time prior to the Stock
Purchase Date, to defer the payment of any or all of the Contract Fees otherwise
payable on any Quarterly Payment Date, but only if the Company shall give the
Holders and the Purchase Contract Agent written notice of its election to defer
such payment (specifying the amount to be deferred) at least ten Business Days
prior to the earlier of (i) the next succeeding Quarterly Payment Date or (ii)
the date the Company is required to give notice of the Record Date or Quarterly
Payment Date with respect to payment of such Contract Fees to NASDAQ or other
applicable self-regulatory organization or to Holders of the Securities, but in
any event not less than one Business Day prior to such date. Any Contract Fees
so deferred shall bear additional Contract Fees thereon at the rate of _____%
annum (computed on the basis of a 360-day year of twelve 30-day months),
compounding on each succeeding Quarterly Payment Date, until paid in full.
Contract Fees so deferred (and additional Contract Fees accrued thereon) shall
be due on the next succeeding Quarterly Payment Date except to the extent that
payment is deferred pursuant to this Section. No Contract Fees may be deferred
to a date that is after the Final Settlement Date or, with respect to any
particular Purchase Contract, Early Settlement thereof. If the Purchase
Contracts are terminated upon the occurrence of a Termination Event, the
Holder's right to receive Contract Fees or deferred Contract Fees (and
additional Contract Fees accrued thereon) will terminate.

Section 504.  Payment of Purchase Price.

         The purchase price for the Shares purchased pursuant to a Purchase
Contract shall be paid by application of payments received by the Company on the
Stock Purchase Date from the Collateral Agent pursuant to the Pledge Agreement
in respect of the principal of the Pledged Securities to secure the obligations
of the relevant Holder under such Purchase Contract. Such application shall
satisfy in full the obligations under such Purchase Contract of the Holder of
the Security of which such Purchase Contract is a part. The Company shall not be
obligated to issue any Shares in respect of a Purchase Contract or deliver any
certificates therefor to the Holder of the related Unit unless the Company shall
have received payment in full of the aggregate purchase price for Shares to be
purchased thereunder in the manner herein set forth.

Section 505.  Issuance of the Shares.

         As promptly as practicable on or after the Stock Purchase Date, upon
receipt by the Company of payment in full of the aggregate purchase price for
the Shares purchased by the Holders pursuant to the foregoing provisions of this
Article, and subject to Section 506(b), the Company shall deposit with the
Purchase Contract Agent, for the benefit of the Holders of the Units, one or
more certificates representing the Shares registered in the name of the Purchase
Contract Agent (or its nominee) as custodian for the Holders (such certificates
for the Shares, together with any dividends or distributions with respect
thereto, being hereinafter referred to as the "Purchase Contract Settlement
Fund") to which the Holders are entitled hereunder. Subject to the foregoing,
upon surrender of a Unit Certificate to the



                                      -24-
<PAGE>   30


Purchase Contract Agent on or after the Stock Purchase Date, with the form of
Settlement Instructions thereon duly completed and executed, the Holder of such
Unit Certificate shall be entitled to receive in exchange therefor a certificate
representing that number of whole Shares which such Holder is entitled to
receive pursuant to the provisions of this Article Five (after taking into
account all Units then held by such Holder) together with cash in lieu of
fractional shares as provided in Section 508 and any dividends or distributions
with respect to such shares constituting part of the Purchase Contract
Settlement Fund, but without any interest thereon, and the Unit Certificate so
surrendered shall forthwith be cancelled. Such shares shall be registered in the
name of the Holder or the Holder's designee as specified in the form of
Settlement Instructions appearing on the surrendered Unit Certificate.

         If any Shares issued in respect of a Purchase Contract are to be
registered to a Person other than the Person in whose name the Unit Certificate
evidencing such Purchase Contract is registered, no such registration shall be
made unless the Person requesting such registration has paid any transfer and
other taxes required by reason of such registration in a name other than that of
the registered Holder of the Unit Certificate evidencing such Purchase Contract
or has established to the satisfaction of the Company that such tax either has
been paid or is not payable.

[Section 506.  Adjustment of Settlement Rate.]

         [(a)     Adjustments for Dividends, Distributions, Stock Splits, Etc.]

         [(1)     In case the Company shall pay or make a dividend or other
distribution on any class of common stock of the Company in Shares, the
Settlement Rate in effect at the opening of business on the day following the
date fixed for the determination of stockholders entitled to receive such
dividend or other distribution shall be increased by dividing such Settlement
Rate by a fraction of which the numerator shall be the number of Shares
outstanding at the close of business on the date fixed for such determination
and the denominator shall be the sum of such number of shares and the total
number of shares constituting such dividend or other distribution, such increase
to become effective immediately after the opening of business on the day
following the date fixed for such determination. For the purposes of this
paragraph (1), the number of Shares at any time outstanding shall not include
shares held in the treasury of the Company but shall include shares issuable in
respect of scrip certificates issued in lieu of fractions of Shares. The Company
will not pay any dividend or make any distribution on the Shares held in the
treasury of the Company.]

         [(2)     In case the Company shall issue rights, options or warrants to
all holders of its Shares (not being available on an equivalent basis to Holders
of the Units upon settlement of the Purchase Contracts underlying such Units)
entitling them, for a period expiring within 45 days after the record date for
the determination of stockholders entitled to receive such rights, options or
warrants, to subscribe for or purchase Shares at a price per share less than


                                      -25-
<PAGE>   31


the Current Market Price per Share on the date fixed for the determination of
stockholders entitled to receive such rights, options or warrants (other than
pursuant to a dividend reinvestment plan), the Settlement Rate in effect at the
opening of business on the day following the date fixed for such determination
shall be increased by dividing such Settlement Rate by a fraction of which the
numerator shall be the number of Shares outstanding at the close of business on
the date fixed for such determination plus the number of Shares which the
aggregate of the offering price of the total number of Shares so offered for
subscription or purchase would purchase at such Current Market Price and the
denominator shall be the number of Shares outstanding at the close of business
on the date fixed for such determination plus the number of Shares so offered
for subscription or purchase, such increase to become effective immediately
after the opening of business on the day following the date fixed for such
determination. For the purposes of this paragraph (2), the number of Shares at
any time outstanding shall not include shares held in the treasury of the
Company but shall include shares issuable in respect of scrip certificates
issued in lieu of fractions of Shares. The Company shall not issue any such
rights, options or warrants in respect of Shares held in the treasury of the
Company.]

         [(3)     In case outstanding Shares shall be subdivided into a greater
number of Shares, the Settlement Rate in effect at the opening of business on
the day following the day upon which such subdivision becomes effective shall be
proportionately increased, and, conversely, in case outstanding Shares shall
each be combined into a smaller number of Shares, the Settlement Rate in effect
at the opening of business on the day following the day upon which such
combination becomes effective shall be proportionately reduced, such increase or
reduction, as the case may be, to become effective immediately after the opening
of business on the day following the day upon which such subdivision or
combination becomes effective.]

         [(4)     In case the Company shall, by dividend or otherwise,
distribute to all holders of its Share evidences of its indebtedness or assets
(including securities, but excluding any rights or warrants referred to in
paragraph (2) of this Section, any dividend or distribution paid exclusively in
cash and any dividend or distribution referred to in paragraph (1) of this
Section), the Settlement Rate shall be increased so that the same shall equal
the rate determined by dividing the Settlement Rate in effect immediately prior
to the close of business on the date fixed for the determination of stockholders
entitled to receive such distribution by a fraction of which the numerator shall
be the Current Market Price per share of the Shares on the date fixed for such
determination less the then fair market value (as determined by the Board of
Directors, whose determination shall be conclusive and described in a Board
Resolution filed with the Purchase Contract Agent) of the portion of the assets
or evidences of indebtedness so distributed applicable to one Share and the
denominator shall be such Current Market Price per Common Share, such adjustment
to become effective immediately prior to the opening of business on the day
following the date fixed for the determination of stockholders entitled to
receive such distribution. In any case in which this paragraph (4) is
applicable, paragraph (2) of this Section shall not be applicable.]




                                      -26-
<PAGE>   32



         [(5)     In case the Company shall, by dividend or otherwise,
distribute to all holders of its Shares cash (excluding any cash that is
distributed in a Reorganization Event to which Section 506(b) applies or as part
of a distribution referred to in paragraph (4) of this Section) in an aggregate
amount that, when combined with (I) the aggregate amount of any other
distributions to all holders of its Shares made exclusively in cash within the
12 months preceding the date of payment of such distribution to the extent such
amount has not already been applied in a prior adjustment pursuant to this
paragraph (5) and (II) the aggregate of the cash plus the fair market value (as
determined by the Board of Directors, whose determination shall be conclusive
and described in a Board Resolution), as of the date of expiration of such
tender or exchange offer, of the consideration paid in respect of any tender or
exchange offer by the Company or any of its subsidiaries for all or any portion
of the Common Stock expiring within the 12 months preceding the date of payment
of such distribution and in respect of which no adjustment pursuant to paragraph
(6) of this Section has been made, exceeds __% of the product of the Current
Market Price per Share on the date fixed for the determination of stockholders
entitled to receive such distribution times the number of Shares outstanding on
such date (such excess portion of such distribution being herein referred to as
the "Excess Amount"), the Settlement Rate shall be increased so that the same
shall equal the rate determined by dividing the Settlement Rate in effect
immediately prior to the close of business on the date fixed for the
determination of stockholders entitled to receive such distribution by a
fraction of which (i) the numerator shall be the Current Market Price per Share
on the date fixed for such determination less an amount equal to (x) such Excess
Amount divided by (y) the number of Shares outstanding at the close of business
on the date fixed for such determination and (ii) the denominator shall be the
Current Market Price per Share on the date fixed for such determination, such
adjustment to become effective immediately prior to the opening of business on
the day following the date fixed for the determination of stockholders entitled
to receive such distribution.]

         [(6)     In case the Company or any subsidiary of the Company shall
consummate a tender or exchange offer for all or any portion of the Shares
(other than normal course issuer bids in accordance with applicable laws) and
pay an aggregate consideration in respect thereof having a fair market value (as
determined by the Board of Directors, whose determination shall be conclusive
and described in a Board Resolution) that, when combined with (I) the aggregate
of the cash plus the fair market value (as determined by the Board of Directors,
whose determination shall be conclusive and described in a Board Resolution), as
of the date of expiration of such tender or exchange offer, of the consideration
paid in respect of any other tender or exchange offer by the Company or any of
its subsidiaries for all or any portion of the Shares expiring within the 12
months preceding the date of expiration of such tender or exchange offer and in
respect of which no adjustment pursuant to this paragraph (6) has been made and
(II) the aggregate amount of any distributions to all holders of the Company's
Shares made exclusively in cash within 12 months preceding the date of
expiration of such tender or exchange offer to the extent such amount has not
already been applied in a prior adjustment pursuant to paragraph (5) of this
Section, exceeds __% of the


                                      -27-
<PAGE>   33


product of the Current Market Price per share of the Common Stock on the date of
expiration of such tender or exchange offer times the number of Shares
outstanding (including any tendered shares) at the close of business on the date
of such expiration, the Settlement Rate shall be increased so that the same
shall equal the rate determined by dividing the Settlement Rate in effect
immediately prior to the close of business on the date of such expiration by a
fraction of which (i) the numerator shall be (A) the product of (I) the Current
Market Price per Share on the date of such expiration and (II) the number of
Shares outstanding (including any tendered shares) at the close of business on
the date of such expiration less (B) the amount of cash plus the fair market
value (determined as aforesaid) of the aggregate consideration paid in respect
of such tender or exchange offer and (ii) the denominator shall be the product
of (A) the Current Market Price per share of the Common Stock on the date of
such expiration and (B) the number of Shares outstanding (including any tendered
shares) at the close of business on the date of such expiration less the number
of shares acquired pursuant to such tender or exchange, such adjustment to
become effective immediately prior to the opening of business on the day
following the date of such expiration.]

         [(7)     The reclassification of Shares into securities including
securities other than Shares (other than any reclassification upon a
Reorganization Event to which Section 506(b) applies) shall be deemed to involve
(i) a distribution of such securities other than Shares to all holders of Shares
(and the effective date of such reclassification shall be deemed to be "the date
fixed for the determination of stockholders entitled to receive such
distribution" and the "date fixed for such determination" within the meaning of
paragraph (4) of this Section), and (ii) a subdivision or combination, as the
case may be, of the number of Shares outstanding immediately prior to such
reclassification into the number of Shares outstanding immediately thereafter
(and the effective date of such reclassification shall be deemed to be "the day
upon which such subdivision becomes effective" or "the day upon which such
combination becomes effective", as the case may be, and "the day upon which such
subdivision or combination becomes effective" within the meaning of paragraph
(3) of this Section).]

         [(8)     The "Current Market Price" per Share on any day means the
average of the daily Closing Prices for the 5 consecutive Trading Days selected
by the Company commencing not more than 20 Trading Days before, and ending not
later than, the earlier of the day in question and the day before the "ex" date
with respect to the issuance or distribution requiring such computation. For
purposes of this paragraph, the term " 'ex' date", when used with respect to any
issuance or distribution, shall mean the first date on which the Shares trade
regular way on such exchange or in such market without the right to receive such
issuance or distribution.]

         [(9)     All adjustments to the Settlement Rate shall be calculated to
the nearest 1/10,000th of a Share (or, if there is not a nearest 1/10,000th of a
share, to the next lower 1/10,000th of a share). No adjustment in the Settlement
Rate shall be required unless such adjustment would require an increase or
decrease of at least one percent therein; provided,


                                      -28-
<PAGE>   34


however, that any adjustments which by reason of this subparagraph are not
required to be made shall be carried forward and taken into account in any
subsequent adjustment. If an adjustment is made to the Settlement Rate pursuant
to paragraph (1), (2), (3), (4), (5), (6), (7) or (10) of this Section 506(a),
an adjustment shall also be made to the Average Trading Price solely to
determine which of clauses (a), (b) or (c) of the definition of Settlement Rate
in Section 501 will apply on the Stock Purchase Date. Such adjustment shall be
made by multiplying the Average Trading Price by a fraction of which the
numerator shall be the Settlement Rate immediately after such adjustment
pursuant to paragraph (1), (2), (3), (4), (5), (6), (7) or (10) of this Section
506(a) and the denominator shall be the Settlement Rate immediately before such
adjustment.]

         [(10)    The Company may make such increases in the Settlement Rate, in
addition to those required by this Section, as it considers to be advisable in
order to avoid or diminish any income tax to any holders of Shares resulting
from any dividend or distribution of stock or issuance of rights or warrants to
purchase or subscribe for stock or from any event treated as such for income tax
purposes or for any other reasons.]

         [(b)     Adjustment for Consolidation, Merger or Other Reorganization
Event. In the event of (i) any consolidation or merger of the Company with or
into another Person (other than a merger or consolidation in which the Company
is the continuing corporation and in which the Shares outstanding immediately
prior to the merger or consolidation is not exchanged for cash, securities or
other property of the Company or another corporation), (ii) any sale, transfer,
lease or conveyance to another Person of the property of the Company as an
entirety or substantially as an entirety, (iii) any statutory exchange of
securities of the Company with another Person (other than in connection with a
merger or acquisition) or (iv) any liquidation, dissolution or winding up of the
Company (any such event, a "Reorganization Event"), each Holder of Units will
thereafter be entitled to receive on the Stock Purchase Date with respect to
each Purchase Contract forming a part thereof, the kind and amount of
securities, cash and other property receivable upon such Reorganization Event by
a Holder of the number of Shares issuable on account of such Purchase Contract
if the Stock Purchase Date had occurred immediately prior to such Reorganization
Event, assuming such Holder of Shares is not a Person with which the Company
consolidated or into which the Company merged or which merged into the Company
or to which such sale or transfer was made, as the case may be ("constituent
Person"), or an Affiliate of a constituent Person, and failed to exercise its
rights of election, if any, as to the kind or amount of securities, cash and
other property receivable upon such Reorganization Event (provided that if the
kind or amount of securities, cash and other property receivable upon such
Reorganization Event is not the same for each Share held immediately prior to
such Reorganization Event by other than a constituent Person or an Affiliate
thereof and in respect of which such rights of election shall not have been
exercised ("non-electing share"), then for the purpose of this Section the kind
and amount of securities, cash and other property receivable upon such
Reorganization Event by each non-electing share shall be deemed to be the kind
and amount so receivable per share by a plurality of the non-electing shares).
In


                                      -29-
<PAGE>   35


the event of such a Reorganization Event, the Person formed by such
consolidation, merger or exchange or the Person which acquires the assets of the
Company or, in the event of a liquidation or dissolution of the Company, the
Company or a liquidating trust created in connection therewith, shall execute
and deliver to the Purchase Contract Agent an agreement supplemental hereto
providing that the Holders of Outstanding Units shall have the rights provided
by this Section 506. Such supplemental agreement shall provide for adjustments
which, for events subsequent to the effective date of such supplemental
agreement, shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Section. The above provisions of this Section
shall similarly apply to successive Reorganization Events.]

[Section 507.  Notice of Adjustments and Certain Other Events.

         (a)      Whenever the Settlement Rate is adjusted as herein provided,
the Company shall:

                  (i)      forthwith compute the adjusted Settlement Rate in
         accordance with Section 506 and prepare and transmit to the Purchase
         Contract Agent an Officers' Certificate setting forth the Settlement
         Rate, the method of calculation thereof in reasonable detail, and the
         facts requiring such adjustment and upon which such adjustment is
         based; and

                  (ii)     within 10 Business Days following the occurrence of
         an event that permits or requires an adjustment to the Settlement Rate
         pursuant to Section 506 (or if the Company is not aware of such
         occurrence, as soon as practicable after becoming so aware), provide a
         written notice to the Holders of the Units of the occurrence of such
         event and a statement in reasonable detail setting forth the method by
         which the adjustment to the Settlement Rate was determined and setting
         forth the adjusted Settlement Rate.

         (b)      The Purchase Contract Agent shall not at any time be under any
duty or responsibility to any holder of Units to determine whether any facts
exist which may require any adjustment of the Settlement Rate, or with respect
to the nature or extent or calculation of any such adjustment when made, or with
respect to the method employed in making the same. The Purchase Contract Agent
shall not be accountable with respect to the validity or value (or the kind or
amount) of any Shares, or of any securities or property, which may at the time
be issued or delivered with respect to any Purchase Contract; and the Purchase
Contract Agent makes no representation with respect thereto. The Purchase
Contract Agent shall not be responsible for any failure of the Company to issue,
transfer or deliver any Shares pursuant to a Purchase Contract or to comply with
any of the duties, responsibilities or covenants of the Company contained in
this Article.]

Section 508.  No Fractional Shares.


                                      -30-
<PAGE>   36

         No fractional shares or scrip representing fractional Shares shall be
issued or delivered upon settlement on the Stock Purchase Date. If Unit
Certificates evidencing more than one Purchase Contract shall be surrendered for
settlement at one time by the same Holder, the number of full Shares which shall
be delivered upon settlement shall be computed on the basis of the aggregate
number of Purchase Contracts evidenced by the Unit Certificates so surrendered.
Instead of any fractional Share which would otherwise be deliverable upon
settlement of any Purchase Contracts on the Stock Purchase Date, the Company,
through the Purchase Contract Agent, shall make a cash payment in respect of
such fractional interest in an amount equal to such fraction times the Average
Trading Price. The Company shall provide the Purchase Contract Agent from time
to time with sufficient funds to permit the Purchase Contract Agent to make all
cash payments required by this Section 508 in a timely manner.

Section 509.  Charges and Taxes.

         The Company will pay all stock transfer and similar taxes attributable
to the initial issuance and delivery of the Shares pursuant to the Purchase
Contracts; provided, however, that the Company shall not be required to pay any
such tax or taxes which may be payable in respect of any exchange of or
substitution for a Unit Certificate evidencing a Purchase Contract or any
issuance of a Share in a name other than that of the registered Holder of a Unit
Certificate surrendered in respect of the Purchase Contracts evidenced thereby,
other than in the name of the Purchase Contract Agent, as custodian for such
Holder, and the Company shall not be required to issue or deliver such share
certificates or Unit Certificates unless or until the Person or Persons
requesting the transfer or issuance thereof shall have paid to the Company the
amount of such tax or shall have established to the satisfaction of the Company
that such tax has been paid.

Section 510.  Termination Event; Notice.

         The Purchase Contracts and the obligations and rights of the Company
and the Holders thereunder, including, without limitation, all obligations and
rights to pay or receive any accrued or deferred Contract Fees or to settle such
Purchase Contracts pursuant to this Article Five, shall immediately and
automatically terminate, without the necessity of any notice or action by any
Holder, the Purchase Contract Agent or the Company, if, on or prior to the Stock
Purchase Date, a Termination Event shall have occurred. Upon the occurrence of a
Termination Event, the Company shall give written notice to the Purchase
Contract Agent, the Collateral Agent and to the Holders at their addresses as
they appear in the Unit Registers. Upon and after the occurrence of a
Termination Event, the provisions of this Article Five (other than this Section
510) shall automatically terminate and be of no further force or effect, and the
Unit Certificates shall thereafter represent only the right to receive the
Pledged Securities forming a part of the Units theretofore evidenced thereby in
accordance with the provisions of Section 402 and the Pledge Agreement.


                                      -31-
<PAGE>   37

[Section 511.  Early Settlement.]

         [(a)     Subject to and upon compliance with the provisions of this
Section 511, at the option of the Holder thereof, Purchase Contracts underlying
Units may be settled early ("Early Settlement") on or prior to _______ on the
_______ Business Day immediately preceding ______ __, ____, as provided herein.
In order to exercise the right to effect Early Settlement with respect to any
Purchase Contracts, the Holder of a Unit Certificate shall deliver such Unit
Certificate to the Purchase Contract Agent at the Corporate Trust Office duly
endorsed for transfer to the Company or in blank with the form of Election to
Settle Early on the reverse side thereof duly completed and accompanied by
payment (which payment shall be made in lawful money of the United States by
certified or cashier's check payable to the order of the Company in immediately
available funds) in an amount ( the "Early Settlement Amount") equal to (i) the
product of (A) the Stated Amount per Unit times (B) the number of Purchase
Contracts with  respect to which the Holder has elected to effect Early
Settlement minus (ii) the aggregate amount of Contract Fees, if any, otherwise
payable on or prior to the immediately preceding Quarterly Payment Date deferred
at the option of the Company pursuant to the Purchase Contract Agreement and
remaining unpaid as of such immediately preceding Quarterly Payment Date plus
(iii) if such delivery is made with respect to any Purchase Contracts during the
period from the close of business on any Record Date next preceding any
Quarterly Payment Date to the opening of business on such Quarterly Payment
Date, an amount equal to the sum of (x) the Contract Fees payable on such
Quarterly Payment Date with respect to such Purchase Contracts plus (y) the
interest with respect to the related Underlying Securities payable on such
Quarterly Payment Date. If the foregoing requirements are first satisfied with
respect to Purchase Contracts underlying Units at or prior to _______ New York
City time, on a Business Day, such date shall be the "Early Settlement Date"
with respect to such Units and if such requirements are first satisfied after
_________, New York City time, on a Business Day or on a day that is not a
Business Day, the "Early Settlement Date" with respect to such Units shall be
the next succeeding Business Day.]

         [(b)     Upon Early Settlement of Purchase Contracts by a Holder of the
related Units, the Company shall issue, and the Holder shall be entitled to
receive regardless of the market price of the Shares on the Early Settlement
Date, ________ Shares on account of each Purchase Contract as to which Early
Settlement is effected (the "Early Settlement Rate"). The Early Settlement Rate
shall be adjusted in the manner and at the same time as the Settlement Rate is
adjusted.]

         [(c)     No later than the ______ Business Day after the applicable
Early Settlement Date the Company shall cause (i) the Shares issuable upon Early
Settlement of Purchase Contracts to be issued and delivered, together with
payment in lieu of any fraction of a share, as provided in Section 508, and (ii)
the related Notes to be released from the Pledge by the Collateral Agent and
transferred, in each case, in book-entry form through the facilities of the
Depository Trust Company to the Purchase Contract Agent for delivery to the
Holder thereof or its designee.]

         [(d)     Upon Early Settlement of any Purchase Contracts, and subject
to receipt of Shares from the Company and the Notes from the Collateral Agent,
as applicable, the Purchase Contract Agent shall, in accordance with the
instructions provided by the Holder thereof on the applicable form of Election
to Settle Early on the reverse of the Unit Certificate evidencing the related
Units, (i) transfer to the Holder the Notes forming a part of such Units in
book-entry form through the facilities of the Depository Trust Company, and


                                      -32-
<PAGE>   38


(ii) deliver to the Holder a certificate or certificates for the full number of
Shares issuable upon such Early Settlement, together with payment in lieu of any
fraction of a share, as provided in Section 508.]

         [(e)     In the event that Early Settlement is effected (i) no Contract
Fees will accrue following the Early Settlement Date, and (ii) with respect to
Purchase Contracts underlying less than all the Units evidenced by a Unit
Certificate, upon such Early Settlement the Company shall execute and the
Purchase Contract Agent shall authenticate, execute on behalf of the Holder and
deliver to the Holder thereof, at the expense of the Company, a Unit Certificate
evidencing the Units as to which Early Settlement was not effected.]

[Section 512.  Early Settlement Upon Merger.]

         [(a)     In the event of a merger or consolidation of the Company of
the type described in clause (i) of Section 506(b) in which the Shares
outstanding immediately prior to such merger or consolidation are exchanged for
consideration consisting of at least 30% cash or cash equivalents (any such
event a "Cash Merger"), then the Company (or the successor to the Company
hereunder) shall be required to offer the Holder of each Unit the right to
settle the Purchase Contract underlying such Unit prior to the Stock Purchase
Date ("Merger Early Settlement") as provided herein. On or before the fifth
Business Day after the consummation of a Cash Merger the Company or, at the
request and expense of the Company, the Purchase Contract Agent shall give all
Holders notice, in the manner provided in Section 105, of the occurrence of the
Cash Merger and of the right of Merger Early Settlement arising as a result
thereof. The Company shall also deliver a copy of such notice to the Purchase
Contract Agent and the Collateral Agent.]

         [Each such notice shall contain:

                  (i) the date, which shall be not less than 20 nor more than 30
         days after the date of such notice, on which the Merger Early
         Settlement will be effected (the "Merger Early Settlement Date");

                  (ii) the date, which shall be three Business Days prior to the
         Merger Early Settlement Date, by which the Merger Early Settlement
         right must be exercised;

                  (iii) the Settlement Rate in effect as a result of such Cash
         Merger and the kind and amount of securities, cash and other property
         receivable by the Holder upon settlement of each Purchase Contract
         pursuant to Section 506(b);

                  (iv) a statement to the effect that all or a portion of the
         Stated Amount payable by the Holder to settle the Purchase Contract
         will be offset against the amount of cash so receivable upon exercise
         of Merger Early Settlement, as applicable;


                                      -33-
<PAGE>   39

                  (v) the instructions a Holder must follow to exercise the
         Merger Early Settlement right; and

                  (vi) a statement to the effect that accrued and unpaid
         Contract Fees in respect of the Purchase Contracts for which Merger
         Early Settlement shall have been effected shall be payable on the
         Merger Early Settlement Date and that upon such payment Contract Fees
         on such Purchase Contracts shall cease to accrue.]

         [(b)     To exercise a Merger Early Settlement right, a Holder shall
deliver to the Purchase Contract Agent on or before _______, New York City time
on the date specified in the notice the Unit Certificate(s) with respect to
which the Merger Early Settlement right is being exercised with the form of
"Election to Settle Early" on the reverse thereof, duly completed accompanied by
payment of the purchase price for the property to be purchased pursuant to the
Purchase Contracts underlying such Units, which payment shall be made in lawful
money of the United States by certified or cashier's check payable to the order
of the Company in immediately available funds in an amount equal to the
Early Settlement Amount.]

         [(c)     In the event a Merger Early Settlement right shall be
exercised by a Holder in accordance with the terms hereof, (i) on the Merger
Early Settlement Date the Company shall deliver or cause to be delivered by the
Purchase Contract Agent to each such exercising Holder the net cash, securities
and other property to be received, as provided herein, by such exercising Holder
in respect of the number of Purchase Contracts for which such Merger Early
Settlement right was exercised in accordance with the settlement instructions
provided by such Holder and (ii) all references herein to Stock Purchase Date
shall be deemed to refer to such Merger Early Settlement Date and all references
to the form of Settlement Instruction shall be deemed to refer to the form of
Election to Settle Early, as applicable.]

         [(d)     In the event that Merger Early Settlement is effected with
respect to less than all of the Purchase Contracts underlying the Units
evidenced by a Unit Certificate, upon such Merger Early Settlement the Company
shall execute and the Purchase Contract Agent shall authenticate, execute on
behalf of the Holders and deliver to the Holder thereof, at the expense of the
Company, a Unit Certificate evidencing the Units as to which Merger Early
Settlement was not effected.]




                                      -34-
<PAGE>   40



                                   ARTICLE SIX

                                    REMEDIES

Section 601. Unconditional Rights of Holders.

         Notwithstanding any other provision in this Agreement, the Holder of
any Unit shall have the right, which is absolute and unconditional but which is
subject to Section 510, to purchase Shares pursuant to the Purchase Contract
underlying such Unit and, in each such case, to institute suit for the
enforcement of any such right, and such rights shall not be impaired without the
consent of such Holder.

Section 602.  Restoration of Rights and Remedies.

         If any Holder of Units has instituted any proceeding to enforce any
right or remedy under this Agreement and such proceeding has been discontinued
or abandoned for any reason, or has been determined adversely to such Holder,
then and in every such case, subject to any determination in such proceeding,
the Company and such Holder shall be restored severally and respectively to
their former positions hereunder and thereafter all rights and remedies of such
Holder shall continue as though no such proceeding had been instituted.

Section 603.  Rights and Remedies Cumulative.

         Except as otherwise provided with respect to the replacement of
mutilated, destroyed, lost or stolen Unit Certificates in the last paragraph of
Section 306, no right or remedy herein conferred upon or reserved to the Holders
of Units is intended to be exclusive of any other right or remedy, and every
right and remedy shall, to the extent permitted by law, be cumulative and in
addition to every other right and remedy given hereunder or now or hereafter
existing at law or in equity or otherwise. The assertion or employment of any
right or remedy hereunder, or otherwise, shall not prevent the concurrent
assertion or employment of any other appropriate right or remedy.

Section 604.  Delay or Omission Not Waiver.

         No delay or omission of any Holder to exercise any right or remedy
shall impair any such right or remedy or constitute a waiver of any such right.
Every right and remedy given by this Article or by law to the Holders may be
exercised from time to time, and as often as may be deemed expedient, by such
Holders.

Section 605.  Undertaking for Costs.

         All parties to this Agreement agree, and each Holder of any Unit by its
acceptance of the Unit Certificate evidencing such Unit shall be deemed to have
agreed, that any court


                                      -35-
<PAGE>   41

may in its discretion require, in any suit for the enforcement of any right or
remedy under this Agreement, or in any suit against the Purchase Contract Agent
for any action taken, suffered or omitted by it as Purchase Contract Agent, the
filing by any party litigant in such suit of an undertaking to pay the costs of
such suit, and that such court may in its discretion assess reasonable costs,
including reasonable attorneys' fees, against any party litigant in such suit,
having due regard to the merits and good faith of the claims or defenses made by
such party litigant; provided that the provisions of this Section shall not
apply to any suit instituted by the Company, to any suit instituted by the
Purchase Contract Agent, to any suit instituted by any Holder of Units, or group
of Holders, holding in the aggregate more than 10% of the number of Outstanding
Units, or to any suit instituted by any Holder of Units for the enforcement of
payments due in respect of Pledged Securities or Contract Fees on Purchase
Contracts underlying such Units on or after the respective due dates therefor,
or for enforcement of the right to purchase Shares under the Purchase Contracts
constituting a part of such Units.

Section 606.  Waiver of Stay or Extension Laws.

         The Company covenants (to the extent that it may lawfully do so) that
it will not at any time insist upon, or plead, or in any manner whatsoever claim
or take the benefit or advantage of, any stay or extension law wherever enacted,
now or at any time hereafter in force, which may affect the covenants or the
performance of this Agreement; and the Company (to the extent that it may
lawfully do so) hereby expressly waives all benefit or advantage of any such law
and covenants that it will not hinder, delay or impede the execution of any
power herein granted to the Purchase Contract Agent or the Holders, but will
suffer and permit the execution of every such power as though no such law had
been enacted.

                                  ARTICLE SEVEN

                           THE PURCHASE CONTRACT AGENT

Section 701.  Certain Duties and Responsibilities.

              (a)(i)    The Purchase Contract Agent undertakes to perform,
          with respect to the Units, such duties and only such duties as are
          specifically set forth in this Agreement, and no implied covenants or
          obligations shall be read into this Agreement against the Purchase
          Contract Agent; and

               (ii)      the Purchase Contract Agent may, with respect to
          the Units, conclusively rely, as to the truth of the statements and
          the correctness of the opinions expressed therein, upon certificates
          or opinions furnished to the Purchase Contract Agent and conforming to
          the requirements of this Agreement, but in the case of any
          certificates or opinions which by any provision hereof are
          specifically required to be


                                      -36-
<PAGE>   42


          furnished to the Purchase Contract Agent, the Purchase Contract Agent
          shall be under a duty to examine the same to determine whether or not
          they conform to the requirements of this Agreement but shall have no
          duty to confirm or investigate the accuracy or mathematical
          calculations or other facts stated therein.

          (b)       Purchase Contract Agent shall not be liable for any action
taken or omitted or for any loss or injury resulting from its actions or its
performance or lack of performance of its duties hereunder in the absence of
gross negligence or willful misconduct on its part;

                    (i)       the Purchase Contract Agent shall not be liable
          for any error of judgment made in good faith by a Responsible Officer,
          unless it shall be proved that the Purchase Contract Agent was grossly
          negligent in ascertaining the pertinent facts;

                    (ii)      no provision of this Agreement shall require the
          Purchase Contract Agent to expend or risk its own funds or otherwise
          incur any financial liability in the performance of any of its duties
          hereunder, or in the exercise of any of its rights or powers, if it
          shall have reasonable grounds for believing that repayment of such
          funds or adequate indemnity against such risk or liability is not
          reasonably assured to it; and

                    (iii)     In no event shall the Purchase Contract Agent be
          liable for any indirect, consequential, punitive or special damages,
          regardless of the form of action and whether or not such damages were
          foreseeable or contemplated.

          (c)       Whether or not therein expressly so provided, every
provision of this Agreement relating to the conduct or affecting the liability
of or affording protection to the Purchase Contract Agent shall be subject to
the provisions of this Section.

Section 702.  Notice of Default.

          Within 90 days after the occurrence of any default by the Company
hereunder, of which a Responsible Officer of the Purchase Contract Agent has
actual knowledge, the Purchase Contract Agent shall transmit by mail to all
Holders of Units, as their names and addresses appear in the Unit Registers,
notice of such default hereunder, unless such default shall have been cured or
waived.

Section 703.  Certain Rights of Purchase Contract Agent.

         Subject to the provisions of Section 701:

                    (a)       the Purchase Contract Agent may conclusively rely
          and shall be protected in acting or refraining from acting upon any
          resolution, certificate, statement, instrument, opinion, report,
          notice, request, direction, consent, order,


                                      -37-
<PAGE>   43



          bond, debenture, note, other evidence of indebtedness or other paper
          or document believed by it to be genuine and to have been signed or
          presented by the proper party or parties;

                    (b)       any request or direction of the Company mentioned
          herein shall be sufficiently evidenced by an Officers' Certificate,
          Issuer Order or Issuer Request, and any resolution of the Board of
          Directors of the Company may be sufficiently evidenced by a Board
          Resolution;

                    (c)       whenever in the administration of this Agreement
          the Purchase Contract Agent shall deem it desirable that a matter be
          proved or established prior to taking, suffering or omitting any
          action hereunder, the Purchase Contract Agent (unless other evidence
          be herein specifically prescribed) may, in the absence of bad faith on
          its part, conclusively rely upon an Officers' Certificate of the
          Company;

                    (d)       the Purchase Contract Agent may consult with
          counsel of its selection and the advice of such counsel or any Opinion
          of Counsel shall be full and complete authorization and protection in
          respect of any action taken, suffered or omitted by it hereunder in
          good faith and in reliance thereon;

                    (e)       the Purchase Contract Agent shall not be bound to
          make any investigation into the facts or matters stated in any
          resolution, certificate, statement, instrument, opinion, report,
          notice, request, direction, consent, order, bond, debenture, note,
          other evidence of indebtedness or other paper or document; and

                    (f)       the Purchase Contract Agent may execute any of its
          powers hereunder or perform any duties hereunder either directly or by
          or through agents or attorneys and the Purchase Contract Agent shall
          not be responsible for any misconduct or negligence on the part of any
          agent or attorney appointed with due care by it hereunder.

Section 704.  Not Responsible for Recitals or Issuance of Units.

          The recitals contained herein and in the Unit Certificates shall be
taken as the statements of the Company and the Purchase Contract Agent assumes
no responsibility for their correctness. The Purchase Contract Agent makes no
representations as to the validity or sufficiency of this Agreement or of the
Units. The Purchase Contract Agent shall not be accountable for the use or
application by the Company of the proceeds in respect of the Notes or Purchase
Contracts.

Section 705.  May Hold Units.

         Any Unit Registrar or any other agent of the Company, or the Purchase
Contract Agent, in its individual or any other capacity, may become the owner or
pledgee of Units and



                                      -38-
<PAGE>   44



may otherwise deal with the Company with the same rights it would have if it
were not Unit Registrar or such other agent, or the Purchase Contract Agent.

Section 706.  Money Held in Trust.

          Money held by the Purchase Contract Agent hereunder need not be
segregated from other funds except to the extent required by law. The Purchase
Contract Agent shall be under no obligation to invest or pay interest on any
money received by it hereunder except as otherwise agreed in writing with the
Company.

Section 707.  Compensation and Reimbursement.

          The Company agrees:

                    (a)       to pay to the Purchase Contract Agent from time to
          time such compensation for all services rendered by it hereunder as
          the Company and the Purchase Contract Agent shall from time to time
          agree in writing;

                    (b)       except as otherwise expressly provided herein, to
          reimburse the Purchase Contract Agent upon its request for all
          reasonable expenses, disbursements and advances incurred or made by
          the Purchase Contract Agent in accordance with any provision of this
          Agreement (including the reasonable compensation and the expenses and
          disbursements of its agents and counsel), except any such expense,
          disbursement or advance as may be attributable to its gross negligence
          or bad faith; and

                    (c)       to indemnify the Purchase Contract Agent and any
          predecessor Purchase Contract Agent and their agents for, and to hold
          each of them harmless against, any and all loss, damage, claim,
          liability or expense, including taxes (other than taxes based upon,
          measured by or determined by the income of the Purchase Contract
          Agent), incurred without gross negligence or bad faith on its part,
          arising out of or in connection with the acceptance or administration
          of its duties hereunder, including the costs and expenses of defending
          itself against any claim or liability in connection with the exercise
          or performance of any of its powers or duties hereunder.

          The provision of this Section 707 shall survive the termination of
this Agreement and the resignation or removal of the Purchase Contract Agent.

Section 708.  Purchase Contract Agent Required; Eligibility.

          There shall at all times be a Purchase Contract Agent hereunder which
shall be a corporation or banking association organized and doing business under
the laws of the United States of America, any State thereof or the District of
Columbia, authorized under


                                      -39-
<PAGE>   45

such laws to exercise corporate trust powers, having a combined capital and
surplus of at least $50,000,000, subject to supervision or examination by
Federal or State authority and having a corporate trust office in the Borough of
Manhattan, The City of New York, if there be such a corporation in the Borough
of Manhattan, The City of New York qualified and eligible under this Article and
willing to act on reasonable terms. If such corporation publishes reports of
condition at least annually, pursuant to law or to the requirements of said
supervising or examining authority, then for the purposes of this Section, the
combined capital and surplus of such corporation shall be deemed to be its
combined capital and surplus as set forth in its most recent report of condition
so published. If at any time the Purchase Contract Agent shall cease to be
eligible in accordance with the provisions of this Section, it shall resign
immediately in the manner and with the effect hereinafter specified in this
Article.

Section 709.  Resignation and Removal; Appointment of Successor.

                  (a)      No resignation or removal of the Purchase Contract
         Agent and no appointment of a successor Purchase Contract Agent
         pursuant to this Article shall become effective until the acceptance of
         appointment by the successor Purchase Contract Agent in accordance with
         the applicable requirements of Section 710.

                  (b)      The Purchase Contract Agent may resign at any time by
         giving written notice thereof to the Company __ days prior to the
         effective date of such resignation. If the instrument of acceptance by
         a successor Purchase Contract Agent required by Section 710 shall not
         have been delivered to the Purchase Contract Agent within __ days after
         the giving of such notice of resignation, the resigning Purchase
         Contract Agent may petition any court of competent jurisdiction for the
         appointment of a successor Purchase Contract Agent.

                  (c)      The Purchase Contract Agent may be removed at any
         time by Act of the Holders of a majority in number of the Outstanding
         Units delivered to the Purchase Contract Agent and the Company.

                  (d)      If at any time

                           (i)      the Purchase Contract Agent fails to comply
                  with Section 310(b) of the TIA, as if the Purchase Contract
                  Agent were an indenture trustee under an indenture qualified
                  under the TIA, after written request therefor by the Company
                  or by any Holder who has been a bona fide Holder of a Unit for
                  at least six months, or

                           (ii)     the Purchase Contract Agent shall cease to
                  be eligible under Section 708 and shall fail to resign after
                  written request therefor by the Company or by any such Holder,
                  or

                                      -40-
<PAGE>   46


                           (iii)    the Purchase Contract Agent shall become
                  incapable of acting or shall be adjudged a bankrupt or
                  insolvent or a receiver of the Purchase Contract Agent or of
                  its property shall be appointed or any public officer shall
                  take charge or control of the Purchase Contract Agent or of
                  its property or affairs for the purpose of rehabilitation,
                  conservation or liquidation,

then, in any such case, (x) the Company by a Board Resolution may remove the
Purchase Contract Agent, or (y) any Holder who has been a bona fide Holder of a
Unit for at least six months may, on behalf of himself and all others similarly
situated, petition any court of competent jurisdiction for the removal of the
Purchase Contract Agent and the appointment of a successor Purchase Contract
Agent.

                  (e)      If the Purchase Contract Agent shall resign, be
removed or become incapable of acting, or if a vacancy shall occur in the office
of Purchase Contract Agent for any cause, the Company, by a Board Resolution,
shall promptly appoint a successor Purchase Contract Agent and shall comply with
the applicable requirements of Section 710. If no successor Purchase Contract
Agent shall have been so appointed by the Company and accepted appointment in
the manner required by Section 710, the Purchase Contract Agent or any Holder
who has been a bona fide Holder of a Unit for at least six months may, on behalf
of himself and all others similarly situated, petition any court of competent
jurisdiction for the appointment of a successor Purchase Contract Agent.

                  (f)      The Company shall give, or shall cause such successor
Purchase Contract Agent to give, notice of each resignation and each removal of
the Purchase Contract Agent and each appointment of a successor Purchase
Contract Agent by mailing written notice of such event by first-class mail,
postage prepaid, to all Holders of Units as their names and addresses appear in
the Unit Registers. Each notice shall include the name of the successor Purchase
Contract Agent and the address of its Corporate Trust Office.

Section 710.  Acceptance of Appointment by Successor.

                  (a)      In case of the appointment hereunder of a successor
Purchase Contract Agent, every such successor Purchase Contract Agent so
appointed shall execute, acknowledge and deliver to the Company and to the
retiring Purchase Contract Agent an instrument accepting such appointment, and
thereupon the resignation or removal of the retiring Purchase Contract Agent
shall become effective and such successor Purchase Contract Agent, without any
further act, deed or conveyance, shall become vested with all the rights,
powers, agencies and duties of the retiring Purchase Contract Agent; but, on the
request of the Company or the successor Purchase Contract Agent, such retiring
Purchase Contract Agent shall, upon payment of its charges, execute and deliver
an instrument transferring to such successor Purchase Contract Agent all the
rights, powers and trusts of the retiring Purchase Contract Agent and shall duly
assign, transfer and deliver to such successor Purchase Contract Agent all
property and money held by such retiring Purchase Contract Agent hereunder.


                                      -41-
<PAGE>   47

                  (b)      Upon request of any such successor Purchase Contract
Agent, the Company shall execute any and all instruments for more fully and
certainly vesting in and confirming to such successor Purchase Contract Agent
all such rights, powers and agencies referred to in paragraph (a) of this
Section.

                  (c)      No successor Purchase Contract Agent shall accept its
appointment unless at the time of such acceptance such successor Purchase
Contract Agent shall be qualified and eligible under this Article.

Section 711.  Merger, Conversion, Consolidation or Succession to Business.

         Any corporation or banking association into which the Purchase Contract
Agent may be merged or converted or with which it may be consolidated, or any
corporation or banking association resulting from any merger, conversion or
consolidation to which the Purchase Contract Agent shall be a party, or any
corporation or banking association succeeding to all or substantially all the
corporate trust business of the Purchase Contract Agent, shall be the successor
of the Purchase Contract Agent hereunder, provided such corporation or banking
association shall be otherwise qualified and eligible under this Article,
without the execution or filing of any paper or any further act on the part of
any of the parties hereto. In case any Unit Certificates shall have been
authenticated and executed on behalf of the Holders, but not delivered, by the
Purchase Contract Agent then in office, any successor by merger, conversion or
consolidation to such Purchase Contract Agent may adopt such authentication and
execution and deliver the Unit Certificates so authenticated and executed with
the same effect as if such successor Purchase Contract Agent had itself
authenticated and executed such Units.

Section 712.  Preservation of Information; Communications to Holders.

         (a)      The Purchase Contract Agent shall preserve, in as current a
form as is reasonably practicable, the names and addresses of Holders received
by the Purchase Contract Agent in its capacity as Unit Registrar.

         (b)      If three or more Holders (herein referred to as "applicants")
apply in writing to the Purchase Contract Agent, and furnish to the Purchase
Contract Agent reasonable proof that each such applicant has owned a Unit for a
period of at least six months preceding the date of such application, and such
application states that the applicants desire to communicate with other Holders
with respect to their rights under this Agreement or under the Units and is
accompanied by a copy of the form of proxy or other communication which such
applicants propose to transmit, then the Purchase Contract Agent shall, within
five Business Days after the receipt of such application, afford such applicants
access to the information preserved at the time by the Purchase Contract Agent
in accordance with Section 712(a).


                                      -42-
<PAGE>   48


         (c)      Every Holder of Units, by receiving and holding the Unit
Certificates evidencing the same, agrees with the Company and the Purchase
Contract Agent that none of the Company, the Purchase Contract Agent nor any
agent of any of them shall be held accountable by reason of the disclosure of
any such information as to the names and addresses of the Holders in accordance
with Section 712(b), regardless of the source from which such information was
derived.

Section 713.  No Obligations of Purchase Contract Agent.

         Except to the extent otherwise provided in this Agreement, the Purchase
Contract Agent assumes no obligations and shall not be subject to any liability
under this Agreement or any Purchase Contract in respect of the obligations of
the Holder of any Unit thereunder. The Company agrees, and each Holder of a Unit
Certificate, by its acceptance thereof, shall be deemed to have agreed, that the
Purchase Contract Agent's execution of the Unit Certificates on behalf of the
Holders shall be solely as agent and attorney-in-fact for the Holders, and that
the Purchase Contract Agent shall have no obligation to perform such Purchase
Contracts on behalf of the Holders, except to the extent expressly provided in
Article Five hereof.

Section 714.  Tax Compliance.

         (a)      The Purchase Contract Agent, on its own behalf and on behalf
of the Company, will comply with all applicable certification, information
reporting and withholding (including "backup" withholding) requirements imposed
by applicable tax laws, regulations or administrative practice with respect to
any payments made with respect to the Units, including Form 1099. Such
compliance shall include, without limitation, the timely payment of all amounts
required to be withheld to the appropriate taxing authority or its designated
agent.

         (b)      The Purchase Contract Agent shall comply with any direction
received from the Company with respect to the application of such requirements
to particular payments or Holders or in other particular circumstances, and may
for purposes of this Agreement rely on any such direction in accordance with the
provisions of Section 701(a)(ii) hereof.

         (c)      The Purchase Contract Agent shall maintain all appropriate
records documenting compliance with such requirements, and shall make such
records available, on written request, to the Company or to its authorized
representative within a reasonable period of time after receipt of such request.



                                      -43-
<PAGE>   49

                                  ARTICLE EIGHT

                             SUPPLEMENTAL AGREEMENTS

Section 801.  Supplemental Agreements Without Consent of Holders.

         Without the consent of any Holders, the parties to either Principal
Agreement, at any time and from time to time, may enter into one or more
agreements supplemental hereto or thereto, in form satisfactory to such parties,
for any of the following purposes:

                  (1)      to evidence the succession of another Person to any
         such party, and the assumption by any such successor of the covenants
         of such party herein or therein and under the Units; 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 Purchase Contract Agent; or

                  (4)      to make provision with respect to the rights of
         Holders pursuant to the requirements of Section 506(b); or

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

Section 802.  Supplemental Agreements 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 parties to either
Principal Agreement, such parties (when authorized, in the case of the Company,
by a Board Resolution) may enter into an agreement or agreements supplemental to
such Principal Agreement for the purpose of modifying in any manner the terms of
the Units, or the provisions of such Principal Agreement or the rights of the
Holders in respect of the Units; provided, however, that no such supplemental
agreement shall, without the consent of the Holder of each Outstanding Unit
affected thereby,

                  (1)      change any payment date;

                  (2)      change the amount or type of Pledged Securities
         required to be pledged to secure obligations under the Units, impair
         the right of the Holder of any Unit to receive distributions or
         interest payments on the underlying Pledged



                                      -44-
<PAGE>   50


         Securities or otherwise adversely affect the Holder's rights in or to
         such Pledged Securities;

                  (3)      impair the right to institute suit for the
         enforcement of any Purchase Contract;

                  (4)      reduce the number of Shares to be purchased pursuant
         to any Purchase Contract, increase the price to purchase Shares upon
         settlement of any Purchase Contract, change the Stock Purchase Date or
         otherwise adversely affect the Holder's rights under any Purchase
         Contract; or

                  (5)      reduce the percentage of the Outstanding Units the
         consent of whose Holders is required for any such supplemental
         agreement.

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

         The Company may, but shall not be obligated to, fix a record date for
the purpose of determining the Persons entitled to consent to any supplemental
agreement to any Principal Agreement. If a record date is fixed, the Holders on
such record date, or their duly designated proxies, and only such Persons, shall
be entitled to consent to such supplemental agreement, whether or not such
Holders remain Holders after such record date; provided, that unless such
consent shall have become effective by virtue of the requisite percentage having
been obtained prior to the date which is 90 days after such record date, any
such consent previously given shall automatically and without further action by
any Holder be cancelled and of no further effect.

Section 803.  Execution of Supplemental Agreements.

         In executing, or accepting the additional agencies created by, any
supplemental agreement permitted by this Article or the modifications thereby of
the agencies created by the Principal Agreements, the Purchase Contract Agent
shall be entitled to receive and (subject to Section 701) shall be fully
protected in relying upon, an Opinion of Counsel stating that the execution of
such supplemental agreement is authorized or permitted by this Agreement. The
Purchase Contract Agent may, but shall not be obligated to, enter into any such
supplemental agreement which affects the Unit Agent's own rights, duties or
immunities under this Agreement or otherwise.


                                      -45-
<PAGE>   51


Section 804.  Effect of Supplemental Agreements.

         Upon the execution of any supplemental agreement under this Article,
the relevant Principal Agreement shall be modified in accordance therewith, and
such supplemental agreement shall form a part of such Principal Agreement for
all purposes; and every Holder of Unit Certificates theretofore or thereafter
authenticated, executed on behalf of the Holder and delivered hereunder shall be
bound thereby.

Section 805.  Reference to Supplemental Agreements.

         Unit Certificates authenticated, executed on behalf of the Holders and
delivered after the execution of any supplemental agreement pursuant to this
Article may, and shall if required by the Purchase Contract Agent, bear a
notation in form approved by the Purchase Contract Agent as to any matter
provided for in such supplemental agreement. If the Company shall so determine,
new Unit Certificates so modified as to conform, in the opinion of the Purchase
Contract Agent and the Company, to any such supplemental agreement may be
prepared and executed by the Company and authenticated, executed on behalf of
the Holders and delivered by the Purchase Contract Agent in exchange for
Outstanding Unit Certificates evidencing the same number of Units.


                                  ARTICLE NINE

                    CONSOLIDATION, MERGER, SALE OR CONVEYANCE

Section 901.  Covenant Not to Merge, Consolidate, Sell or Convey Property
              Except Under Certain Conditions.

         The Company covenants that it will not merge or consolidate with any
other Person or sell, assign, transfer, lease or convey all or substantially all
of its assets to any Person, unless (a) the Company shall be the continuing
corporation, or the successor (if other than the Company) shall be a corporation
organized and existing under the laws of the United States of America or a State
thereof and such corporation shall assume the obligations of the Company under
the Purchase Contracts and the Pledge Agreement by one or more supplemental
agreements in form satisfactory to the Purchase Contract Agent and, in the case
of the Pledge Agreement, the Collateral Agent, executed and delivered to the
Purchase Contract Agent, and, in the case of the Pledge Agreement, the
Collateral Agent by such corporation, and (b) the Company or such successor
corporation, as the case may be, shall not, immediately after such merger or
consolidation, or such sale, assignment, transfer, lease or conveyance, be in
default in the performance of any covenant or condition under any Principal
Agreement or under any of the Units.

Section 902.  Rights and Duties of Successor Corporation.


                                      -46-
<PAGE>   52


         In case of any such consolidation, merger, sale, assignment, transfer,
lease or conveyance and upon any such assumption by the successor corporation,
such successor corporation shall succeed to and be substituted for the Company
with the same effect as if it had been named in the Principal Agreements as the
Company. Such successor corporation thereupon may cause to be signed, and may
issue either in its own name or in the name of XO Communications, Inc., any or
all of the Unit Certificates evidencing Units issuable hereunder which
theretofore shall not have been signed by the Company and delivered to the
Purchase Contract Agent; and, upon the order of such successor corporation,
instead of the Company, and subject to all the terms, conditions and limitations
in this Agreement prescribed, the Purchase Contract Agent shall authenticate and
execute on behalf of the Holders and deliver any Unit Certificates which
previously shall have been signed and delivered by the officers of the Company
to the Purchase Contract Agent for authentication and execution, and any Unit
Certificate evidencing Units which such successor corporation thereafter shall
cause to be signed and delivered to the Purchase Contract Agent for that
purpose. All the Unit Certificates so issued shall in all respects have the same
legal rank and benefit under this Agreement as the Unit Certificates theretofore
or thereafter issued in accordance with the terms of this Agreement as though
all of such Unit Certificates had been issued at the date of the execution
hereof.

         In case of any such consolidation, merger, sale or conveyance such
change in phraseology and form (but not in substance) may be made in the Unit
Certificates evidencing Units thereafter to be issued as may be appropriate.

Section 903.  Opinion of Counsel to Purchase Contract Agent.

         The Purchase Contract Agent, subject to Sections 701 and 703, shall be
provided an Opinion of Counsel as conclusive evidence that any such
consolidation, merger, sale, assignment, transfer, lease or conveyance, and any
such assumption, complies with the provisions of this Article.

                                   ARTICLE TEN

                                    COVENANTS

Section 1001.  Performance Under Purchase Contracts.

         The Company covenants and agrees for the benefit of the Holders from
time to time of the Units that it will duly and punctually perform its
obligations under the Purchase Contracts in accordance with the terms of the
Purchase Contracts and this Agreement.

Section 1002.  Maintenance of Office or Agency.


                                      -47-
<PAGE>   53



         The Company will maintain in the Borough of Manhattan, The City of New
York an office or agency where Unit Certificates may be presented or surrendered
for acquisition of Shares upon settlement and for transfer of Pledged Securities
upon occurrence of a Termination Event, where Unit Certificates may be
surrendered for registration of transfer or exchange, and where notices and
demands to or upon the Company in respect of the Units and this Agreement may be
served. The Company will give prompt written notice to the Purchase Contract
Agent of the location, and any change in the location, of such office or agency.
If at any time the Company shall fail to maintain any such required office or
agency or shall fail to furnish the Purchase Contract Agent with the address
thereof, such presentations, surrenders, notices and demands may be made or
served at the Corporate Trust Office, and the Company hereby appoints the
Purchase Contract Agent as its agent to receive all such presentations,
surrenders, notices and demands.

         The Company may also from time to time designate one or more other
offices or agencies where Unit Certificates may be presented or surrendered for
any or all such purposes and may from time to time rescind such designations;
provided, however, that no such designation or rescission shall in any manner
relieve the Company of its obligation to maintain an office or agency in the
Borough of Manhattan, The City of New York for such purposes. The Company will
give prompt written notice to the Purchase Contract Agent of any such
designation or rescission and of any change in the location of any such other
office or agency. The Company hereby designates as the place of payment for the
Units the Corporate Trust Office and appoints the Purchase Contract Agent at its
Corporate Trust Office as paying agent in such city.

Section 1003.  Company to Reserve Shares.

         The Company shall at all times prior to the Stock Purchase Date reserve
and keep available, free from preemptive rights, out of its authorized but
unissued Shares the full number of Shares issuable against tender of payment in
respect of all Purchase Contracts underlying the Units.

Section 1004.  Covenants as to Shares.

         The Company covenants that all Shares which may be issued against
tender of payment in respect of the Purchase Contracts underlying the Units
will, upon issuance, be newly issued (i.e., not issued out of treasury shares)
and be duly authorized, validly issued, fully paid and nonassessable.

Section 1005.  Statements of Officers of the Company as to Default.

         The Company will deliver to the Purchase Contract Agent, on or before
________ __ in each year (beginning the first _________ __ after the date of the
original issuance of the Units hereunder) a brief certificate from the principal
executive, financial or accounting


                                      -48-
<PAGE>   54



officer of the Company stating that in the course of the performance by the
signer of his or her duties as an officer of the Company he or she would
normally have knowledge of any default or non-compliance by the Company in the
performance of any covenants or conditions contained in this Agreement, stating
whether or not he or she has knowledge of any such default or non-compliance
and, if so, specifying each such default or non-compliance of which the signer
has knowledge and the nature thereof. For purposes of this Section 1005,
non-compliance or default shall be determined without regard to any grace period
or requirement of notice.



                                      -49-
<PAGE>   55



         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:
                                               --------------------------------



                                            --------------------------,
                                            as Purchase Contract Agent



                                            By:
                                               --------------------------------




                                      -50-
<PAGE>   56



                                                                       EXHIBIT A



                            FORM OF UNIT CERTIFICATE

                             XO COMMUNICATIONS, INC.

                             _________________ UNITS

                        (STATED AMOUNT $______ PER UNIT)


CUSIP No. ___________

No. R-____                                                    ____________ Units


                  This Unit Certificate certifies that ______________ is the
registered Holder of the number of Units set forth above. Each Unit represents
the right to purchase Shares under a Purchase Contract with XO Communications,
Inc., a Delaware corporation (the "Company"), together with ownership of the
______________ (the "Notes") or other Pledged Securities pledged to secure the
obligations owed to the Company under such Purchase Contract, subject to the
pledge arrangements securing the foregoing obligations.

                  Each Purchase Contract evidenced hereby is governed by and set
forth in a Purchase Contract Agreement, dated as of _________ __, ____ (the
"Purchase Contract Agreement"), between the Company and _________________, as
Purchase Contract Agent (herein called the "Purchase Contract Agent"). All terms
used herein which are not defined herein and which are defined in the Purchase
Contract Agreement have the meanings set forth therein. The Pledge evidenced
hereby is governed by the Pledge Agreement. Reference is hereby made to the
Purchase Contract Agreement and the Pledge Agreement, and any supplemental
agreements thereto, for a description of the respective rights, limitations of
rights, obligations, duties and immunities thereunder of the Purchase Contract
Agent, the Company, the Collateral Agent and the Holders. The summary contained
herein is qualified in its entirety by the provisions of the Principal
Agreements, and the Principal Agreements shall govern the rights of the parties
to the extent that there is any conflict between such summary and such
provisions.

                  Each Purchase Contract evidenced hereby obligates the Holder
of this Unit Certificate to purchase, and the Company to sell, on _______ __,
____ (the "Stock Purchase Date"), at a price equal to $_____ per unit (the
"Stated Amount"), a number of Shares, having such terms as set forth in the
Company's certificate of incorporation, as amended from time to time, [and
certificate of designation relating to such Shares] ("Shares"), of the Company
equal to the Settlement Rate, unless on or prior to the Stock Purchase Date
there shall have occurred a Termination Event. The "Settlement Rate" is equal to
(a) if the Average Trading Price (as defined in the Purchase Contract Agreement)
is greater than or




                                      A-1
<PAGE>   57




equal to $____ (the "Threshold Appreciation Price"), ________ of a Share per
Purchase Contract, (b) if the Average Trading Price is less than the Threshold
Appreciation Price but is greater than the Stated Amount, a fractional Share per
Purchase Contract equal to the Stated Amount divided by the Average Trading
Price (rounded to the nearest 1/10,000th of a share or, if there is no nearest
1/10,000th of a share, rounded downward to the nearest 1/10,000th of a share)
and (c) if the Average Trading Price is less than or equal to the Stated Amount,
one Share per Purchase Contract, in each case subject to adjustment as provided
in the Purchase Contract Agreement. No fractional Shares will be issued upon
settlement of Purchase Contracts, but instead of issuing any fractional interest
the Company shall make a cash payment as provided in the Purchase Contract
Agreement. The purchase price for the Shares purchased pursuant to each Purchase
Contract shall be paid by application of payments received by the Company on the
Stock Purchase Date from the Collateral Agent pursuant to the Pledge Agreement
in respect of the principal of the Pledged Securities to secure the obligations
of the Holder under such Purchase Contract.  The Company shall not be obligated
to issue any Shares in respect of a Purchase Contract or deliver any
certificates therefor to the Holder unless it shall have received payment in
full of the aggregate purchase price for the Shares to be purchased thereunder
in the manner herein set forth.

                  The Purchase Contracts and the obligations and rights of the
Company and the Holders thereunder shall immediately and automatically
terminate, without the necessity of any notice or action by any Holder, the
Purchase Contract Agent or the Company, if, on or prior to the Stock Purchase
Date, a Termination Event shall have occurred. Upon and after the occurrence of
a Termination Event, the Collateral Agent shall release the Pledged Securities
from the Pledge. The Units shall thereafter represent the right to receive the
Pledged Securities forming a part of such Units in accordance with the
provisions of the Purchase Contract Agreement and the Pledge Agreement.

         The Company shall pay, on each ___________, _____________, __________
and ___________, commencing ________ __, ____ (each, a "Quarterly Payment
Date"), in respect of each Purchase Contract evidenced hereby, a fee (the
"Contract Fee") accruing on the Stated Amount of such Unit from and including
the date of first issuance of the Units at a rate per annum equal to ____% (the
"Contract Fee Rate") (computed on the basis of a 360-day year of twelve 30-day
months and subject to deferral at the option of the Company as described in the
Purchase Contract Agreement). Contract Fees will be payable at the office of the
Purchase Contract Agent in The City of New York or, at the option of the
Company, by check mailed to the address of the Person entitled thereto at such
address as it appears on the Unit Register.


         The Company shall have the right, at any time prior to the Stock
Purchase Date, to defer the payment of any or all of the Contract Fees otherwise
payable on any Quarterly Payment Date, but only if the Company shall give the
Holders and the Purchase Contract Agent written notice of its election to defer
such payment (specifying the amount to be deferred) as provided in the Purchase
Contract Agreement.  Any Contract Fees so deferred shall bear additional
Contract Fees thereon at the rate of _____ per annum (and computed on the basis
of a 360-day year of twelve 30-day months), compounding on each succeeding
Quarterly Payment Date, until paid in full. Deferred Contract Fees (and
additional Contract Fees accrued thereon) shall be due on the next succeeding
Quarterly Payment Date except to the extent that payment is deferred pursuant to
the Purchase Contract Agreement.  No Contract Fees may be deferred to a date
that is after the Stock Purchase Date.

                  Pursuant to the Pledge Agreement, the Pledged Securities
constituting part of each Unit evidenced hereby have been pledged to the
Collateral Agent, for the benefit of the Company, to secure the obligations of
the Holder under the Purchase Contract comprising a portion of such Unit.


                                      A-2
<PAGE>   58
         Subject to and upon compliance with the provisions of the Purchase
Contract Agreement at the option of the Holder thereof, Purchase Contracts
underlying Units having an aggregate Stated Amount equal to $__________ per Unit
or an integral multiple thereof may be settled early ("Early Settlement") as
provided in the Purchase Contract Agreement.  In order to exercise the right to
effect Early Settlement with respect to any Purchase Contracts evidenced by this
Unit Certificate, the Holder of this Unit Certificate shall deliver this Unit
Certificate to the Purchase Contract Agent at the Corporate Trust Office duly
endorsed for transfer to the Company or in blank with the form of Election to
Settle Early set forth below duly completed and accompanied by payment in the
form of a certified or cashier's check payable to the order of the Company in
immediately available funds in an amount (the "Early Settlement Amount") equal
to (i) the product of (A) the Stated Amount per Unit times (B) the number of
Purchase Contracts with  respect to which the Holder has elected to effect Early
Settlement minus (ii) the aggregate amount of Contract Fees, if any, otherwise
payable on or prior to the immediately preceding Quarterly Payment Date deferred
at the option of the Company pursuant to the Purchase Contract Agreement and
remaining unpaid as of such immediately preceding Quarterly Payment Date plus
(iii) if such delivery is made with respect to any Purchase Contracts during the
period from the close of business on any Record Date next preceding any
Quarterly Payment Date to the opening of business on such Quarterly Payment
Date, an amount equal to the sum of (x) the Contract Fees payable on such
Quarterly Payment Date with respect to such Purchase Contracts plus (y) the
interest with respect to the related Underlying Securities payable on such
Quarterly Payment Date.  Upon Early Settlement of Purchase Contracts by a Holder
of the related Units, the Pledged Securities underlying such Units shall be
released from the Pledge as provided in the Pledge Agreement and the Holder
shall be entitled to receive, a number of Shares on account of each Purchase
Contract forming part of a Unit as to which Early Settlement is effected equal
to the Early Settlement Rate.  The Early Settlement Rate shall initially be
equal to __________ and shall be adjusted in the same manner and at the same
time as the Settlement Rate is adjusted as provided in the Purchase Contract
Agreement.

                  The transfer of any Unit Certificate will be registered and
Unit Certificates may be exchanged as provided in the Purchase Contract
Agreement. The Unit Registrar may require a Holder, among other things, to
furnish appropriate endorsements and transfer documents permitted by the
Purchase Contract Agreement. No service charge shall be required for any such
registration of transfer or exchange, but the Company and the Purchase Contract
Agent may require payment of a sum sufficient to cover any tax or other
governmental charge payable in connection therewith. Unless a Holder elects
Collateral Substitution, Early Settlement or Merger Early Settlement, for so
long as the Purchase Contract underlying a Unit remains in effect, such Unit
shall not be separable into its constituent parts, and the rights and
obligations of the Holder of such Unit in respect of the Pledged Securities and
Purchase Contract constituting such Unit may be transferred and exchanged only
as an integrated Unit.

                  Upon registration of transfer of this Unit Certificate, the
transferee shall be bound (without the necessity of any other action on the part
of such transferee) by the terms of the Purchase Contracts evidenced hereby and
by the Pledge Agreement, and the transferor shall be released from such
obligations. The Company covenants and agrees, and the Holder, by its acceptance
hereof, likewise covenants and agrees, to be bound by the provisions of this
paragraph.

                  The Holder of this Unit Certificate, by its acceptance hereof,
irrevocably authorizes the Purchase Contract Agent to enter into and perform the
related Purchase


                                      A-3
<PAGE>   59


Contracts evidenced hereby on its behalf as its attorney-in-fact, agrees to be
bound by the terms and provisions thereof, covenants and agrees to perform its
obligations under such Purchase Contracts, consents to the provisions of the
Principal Agreements, irrevocably authorizes and directs the Purchase Contract
Agent to enter into the Pledge Agreement on its behalf as its attorney-in-fact,
and consents to and agrees to be bound by the Pledge evidenced hereby pursuant
to the Pledge Agreement.

                  Subject to certain exceptions, the provisions of the Principal
Agreements may be amended with the consent of the Holders of at least a majority
of the Outstanding Units.

                  THE PURCHASE CONTRACTS SHALL FOR ALL PURPOSES BE GOVERNED BY,
AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK, WITHOUT
REGARD TO CONFLICTS OF LAWS PRINCIPLES THEREOF.

                  The Company, the Purchase Contract Agent and any agent of the
Company or the Purchase Contract Agent may treat the Person in whose name this
Unit Certificate is registered as the owner of the Units evidenced hereby for
the purpose of receiving payments of distributions or interest on the Pledged
Securities, receiving the rights and performing the obligations under the
Purchase Contracts and for all other purposes whatsoever, whether or not any
payments in respect thereof be overdue and notwithstanding any notice to the
contrary, and neither the Company, the Purchase Contract Agent nor any such
agent shall be affected by notice to the contrary.

                  THE PURCHASE CONTRACTS SHALL NOT, PRIOR TO THE SETTLEMENT
THEREOF, ENTITLE THE HOLDER TO ANY OF THE RIGHTS OF A HOLDER OF COMMON SHARES.

                  Copies of the Principal Agreements are available for
inspection at the offices of the Purchase Contract Agent.

                  Unless the certificate of authentication hereon has been
executed by the Purchase Contract Agent by manual signature, this Unit
Certificate shall not be entitled to any benefit under the Principal Agreements
or be valid or obligatory for any purpose.


                                      A-4
<PAGE>   60


                  IN WITNESS WHEREOF, the Company and the Holder hereby agree to
their respective obligations under the Purchase Contracts evidenced by this
instrument, and the Holder hereby acknowledges that the Pledged Securities
evidenced by this instrument are subject to the Pledge under the Pledge
Agreement.

                                            XO COMMUNICATIONS, INC.

                                            By:
                                               ---------------------------------
Attest:
        -----------------------------
                                            HOLDER SPECIFIED ABOVE

                                            By:                       ,
                                                ----------------------
                                            as Attorney-in-Fact of such Holder

                                            By:
                                                --------------------------------

Dated:

Purchase Contract Agent's Certificate of Authentication






                  This is one of the Unit Certificates referred to in the within
mentioned Purchase Contract Agreement.


                          ,
--------------------------
as Purchase Contract Agent


By:
    --------------------------------


                                      A-5
<PAGE>   61



                             SETTLEMENT INSTRUCTIONS


                  The undersigned Holder directs that a certificate for Shares
deliverable upon settlement on or after the Stock Purchase Date of the Purchase
Contracts underlying the number of Units evidenced by this Unit Certificate be
registered in the name of, and delivered, together with a check in payment for
any fractional share, to the undersigned at the address indicated below unless a
different name and address have been indicated below. If shares are to be
registered in the name of a Person other than the undersigned, the undersigned
will pay any transfer tax payable incident thereto.


Dated:
       -----------------------------------------------------------------------
                                                          Signature*


<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------
<S>                                                      <C>
If shares are to be registered in the name                                           REGISTERED HOLDER
of and delivered to a Person other than the
Holder, please print such Person's name and               Please print name and address of
address:                                                  Registered Holder:
-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------
                    Name                                                        Name
-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------
</TABLE>

-----------------------
*        Signature must be guaranteed by an eligible Guarantor Institution
         (banks, stockbrokers, savings and loan associations and credit unions)
         with membership in an approved signature medallion program pursuant to
         Securities and Exchange Commission Rule 17Ad-15 if Shares are to be
         delivered other than to, and in the name of, the registered Holder.



                                      A-6
<PAGE>   62


<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------
<S>                                                       <C>
If shares are to be registered in the name                                           REGISTERED HOLDER
of and delivered to a Person other than the
Holder, please print such Person's name and               Please print name and address of
address:                                                  Registered Holder:
-----------------------------------------------------------------------------------------------------------
                  Address                                                     Address
-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------
Social Security or other Taxpayer
Identification Number, if any
-----------------------------------------------------------------------------------------------------------
</TABLE>


                                      A-7
<PAGE>   63


<TABLE>
<S>                                                       <C>
                                                                                      REGISTERED HOLDER
If shares are to be registered in the name of
and delivered to a Person other than the Holder,          Please print name and address of Registered
please print such Person's name and address:              Holder:

                       Name                                                      Name



                      Address                                                   Address



Social Security or other Taxpayer
Identification Number, if any
</TABLE>



                                      A-8
<PAGE>   64





                            ELECTION TO SETTLE EARLY


                  The undersigned Holder directs that a certificate for Shares
deliverable upon settlement on or after the Early Settlement Date or the Merger
Early Settlement Date of the Purchase Contracts underlying the number of Units
evidenced by this Unit Certificate be registered in the name of, and delivered
to the undersigned at the address indicated below unless a different name and
address have been indicated below. If shares are to be registered in the name of
a Person other than the undersigned, the undersigned will pay any transfer tax
payable incident thereto.

Dated:
       -----------------------------------------------------------------------
                                                                Signature*


<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------
<S>                                                       <C>
If shares are to be registered in the name                                           REGISTERED HOLDER
of and delivered to a Person other than the
Holder, please print such Person's name and               Please print name and address of
address:                                                  Registered Holder:
-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------
                Name                                                        Name
-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------
               Address                                                     Address
-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------
Social Security or other Taxpayer
Identification Number, if any
-----------------------------------------------------------------------------------------------------------
</TABLE>


-----------------------------
*        Signature must be guaranteed by an eligible Guarantor Institution
         (banks, stockbrokers, savings and loan associations and credit unions)
         with membership in an approved signature medallion program pursuant to
         Securities and Exchange Commission Rule 17Ad-15 if Shares are to be
         delivered other than to, and in the name of, the registered Holder.



                                      C-2