Document:

<PAGE>   1

                                                                   EXHIBIT 10.5

                          STRATEGIC ALLIANCE AGREEMENT

THIS STRATEGIC ALLIANCE AGREEMENT (the "Agreement") is effective as of December
23, 1999 (the "Effective Date") and is by and between COLO.COM, a California
corporation with offices at 2000 Sierra Point Parkway, Suite 600, Brisbane,
California 94005 ("COLO.COM") and Nortel Networks Inc., a Delaware corporation
with offices at 2350 Lakeside Blvd., Richardson, Texas 75082 ("Nortel").

                                    RECITALS

1.      COLO.COM has developed a business plan to prepare site space and neutral
        central office locations for telecommunication and data service
        providers.

2.      Nortel has developed a broad array of telecommunications and data
        products and services that enable the development of voice and data
        networks.

3.      COLO.COM and Nortel desire to develop a mutually beneficial relationship
        whereby Nortel will purchase stock in COLO.COM and COLO.COM will provide
        Nortel a right of first refusal for a portion of each of its sites and
        purchase a minimum amount of equipment from Nortel.

4.      Contemporaneous with the execution of this Agreement, Nortel and
        COLO.COM will execute a Series C Stock Purchase Agreement (the "Stock
        Agreement"), the Amended and Restated Investor Rights Agreement (the
        "Investor Agreement"), and an Amended and Restated Right-of-First
        Refusal and Co-Sale Rights Agreement (the "Resale Agreement")
        (collectively, the "Stock Acquisition Agreements").

NOW THEREFORE, in consideration of the mutual promises and covenants contained
herein and other good and valuable consideration, the receipt and sufficiency of
which is hereby duly acknowledged by the parties, the parties hereby agree as
follows.

                             ARTICLE I - DEFINITIONS

The following capitalized terms not otherwise defined herein shall have the
following respective meanings:

"AFFILIATE" means, with respect to any referenced Person, a Person (i) which
directly or indirectly through one or more intermediaries controls, or is
controlled by, or is under common control with, such referenced Person. For
purposes of this definition, "control" when used with respect to any Person
means the possession, directly or indirectly, of the power to direct or cause
the direction of the management and policies of such Person, whether through the
ownership of voting securities, by agreement or otherwise; and the terms
"affiliated," "controlling" and "controlled" have meanings correlative to the
foregoing.

                                     Page 1

<PAGE>   2
"CONFIDENTIAL INFORMATION" means all information (whether in oral, written or
electronic form), including without limitation, business strategy and tactics,
specifications, drawings, documentation, know-how, manufacturing costs and
pricing information, of every kind or description which may be disclosed by one
party to the other party in connection with this Agreement, provided the
disclosing party shall clearly mark all such information disclosed in writing as
the confidential property of the disclosing party and, in the case of oral
disclosure, the disclosing party shall identify the confidential nature of any
such information at the time of such oral disclosure and shall provide a written
summary labeled as confidential of the orally disclosed confidential information
to the recipient within fifteen (15) business days of such disclosure.

"PERSON" means an individual, partnership, corporation, limited liability
company, trust or unincorporated organization or a government or agency or
political subdivision thereof.

"PRODUCT(s)" means, individually and collectively, the Network Hardware, Network
Software, and the Documentation associated with the Trial Network.

                        ARTICLE II - NORTEL'S OBLIGATIONS

        2.1 On the Effective Date, Nortel will execute the Stock Acquisition
Agreements and perform its obligations under the Stock Purchase Agreement.

        2.2 Nortel shall use commercially reasonable best efforts to negotiate
and execute an equipment sale and purchase agreement with COLO.COM by April 1,
2000, whereby Nortel will agree to sell to COLO.COM and COLO.COM will agree to
purchase Nortel equipment in an amount of no less than Five Million U.S. Dollars
($5,000,000) before December 31, 2001. Such purchase agreement will provide
COLO.COM no less than a 50% discount off of Nortel's published list price.

        2.3 Nortel, for every site in which (i) COLO.COM has site space
available and (ii) the customer is in the market to procure site space, shall
make a strong recommendation to such customer that it solicit a proposal from
COLO.COM for the site space.

        2.4 Within thirty (30) days after the Effective Date of this Agreement,
Nortel will identify and notify COLO.COM of the point of contact for COLO.COM as
the Nortel agent to manage the relationship between Nortel and COLO.COM.

                      ARTICLE III - COLO.COM'S OBLIGATIONS

        3.1 COLO.COM will issue Nortel 510,204 shares of Series C Preferred
Stock of COLO.COM common stock, representing eighty-five one hundredths of one
percent (.85%) of the aggregate outstanding shares of COLO.COM on a
fully-diluted basis on the Effective Date, substantially in accordance with the
terms and conditions of the Stock Purchase Agreement, the form of which is
attached hereto as Exhibit A.

        3.2 COLO.COM shall use commercially reasonable best efforts to negotiate
and execute the equipment sale and purchase agreement with Nortel described in
Section 2.2 above by April 1,

                                     Page 2

<PAGE>   3
2000.

        3.3 COLO.COM hereby grants Nortel a right-of-first refusal to lease site
space on twenty percent (20%) of the space intended to be leased at each site
prepared by COLO.COM. Such right-of-first refusal shall be: (i) transferable to
any Affiliate or customer of Nortel, (ii) survive for a period of eighteen
months (18) from the date of completion of each site, (iii) be available for
floor space and rack space cumulatively. When COLO.COM has leased or committed
to lease sixty percent (60%) the site, with the exception of the space reserved
for Nortel or its customers, COLO.COM may notify Nortel in writing that COLO.COM
has a customer to lease all or part of the reserved space. Upon receipt of such
notification, Nortel shall have thirty (30) calendar days to either commence
good-faith negotiations to lease the space or provide a customer to commence
good-faith negotiations to lease the space. Such lease negotiations shall be
completed no later than sixty (60) calendar days from the date of the receipt of
the notice. At the expiration of the thirty (30) calendar day period, the sixty
(60) calendar day period, or upon written notification by Nortel that it has
neither a customer nor the intent to lease the reserved space, COLO.COM in no
longer under any obligation to Nortel with respect to the space.

        Similarly, when COLO.COM has leased or committed to lease sixty percent
(70%) the site, with the exception of the remaining space reserved for Nortel or
its customers, COLO.COM may notify Nortel in writing that COLO.COM has a
customer to lease all or part of the remaining reserved space. Upon receipt of
such notification, Nortel shall have thirty (30) calendar days to either
commence good-faith negotiations to lease the space or provide a customer to
commence good-faith negotiations to lease the space. Such lease negotiations
shall be completed no later than sixty (60) calendar days from the date of the
receipt of the notice. Such lease negotiations shall be completed no later than
sixty (60) calendar days from the date of the receipt of the notice. At the
expiration of the thirty (30) calendar day period, the sixty (60) calendar day
period, or upon written notification by Nortel that it has neither a customer
nor the intent to lease the reserved space, COLO.COM in no longer under any
obligation to Nortel with respect to the remaining space.

        3.4 For every telecommunications or data equipment bid procurement
process whereby COLO.COM solicits bids for pricing and feature specifications,
COLO.COM shall provide Nortel adequate notice and opportunity to submit a
proposal to COLO.COM for the sale of Nortel equipment.

        3.5 If COLO.COM grants similar rights-of-first refusal to any Nortel
competitor, as listed on Exhibit B, or any Affiliate or successor of such
competitors, until such time as the stock in COLO.COM purchased pursuant to the
Stock Purchase Agreement is freely saleable under applicable securities laws on
a nationally recognized stock exchange, COLO.COM shall be obligated to
repurchase all of the COLO.COM stock held by Nortel at the then fair market
value.

        3.6 COLO.COM shall issue to Nortel a monthly report delineating the
locations available, the percentage vacancy for each site, the tenants and
percentage occupancy for such tenants of each site, and estimated completion
date for future sites. COLO.COM will also provide to Nortel the briefing package
to be provided to each member of the COLO.COM board of directors as well as the
minutes of the meeting of the COLO.COM board of directors within fifteen (15)
calendar days after the board meeting. In addition, within thirty (30) days
after the Effective Date of this

                                     Page 3

<PAGE>   4
Agreement, COLO.COM will identify and notify Nortel of the point of contact for
Nortel as the COLO.COM agent to manage the relationship between COLO.COM and
Nortel.

        3.7 COLO.COM agrees to, from time to time, designate an appropriate
executive to meet with a Nortel designated executive, at a mutually agreeable
time and location, to review and discuss the status of COLO.COM and any other
related aspects of the business relationship between the parties.

        3.8 COLO.COM shall, upon issuing new shares of common stock, make
available for purchase by Nortel, a sufficient number of shares of stock to
allow Nortel to retain the same percentage ownership in COLO.COM that Nortel has
at the time of the issuance of the new shares, and at the same price that the
shares are being offered all other investors.

        3.9 COLO.COM hereby represents and warrants to Nortel that the Stock
Acquisition Agreements are in substantially the same form as the other Investors
(as defined by the Stock Purchase Agreement) acquiring the Series C Preferred
Stock issued by COLO.COM.

                             ARTICLE IV - MARKETING

        4.1 The parties hereby agree to enter into a mutually agreeable
co-marketing agreement, including without limitation, provisions covering the
extent to which either party may use the other's name, trademarks and service
marks in marketing; and how the parties will allocate the costs associated with
developing and producing the co-branding marketing material and in marketing and
advertising the services.

        (a) The extent to which either party may use the other's name,
        trademarks and service marks in marketing the co-branded services;

        (b) Access to and use of customer lists of each party for marketing the
        co-branded services and any compensation therefor; and

        (c) How the parties will allocate the costs associated with developing
        and producing the co-branding marketing material and in marketing and
        advertising the services.

           ARTICLE V - LIABILITY FOR BODILY INJURY AND PROPERTY DAMAGE

        5.1 A party hereto shall defend the other party against any suit, claim,
or proceeding brought against the other party for direct damages due to bodily
injuries (including death) or damage to tangible property which allegedly result
from the negligence or willful misconduct of the defending party in the
performance of this Agreement. The defending party shall pay all litigation
costs, reasonable attorney's fees, settlement payments and such direct damages
awarded or resulting from any such suit, claim or proceeding. Each party's
indemnification obligation under this Section 5.1 shall include any claims by
any of its employees brought against the other party.

                                     Page 4

<PAGE>   5
                ARTICLE VI - REMEDIES AND LIMITATION OF LIABILITY

        6.1 In the event of any material breach of this Agreement which shall
continue for thirty (30) or more days after written notice of such breach
(including a reasonably detailed statement of the nature of such breach) shall
have been given to the breaching party by the aggrieved party, the aggrieved
party shall be entitled at its option to avail itself of any and all remedies
available at law or equity, except as otherwise limited in this Agreement. In
addition, if the parties, after good faith negotiations, have not executed an
equipment sale and purchase agreement within thirty (30) days of the date
specified in Sections 2.2 and 3.2 above, then COLO.COM shall be obligated, at
Nortel's option, purchase at Nortel's purchase price or fair market value
(whichever is greater), all of the stock in COLO.COM purchased by Nortel under
the Stock Purchase Agreement.

        6.2 Nothing contained in Section 6.1 or elsewhere in this Agreement
shall make Nortel or COLO.COM liable to the other for any indirect, incidental,
punitive, special, or consequential damages of any nature whatsoever for any
breach of this Agreement whether the claims for such damages arise in tort
(including negligence regardless of degree of fault), contract, or otherwise.

        6.3 Any action for breach of this Agreement or to enforce any right
hereunder shall be commenced within two (2) years after the cause of action
accrues or it shall be deemed waived and barred.

                       ARTICLE VII - TERM AND TERMINATION

        7.1 This Agreement will be in effect from the Effective Date for period
of two (2) years.

        7.2 Either party may delay performance under this Agreement or terminate
this Agreement, in whole or in part, in the event of a default by the other,
provided that the non-defaulting party so advises the defaulting party in
writing of the event of alleged default and the defaulting party does not remedy
the alleged default within thirty (30) days after written notice thereof. If the
alleged default is not capable of being remedied within thirty (30) days, the
defaulting party must commence to remedy the alleged default within such thirty
(30) day period and provide to the non-defaulting party a plan for timely
remedying the alleged default in order to avoid termination. A default shall
include:

                (a) a party's insolvency or initiation of bankruptcy or
                receivership proceedings by or against a party or the execution
                of an assignment for the benefit of creditors; or

                (b) either party's material breach of any of the terms or
                conditions hereof, including without limitation, the failure to
                make any payment when due.

        7.3 The expiration or termination of this Agreement for any cause shall
not release either party from:

                                     Page 5

<PAGE>   6
                (i) any obligations and duties remaining under any other
                agreement entered into prior to such expiration or termination;

                (ii) any liability which at the time of expiration or
                termination has already accrued to the other party, or, which
                thereafter may accrue in respect to any event prior to
                expiration or termination; or

                (iii) any liability from any obligation specified in Section
                9.13 below to survive expiration or termination.

                         ARTICLE VIII - CONFIDENTIALITY

        8.1 Each party which receives the other party's Confidential Information
shall use reasonable care to hold such Confidential Information in confidence
and not disclose such Confidential Information to anyone other than to its
employees and employees of an COLO.COM Affiliate or Nortel Affiliate, as
applicable, with a need to know. A party that receives the other party's
Confidential Information shall not reproduce such Confidential Information,
except to the extent reasonably required for the performance of its obligations
pursuant to this Agreement and in connection with any permitted use of such
Confidential Information.

        8.2 COLO.COM shall take reasonable care to use Nortel's Confidential
Information only for study, operating, or maintenance purposes in connection
with COLO.COM's use of Products furnished by Nortel pursuant to this Agreement.

        8.3 The obligations of either party pursuant to this Article VIII shall
not extend to any Confidential Information which a recipient can demonstrate
through written documentation was already known to the recipient prior to its
disclosure to the recipient and without confidential obligations was known or
generally available to the public at the time of disclosure to the recipient,
becomes known or generally available to the public (other than by act of the
recipient) subsequent to its disclosure to the recipient, is disclosed or made
available in writing to the recipient by a third party having a bona fide right
to do so and without similar confidentiality obligations, is independently
developed by recipient, or is required to be disclosed by subpoena or other
process of law, provided that the recipient shall notify the disclosing party
promptly of any such subpoena or other process of law requiring disclosure.

        8.4 The parties agree that each will keep the existence and contents of
this Agreement completely confidential, and will not publicize or disclose the
conditions, or terms or contents of this Agreement in any manner, whether in
writing or orally, to any person, whether directly or indirectly, except either
party may disclose the terms of this Agreement (a) to its legal counsel and
accountants, (b) to the limited extent required by federal securities laws, (c)
to prospective investors, or other sources of funding, that are bound to
confidentiality provisions at least as restrictive as those contained herein or
(d) pursuant to a court order or governmental authority as required by law. The
disclosure of the aforementioned information, in violation of this provision,
shall be deemed to be a material breach of this Agreement.

                                     Page 6

<PAGE>   7
                           ARTICLE IX - MISCELLANEOUS

        9.1 Applicable Law - The validity, construction and performance of this
Agreement shall be governed by and interpreted in accordance with the laws of
the State of California, except for its rules with regard to the conflict of
laws of any jurisdiction.

        9.2 Effects of Headings - All headings used herein are for index and
reference purposes only, and shall not be given any substantive effect. This
Agreement has been created jointly by the parties and no rule of construction
requiring interpretation against the drafter of this Agreement shall apply in
its interpretation.

        9.3 Assignment - Other than as explicitly stated below, neither party
may assign or transfer this Agreement or any of its rights hereunder without the
prior written consent of the other party, such consent not to be unreasonably
withheld or delayed. No consent shall be required for any assignment or transfer
by a party to its Affiliates of all or any part of this Agreement or of such
party's rights hereunder.

        9.4 Non-Waiver - The failure by either party hereto at any time to
require performance by the other party or to claim a breach of any provision of
this Agreement shall not be construed as affecting any subsequent breach or the
right to require the performance with respect thereto or to claim a breach with
respect thereto.

        9.5 Relationship of the Parties - The provisions of this Agreement shall
not be construed to establish any form of partnership, agency or joint venture
of any kind between Nortel and COLO.COM, nor to constitute either party as the
agent, employee or legal representative of the other. All persons furnished by
either party to accomplish the intent of this Agreement shall be considered
solely as the furnishing party's employees or agents and the furnishing party
shall be solely responsible for compliance with respect to its employees with
all laws, rules and regulations involving, but not limited to, employment of
labor, hours of labor, working conditions, workers' compensation, payment of
wages, and withholding and payment of applicable taxes, including without
limitation, income taxes, unemployment taxes, and social security taxes.

        9.6 Force Majeure - If the performance by a party of any of its
obligations under this Agreement shall be interfered with by reason of any
circumstances beyond the reasonable control of that party, including without
limitation, fire, explosion, acts of God, war, revolution, civil commotion,
unavailability of supplies or sources of energy, power failure, breakdown of
machinery, delays regarding zoning, easements or deed restrictions, any legal
proceedings between parties unrelated to the parties hereto or labor
difficulties, including without limitation, strikes, slowdowns, picketing or
boycotts, then that party shall be excused from such performance for a period
equal to the delay resulting from the applicable circumstances and such
additional period as may be reasonably necessary to allow that party to resume
its performance. With respect to labor difficulties as described above, a party
shall not be obligated to accede to any demands being made by employees or other
personnel.

        9.7 Expenses - Each party shall bear its own expenses in connection with
the drafting and negotiation of this Agreement and the related agreements as
contemplated herein.

                                     Page 7

<PAGE>   8
        9.8. Notice - All notices required or permitted to be given hereunder
shall be in writing and shall be deemed given when delivered (i) by hand; or
(ii) by facsimile transmission (confirming the same by mail); or (iii) by
certified or next-day mail addressed as follows:

        If to COLO.COM:

        COLO.COM
        2000 Sierra Point Parkway, Suite 600
        Brisbane, California  94005
        Attention:
                  -------------------------------
        Facsimile:
                  -------------------------------

        If to Nortel:

        Nortel Networks Inc.
        2350 Lakeside Blvd
        Richardson, Texas  75082
        Attention:  Mr. James Bartoszewicz
        Facsimile:  972/684-3994

Either party hereto may change its address by a notice given to the other party
hereto in the manner set forth above.

        9.9 Information and Documentation - COLO.COM shall provide any
information and/or documentation that Nortel reasonably requests from COLO.COM
and that is necessary for Nortel to properly perform any of its obligations
hereunder. Such information shall be provided in a form reasonably specified by
Nortel by the dates reasonably specified by Nortel.

        9.10 Severability - If any provision of this Agreement is declared or
determined to be invalid or unenforceable under applicable law, the remaining
provisions shall continue in full force and effect and the parties shall
substitute for the invalid provision a valid provision which most closely
approximates the economic effect and intent of the invalid provision.

        9.11 Modification of Agreement - No addition to or modification of this
Agreement shall be effective or binding on either of the parties hereto unless
reduced to writing and executed by the respective duly authorized
representatives of each of the parties hereto.

        9.12 Entire Agreement - This Agreement, including the Exhibits and
Annexes which are attached hereto and incorporated herein, comprises all the
terms, conditions and agreements of the parties hereto with respect to the
subject matter hereof and supersedes all previous negotiations, proposals,
commitments, writings, publications and understandings of any nature whatsoever.
No Exhibits or Annexes modified or created subsequent to the execution of this
Agreement shall be deemed to be incorporated into this Agreement unless mutually
agreed in a writing and executed or initialed by a duly authorized
representative of each party. The parties hereby acknowledge and agree that
neither has relied on any representations or warranties other than those
expressly set forth in this Agreement.

                                     Page 8

<PAGE>   9
        9.13 Survivorship - Any terms of this Agreement, which by their nature
are intended to survive, including without limitation, Articles 5, 7, and 8
shall survive the termination or expiration of this Agreement.

                         [Signatures on following page]

                                     Page 9

<PAGE>   10
        IN WITNESS whereof the parties have executed this Agreement effective as
of the date first shown above.

COLO.COM                                  NORTEL NETWORKS INC.

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

Name:                                     Name:  James Bartoszewicz
     -----------------------------             -----------------------------
Title:                                    Title: Vice-President
      ---------------------------               ----------------------------

<PAGE>   11
                                    EXHIBIT A

                        FORM OF STOCK PURCHASE AGREEMENT

<PAGE>   12
                                    EXHIBIT B

                              COMPETITORS OF NORTEL

Lucent Technologies Inc.
Cisco Systems Inc.
Alcatel
Nokia
Siemens
Sonus
Taqua Systems<PAGE>   1

                                                                    Exhibit 10.6

                   COLO.COM AND NEXTLINK DEFINITIVE AGREEMENT

This Definitive Agreement ("Agreement") is entered into this 23rd day of
December 1999 (the "Effective Date") by and between NEXTLINK COMMUNICATIONS,
Inc., a Delaware corporation ("NEXTLINK"), and COLO.COM, a California
corporation ("COLO"). NEXTLINK and COLO are referred to herein separately as
"Party" and together as "Parties." The Effective Date of this Agreement is the
same date as the closing date of the COLO Series C preferred stock offering
between COLO and NEXTLINK.

For good and valuable consideration, COLO and NEXTLINK hereby agree as follows:

A.   DEFINITIONS.

     1.   Carrier Termination Equipment Space: means a carrier termination
          equipment bay for which NEXTLINK has an Option.

     2.   Colocation Space: means colocation space from 500 to 1,000 square feet
          for which NEXTLINK has an Option.

     3.   Customary Services: means those services that COLO provides to its own
          termination space or to the termination space of its carrier or
          non-carrier customers, including power (electricity, N+1 UPS system
          deployed in parallel redundant configuration, and generator backup to
          100% of customer peak load), conditioning (data grade HVAC, constant
          72 degree ambient air temperature, and constant 45% humidity), state
          of the art fire suppression system, security and smart hands, and such
          other services set forth on the attachment to this Agreement.

     4.   Neutral Central Office ("NCO"): means real property and improvements
          that are used or planned to be used, as the context of the provision
          requires, by COLO as a carrier-neutral central office for colocation
          and for locating and interconnecting servers, routers, data
          communications equipment, telecommunications equipment and other
          equipment used by COLO and/or its customers.

     5.   Network: means the terrestrial telecommunications network of one of
          the Parties, as the context of the provision requires or as
          contemplated under this Agreement, including facilities leased or
          acquired from other carriers.

     6.   Option: means the option NEXTLINK has under this Agreement to lease
          each of the Telecommunication Equipment Spaces described in Section F.

     7.   Prioritized Option/Partners: means a partner that is strategic to COLO
          and provides substantial economic, business and/or marketing benefit
          to COLO.

     8.   Tower Rights: means a annually agreeable amount of wireless
          communication tower space satisfactory for NEXTLINK's technical needs
          for which NEXTLINK has an Option.

     9.   Space Agreement: means an agreement for Telecommunications Equipment
          Space entered into between the Parties as provided in Section F below,
          including the Colocation Space and Carrier Termination Equipment
          Space Agreement (Exhibit A):

     10.  Telecommunications Equipment Space: means the space COLO shall provide
          to NEXTLINK in COLO's NCOs as provided in Section F below.

B.   TERM.

     The term of this Agreement shall be 5 years commencing on the Effective
Date. NEXTLINK shall have the right to renew this Agreement for 2 additional
5-year terms by giving COLO written notice at least 90 days before the
then-current term expires. As used herein, the word "Term" shall mean the
initial term and any renewal terms.

CONFIDENTIAL                      Page 1 of 12                 December 23, 1999

<PAGE>   2
C.   NEXTLINK EQUITY INVESTMENT.

     By means of a separate Series C Preferred Stock Purchase Agreement entered
into concurrently herewith, NEXTLINK shall agree to invest $5,000,000 in COLO
in a private placement of equity securities by purchasing approximately 500,000
shares of COLO's Series C Preferred Stock.

D.   COLO'S NEUTRAL CENTRAL OFFICES.

     1.   COLO represents and warrants that, as of the date of this Agreement,
it owns or is authorized to control the NCOs listed as "Current NCOs" on
Attachment 1 and COLO plans to own or obtain authorization to control the NCOs
listed as "Planned NCOs" on Attachment 1. COLO shall notify NEXTLINK promptly
after COLO obtains additional NCOs, including a description of each new NCO. In
addition, each quarter COLO shall provide an electronic copy of an updated
Attachment 1 to NEXTLINK to the e-mail address listed in Section I.12 below.

     2.   COLO represents and warrants that it shall own or control at least 43
domestic and 13 international operational NCOs by December 31, 2001. In
addition, COLO represents and warrants that it has sufficient Colocation Space
and Carrier Termination Equipment Space in its Current NCOs to allow NEXTLINK to
exercise its Options to such space (with the exception of Colocation Space in
the 8619 Westwood, Vienna, VA NCO) and shall have sufficient Colocation Space
and Carrier Termination Equipment Space available to NEXTLINK as contemplated
under this Agreement at NCOs that become Current NCOs during the term of this
Agreement. COLO further represents and warrants that it has not granted any
priorities or options superior to NEXTLINK's priorities and Options under this
Agreement.

     3.   COLO represents and warrants that as of the date it notifies NEXTLINK
that an NCO is a Current NCO, COLO has good marketable fee simple title or has
a valid, enforceable leasehold interest or a valid, enforceable license
authorizing COLO to control the NCO and the property upon which the NCO is
located to such an extent as permits COLO to perform fully its obligations
under this Agreement.

E.   CONNECTION OF NEXTLINK'S NETWORK TO COLO'S NCOs.

     1.   COLO shall grant to NEXTLINK a warrant to purchase up to 300,000
shares of COLO's Series C Preferred ("Warrant Shares"), as appropriately
adjusted for any future stock splits, stock combinations or stock dividends or
similar transactions affecting COLO's capital stock, in a separate Warrant
Agreement entered into concurrently herewith (the "Warrant"). The Warrant shall
be subject to the following terms:

          a.   The Warrant shall have a term of 5 years from the date the
Warrant is issued;

          b.   For each NCO to which NEXTLINK initiates the process of
interconnecting to its Network on or prior to March 15, 2000, up to a total of
ten (10) NCOs, NEXTLINK shall have the right to exercise its purchase rights
represented by the Warrant with respect to 30,000 Warrant Shares. NEXTLINK
shall be deemed to have initiated the interconnection process for a NCO upon
its delivery to COLO of a copy of the business case prepared by NEXTLINK's
National Sales group for the applicable NEXTLINK local operating subsidiary
with respect to the interconnection of the NCO in question. COLO agrees and
acknowledges that each business case is subject to the approval of, and
revision and modification by, the local operating subsidiary. NEXTLINK in good
faith will exercise commercially reasonable efforts to complete the
interconnection of its Network to each such NCO site within nine (9) months
from the date that the interconnection process is deemed to be initiated
pursuant to this paragraph.

          c.   The exercise price per share of COLO's Warrant Stock shall be
Ten Dollars ($10.00); and

          d.   In lieu of exercising the Warrant for cash, NEXTLINK may, at its
option, pay the exercise price on a next exercise or cashless basis.

CONFIDENTIAL                      Page 2 of 12                 December 23, 1999

<PAGE>   3
     2.   NEXTLINK in good faith will exercise commercially reasonable efforts
to interconnect its Network to ten (10) NCO sites, within two (2) years from the
date of this Agreement, in addition to the ten (10) NCOs to which it initiates
the interconnection process, pursuant to paragraph 1 of this section. NEXTLINK
may choose NCO sites that are listed on Attachment 1 or NCOs established
subsequent to the date of this Agreement. COLO will regularly apprise NEXTLINK
of newly leased NCO sites and the status of planned NCO sites. For each NCO
that NEXTLINK designates for interconnection, the Parties shall mutually agree
upon the demarcation point, and COLO shall provide NEXTLINK with reasonable
access for NEXTLINK to bring its facilities into the NCO for interconnection and
to repair, replace and maintain those facilities.

     3.   COLO shall use its reasonable efforts to acquire or obtain
authorization to control any NCOs in locations selected by NEXTLINK under this
Section E that are not Current NCOs as listed on Attachment 1. COLO shall
notify NEXTLINK in writing when COLO has acquired or obtained authorization to
control an NCO that NEXTLINK has selected, with copies of the documents
evidencing such acquisition or authorization. When NEXTLINK receives notice
from COLO that COLO has obtained or been authorized to control an NCO that
NEXTLINK has requested for interconnection, NEXTLINK shall connect its network
to that NCO within 9 months after the date it received such notice.

F.   COLO'S PROVISION OF TELECOMMUNICATIONS EQUIPMENT SPACE

     1.   Options. In each of COLO's NCOs (except in the 8619 Westwood, Vienna,
VA NCO as to Colocation Space only), NEXTLINK and its affiliates shall have an
Option on the each of the following:

          a.   Colocation Space. NEXTLINK may, at its option, take down
Colocation Space in increments of 100 square feet;

          b.   Carrier Termination Equipment Space. COLO shall provide, at its
sole cost and expense, 4 adjacent, full-height equipment racks in each Carrier
Termination Equipment Space; and

          c.   Wireless Communication Tower Space. COLO shall use its
reasonable efforts to obtain Wireless Communication Tower Space for NEXTLINK's
technical requirements at all NCOs, provided that NEXTLINK has given COLO
reasonable advance notice of its wireless communication tower requirements
(i.e., technical and space requirements) to COLO. NEXTLINK may, but shall not
be obligated to, assist COLO in its efforts to obtain those roof rights.

     2.   Exercise of Options.

          a.   Available Space. COLO shall give NEXTLINK written notice for
each NCO whenever COLO reaches 70% occupancy and/or receives a bona fide
offer(s) for 70% of the colocation space in a given site. In that written
notice, COLO shall request that NEXTLINK declare within 30 days from the date
of the request whether it intends to exercise its right to up to 1000 square
feet of Telecommunications Equipment Space. COLO also shall give NEXTLINK
written notice for each NCO of the availability of any Tower Rights in that NCO
and, subsequently, upon reaching 70% occupancy and/or the receipt of a bona
fide offer(s) for 70% of the Tower Rights available at an NCO. If NEXTLINK
fails to respond within the 30-day period, NEXTLINK shall be deemed to have
waived the Option and COLO shall be free to offer the Equipment and Tower Space
to other interested Parties. NEXTLINK's right to last available space under
this Section F.2a shall expire three years after execution of this Agreement.

          b.   Last Available Space. COLO shall give NEXTLINK written notice
for each NCO whenever COLO shall have received a written request from a carrier
seeking to occupy the last Carrier Termination Space (POP Room) in such NCO.
COLO shall request that NEXTLINK declare within 30 days from the date of the
request whether it intends to exercise its rights to the last Carrier
Termination Space. If NEXTLINK fails to respond within the 30-day period,
NEXTLINK shall be deemed to have waived the Option and COLO shall be free to
offer Carrier Termination space to other interested Parties. NEXTLINK's right
to last available space under Section F.2.b shall run for the term of this
Agreement.

          c.   Notice of Exercise of Option. NEXTLINK may exercise any Option
by giving COLO written notice specifying the NCO and the type and size of the
space, provided, however, that the size and configuration of any Tower Rights
shall be mutually agreed to by the Parties.

CONFIDENTIAL                      Page 3 of 12                 December 23, 1999

<PAGE>   4
          d. Space Agreements. For each space for which NEXTLINK exercises an
Option, the Parties shall enter into the appropriate Space Agreement, as
follows, within 10 days of the date NEXTLINK exercises its option. The
Colocation Space Agreement and Carrier Termination Equipment Space Agreement is
attached hereto as Exhibit A; and the Tower Rights Agreement is attached hereto
as Exhibit B (each a "Space Agreement").

     3.   Customary Services. COLO shall provide all its Customary Services to
Carrier Termination Equipment Space for which NEXTLINK exercises its Option, at
no additional charge. Other Telecommunications Equipment Space will be provided
with Customary Services at the rates provided in Attachment 2.

     4.   Payment for Telecommunications Equipment Space.

          a. Rental Rate. The rental rate for the Telecommunications Equipment
Space shall be the rates listed in Attachment 2; provided, however, that if COLO
offers or gives a lower rate to a Prioritized Option/Partner, those lower rates
shall apply to the Telecommunications Equipment Rate. Within 5 days after
NEXTLINK exercises an Option, COLO shall provide NEXTLINK with a list of the
rates it has given in the previous 12 months and the rates it is then-currently
offering to its Prioritized Option/Partners. NEXTLINK shall have 10 days to
notify COLO, either (i) affirming the rental rate (either the rate listed in
Attachment 2 or the rate provided to other customers as stated by COLO) or (ii)
disputing the rental rate proposed by COLO for the Telecommunications Equipment
Space. If NEXTLINK disputes the rental rate provided by COLO, NEXTLINK shall pay
the lowest rate proposed by COLO pending resolution of the dispute of COLO
provides a better rate to itself or another customer during the terms of a Space
Agreement between the Parties, NEXTLINK shall be entitled to that same rate as
of the date that better rate is granted.

          b. Obligations to Pay Rent. NEXTLINK's obligation to pay rent to COLO
shall begin: (i) for Colocation Space, the date that is 45 days after the date
that NEXTLINK exercises its option to the space, provided that the Parties have
timely entered into a Colocation Space Agreement; (ii) for Carrier Termination
Equipment Space and Wireless Communication Tower Space, the date that is 30
days after NEXTLINK exercises its option to the space, provided that the
Parties have timely entered into the applicable Space Agreement.

          c. Prepaid Carrier Termination Space. NEXTLINK hereby receives a
credit entitling it to free rent for 40 Carrier Termination Equipment Spaces at
NCOs selected by NEXTLINK. The rent credit for each space shall apply for 24
months from the date that NEXTLINK first occupies that space ("Rent Credit
Period"). Within 25 days before the end of the Rent Credit Period, COLO shall
provide NEXTLINK with a list of the rates it has given in the previous 12
months and the rates it is then-currently offering to its Prioritized
Option/Partners for Carrier Termination Equipment Spaces. NEXTLINK shall notify
COLO within 10 days whether NEXTLINK wishes to terminate a Carrier Termination
Equipment Space Agreement after the Rent Credit Period, in which case the
applicable Space Agreement shall terminate effective as of the end of the Rent
Credit Period. If NEXTLINK does not terminate the Carrier Termination Equipment
Space Agreement, Section F.4.a shall apply to finalize the rental rate.

G.   RESELLER PRIVILEGES.

     Upon mutual agreement of the Parties, NEXTLINK shall have the right to
resell COLO's services under COLO's standard reseller agreement, and under the
then-best reseller discounts and/or commissions offered or given by COLO to any
of its other customers.

H.   PREFERRED PROVIDER.

     In the event that COLO decides to interconnect and internetwork its NCOs
or to resell transport and carrier services, COLO will make NEXTLINK its
preferred provider for the required transport if NEXTLINK satisfies COLO's
technical and operational requirements and offers reasonable installation
intervals and market pricing. NEXTLINK shall provide such transport arrangements
to COLO pursuant to its then generally applicable terms and conditions for such
services.

I.   MISCELLANEOUS.

     1.   Confidentiality. Both Parties shall use reasonable and good faith
efforts to maintain, except as required by law, the confidentiality of this
Agreement (including all Attachments and Exhibits), the transactions proposed
in this Agreement, and confidential information shared with each other under
this Agreement. Any communications about the transactions contemplated herein
other than to key management employees, shall be jointly coordinated between
the Parties.

CONFIDENTIAL                            Page 4 of 12       December 23, 1999

<PAGE>   5

      2.    Limitation of Liability. Neither Party shall be liable to the other
Party, or to the other Party for any liability to a third party as provided in
Section I.3, for any indirect, consequential, special, incidental, reliance, or
punitive damages of any kind or nature whatsoever (including but not limited to
any lost profits, lost revenues, lost savings, or harm to business) arising out
of this Agreement, regardless of the foreseeability thereof.

      3.    Indemnification.

            a.    COLO shall indemnify, defend and hold harmless NEXTLINK and
its subsidiaries, affiliates, employees, directors, officers, and agents from
and against all claims, demands, actions, causes of actions, damages,
liabilities, losses, and expenses (including reasonable attorney's fees)
incurred as a result of (i) claims for libel, slander, infringement of
copyright or unauthorized use of trademark, trade name or service mark arising
out of the transactions contemplated herein; (ii) claims for patent
infringement arising from combining or connection of facilities to NEXTLINK's
Network; and (iii) claims for damage to property and/or personal injuries
(including death) arising out of COLO's negligence or willful act or omission.

            b.    NEXTLINK shall indemnify, defend and hold harmless COLO and
its subsidiaries, affiliates, employees, directors, officers, and agents from
and against all claims, demands, actions, causes of actions, damages,
liabilities, losses, and expenses (including reasonable attorney's fees)
incurred as a result of (i) claims for libel, slander, infringement of
copyright or unauthorized use of trademark, trade name or service mark arising
out of the transactions contemplated herein; (ii) claims for patent
infringement arising from combining or connection of facilities to COLO's
Network; and (iii) claims for damage to property and/or personal injuries
(including death) arising out of NEXTLINK's negligence or willful act or
omission.

            c.    The warranties set forth in this Agreement constitute the
only warranties with respect to this Agreement. SUCH WARRANTIES ARE IN LIEU OF
ALL OTHER WARRANTIES, WRITTEN OR ORAL, STATUTORY, EXPRESS OR IMPLIED,
INCLUDING, WITHOUT LIMITATION, THE WARRANTY OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE OR USE.

      4.    Organizational Representations and Warranties. NEXTLINK represents
and warrants to COLO that it is an entity, duly organized, validly existing and
in good standing under the laws of its origin, with all requisite power to
enter into and perform its obligations under this Agreement in accordance with
its terms. COLO represents and warrants that it is an entity, duly organized,
validly existing and in good standing under the laws of its origin, with all
requisite power to enter into and perform its obligations under this Agreement
in accordance with its terms.

      5.    Assignment. This Agreement may not be assigned by either Party
without the prior written consent of the other Party, which shall not be
unreasonably withheld.

      6.    Amendment. This Agreement shall be amended only by written
agreement signed by authorized representatives of both Parties.

      7.    Governing Law Venue. This Agreement shall be interpreted according
to the laws of the state of Delaware, without regard to choice of law
principles. Except as otherwise provided in Section I.9 below, venue shall be
in the state of California.

      8.    Attorney Fees. In any claims under this Agreement, each side shall
bear its own costs and attorneys fees.

      9.    Dispute Resolution. In the event of a monetary dispute between COLO
and NEXTLINK concerning a principal amount in controversy of less than $50,000
(specifically excluding all nonmonetary claims or disputes) arising out of the
Agreement, COLO and NEXTLINK shall attempt to resolve such dispute through
negotiations for thirty (30) days. If

CONFIDENTIAL                    Page 5 of 12        December 23, 1999

<PAGE>   6
event that any Party shall fail to so appoint an arbitrator, the arbitrator
appointed by the other Party shall be the sole arbitrator. If two arbitrators
shall be so appointed, such two arbitrators shall, within ten (10) additional
days of the appointment of the last appointed arbitrator, select a third
arbitrator with the same qualifications. If the two arbitrators are unable to
agree concerning the third arbitrator, such matter shall be submitted to the
presiding judge of a court of competent jurisdiction in the circuit, district,
county (or other comparable geographic designation) in which the Building is
located and the selection of the third arbitrator by such presiding judge shall
be binding upon COLO and NEXTLINK. Within thirty (30) days of the selection of
the third arbitrator (or, if applicable, the sole arbitrator) or within such
longer, but reasonable period of time permitted by a majority of arbitrators
(or the sole arbitrator, if applicable), each Party shall make a written
submission to the arbitrator(s), including the Party's position concerning the
dispute and proposed resolution thereof, and, within twenty (20) days of
receipt of such submissions, the arbitrator(s) shall select the proposed
resolution that is most appropriate, taking into account the terms and
provisions of the Agreement, applicable law, and other relevant facts and
circumstances. The decision of any two arbitrators (if three arbitrators shall
have been selected) shall be binding on COLO and NEXTLINK; if only one
arbitrator shall have been selected, the decision of the sole arbitrator shall
be binding on COLO and NEXTLINK. The compensation of the arbitrator(s) shall be
borne equally by COLO and NEXTLINK. The Parties shall reasonably cooperate to
exchange documents or information necessary in order to prepare the submissions
required hereunder; provided, however, that the COLO and NEXTLINK acknowledge
and agree that a principal purpose of such arbitration is to avoid, if
possible, and to minimize the costs of, document and information exchange. In
the event of any dispute concerning the exchange of documentation or
information necessary in order to prepare the required submissions, such dispute
shall be submitted to the arbitrator(s) and the decision of a majority of the
arbitrators shall be conclusive on COLO and NEXTLINK.

     10.  No Waiver. The failure of a Party to insist on compliance with any of
the terms and conditions of this Agreement shall not be considered the waiver
of any other term or condition of this Agreement.

     11.  Entire Agreement. This Agreement sets forth the entire understanding
of the Parties and supersedes any and all prior agreements, arrangements or
understanding relating to the subject matter hereof.

     12.  Notices. Except as otherwise expressly provided herein, notices under
this Agreement shall be in writing and delivered by personal delivery,
overnight delivery service, or by certified mail, return receipt requested, to
the persons whose names and addresses appear below. Such notice shall be
effective on the date of receipt or refusal thereof by the receiving Party.

          COLO:                    NEXTLINK

COLO.COM                                NEXTLINK Communications Inc.
2000 Sierra Point Parkway               14811 N. Kirkland Blvd., Suite 100
Brisbane, CA 94005                      Scottsdale, AZ 85254
Attn: General Counsel                   Attn: Vice President, National Sales

                                      with a copy to:
                                      NEXTLINK Communications, Inc.
                                      14811 Farm Credit Drive
                                      McLean, VA 22102
                                      Attn: General Counsel

13.  Attachments and Exhibits. The following attachments and exhibits are
incorporated in this Agreement.

     Attachment 1 - COLO's Neutral Central Offices
     Attachment 2 - Prioritized Option/Partners Rental Rates
     Exhibit A - Colocation and Carrier Termination Equipment Space Agreement
     Exhibit B - Tower Rights Agreement

IN WITNESS WHEREOF, the Parties hereto have executed this Agreement as of the
day and year first written above.

CONFIDENTIAL                             Page 6 of 12      December 23, 1999

<PAGE>   7
NEXTLINK Communications, Inc.                COLO.COM

By: /s/ [Signature Illegible]                By: /s/ [Signature Illegible]
    -------------------------                   --------------------------

Title: Asst. Sec.                            Title: S.U.P. Operations/Admin
       ----------------------                     ------------------------

Date: 2/23/99                                Date: 12-23-95
     ------------------------                     ------------------------

CONFIDENTIAL                      Page 7 of 12                 December 23, 1999
<PAGE>   8
                                  ATTACHMENT 1

     COLO's Neutral Central Offices [Insert Lists as previously provided in Due
Diligence to Hank Koerner]

Current NCOs:

1.   Los Angeles (Garland Bldg. 1200 W. 7th Street, Los Angeles CA 90017)

2.   Washington DC (8619 Westwood Center Drive, Vienna, VA 22182)

3.   Chicago (725 Wells, Chicago, IL 60607)

4.   San Francisco (1400 65th Street, Emeryville, CA 94608)

5.   Milwaukee (Wells Bldg. 324, E. Wisconsin, Milwaukee, WI 53202)

Planned NCOs:

1.   Dallas (Infomart, 1950 Stemmons Freeway, Dallas, TX 75207)

2.   Chicago (800 Jorie Blvd., Oak Brook, IL 60523)

3.   San Francisco (650 Townsend, San Francisco, CA 94103)

4.   Fort Worth (Burnett Plaza - 801 Cherry Street, Fort Worth, TX 76102)

5.   New York (395 Hudson Street, New York, NY 10014)

6.   Las Vegas (7185 Pollock Drive, Las Vegas, NV 89119)

                                  Page 8 of 12
<PAGE>   9
                                  ATTACHMENT 2

                    PRIORITIZED OPTION/PARTNERS RENTAL RATES

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------
TYPE OF SPACE                      LOCATION              RENTAL RATE PER MONTH
---------------------------------------------------------------------------------------
<S>                                <C>            <C>
  Prepaid Carrier Termination                                  $700/rack
                                   ----------------------------------------------------

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

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

---------------------------------------------------------------------------------------
         Colocation                                40% discount off following rates:

                                                            $1,400 full rack
                                                            $1,100 half rack
                                                            8x7 cage $4,600
                                                           10x10 cage $8,000
                                                     $55 per sq. ft. of bulk space
                                   ----------------------------------------------------

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

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

---------------------------------------------------------------------------------------
Carrier Termination Equp't Bays                                $700/rack
                                   ----------------------------------------------------

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

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

---------------------------------------------------------------------------------------
 Wireless Communications Tower                       40% discount of standard fees
                                   ----------------------------------------------------

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

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

---------------------------------------------------------------------------------------
       Cross Connects                             65% off standard cross-connect fees
                                   ----------------------------------------------------

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

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

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

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

CONFIDENTIAL                      Page 9 of 12                 December 23, 1999

<PAGE>   10
                               CUSTOMARY SERVICES

1.   Ample clean, reliable, redundant, battery backed AC and DC power, and
     management services of same.

2.   Ample reliable, redundant heating, cooling, air filtering and other
     customary environmental conditioning, and management services of same.

3.   Ample reliable, redundant, multi-level security systems and services,
     including but not limited to 24 x 7 camera surveillance, biometric
     scanners, secure pass key locking systems, and 24 x 7 on premises security
     personnel, and management services of same.

4.   Ample clean space in the form of partial and whole racks, caged space, and
     bulk space designed appropriately for telecommunications and server
     collocation, and management services of same.

5.   Ample reliable, redundant, modem cabling plant including but not limited to
     Car 5 UTP, COAX, and fiber optic cables and associated cross connect
     services designed appropriately for handling POTS to OC-192 to gigabit
     ethernet, and management services of same.

6.   "Smart hands" services in the form of trained telecommunications and
     networking engineers who can provide remote services that include but are
     not limited to equipment unpacking, racking, connecting, initial boot up,
     diagnostic, troubleshooting, configuration and testing services, and
     management of same.

CONFIDENTIAL                     Page 10 of 12                 December 23, 1999

<PAGE>   11
                                   EXHIBIT A

Colocation and Carrier Termination Equipment Space Agreement

CONFIDENTIAL                     Page 11 of 12                 December 23, 1999

<PAGE>   12
                                   EXHIBIT A

COLO.COM Terms and Conditions for Delivery of Service. These terms and
conditions are applicable to the COLO.COM ("COLO") Service Order Form ("Order
Form") and are incorporated in each Order Form.

1.   LICENSE. COLO hereby grants and Customer hereby accepts a limited license
     ("License") to colocate computer and communications equipment ("Equipment")
     or Carrier Termination Equipment ("Termination Equipment") in a portion of
     the Supplier controlled space ("Space") located at the premise(s)
     ("Premise" or "Premises") listed on the Order Form. COLO reserves the right
     to relocate, change or otherwise substitute the exact location of the
     Space, at any time during the Term of the License, provided that the
     substitute space is substantially similar to the original Space allotted
     and within the same geographic location and that COLO pays all reasonable
     costs of relocation and assets in the relocation. Provided that, if COLO
     moves the Carrier Equipment Termination Bay, it shall do so for all
     customers, including Customer.

     Customer hereby acknowledges and agrees that it has not been granted any
     real property interest in the Space or any of the Premises and that
     Customer has no rights as a tenant under any real property or
     landlord/tenant laws, regulations or ordinances.

     Access and Services Provided

     Where and as available to COLO, COLO will provide Customer, and its
     contractors or agents, with twenty-four hours a day, seven day a week
     access to the Space for installation, maintenance, repair, replacement or
     operation of the Equipment or Termination Equipment. For Termination
     Equipment, COLO shall provide 4 adjacent full height equipment racks in the
     primary Space it makes available to carriers for termination of their
     facilities. COLO will provide electrical power, heating, air conditioning
     and other environmental services and arrangements necessary to use of the
     Equipment in the Space. COLO shall permit Customer to cross connect to
     other facilities or Equipment of Customer or to other Customers in the
     Space and shall make available necessary facilities and access for such
     cross connections or related arrangements or shall itself provide cross
     connections and related services. COLO shall also make available access,
     Space and other facilities or arrangements necessary for Customer to
     connect its network to the Equipment or Termination Equipment, including
     from and to the building demarcation point.

2.   USE OF SPACE. Customer agrees to use the Space solely for the
     installation, maintenance, operation, and removal of Equipment or
     Termination Equipment. Nothing herein shall transfer ownership of the
     Equipment or Termination Equipment to COLO and the Equipment or
     Termination Equipment will remain the property of the Customer.

3.   CUSTOMER USE. Customer shall abide by any posted or otherwise communicated
     policies and procedures relating to COLO's facilities that are reasonable
     and customary in the industry.

4.   COLO. COLO will have the right to terminate Customer's License on sixty
     (60) days' notice if COLO loses rights to the Premises for reasons outside
     COLO's control. Provided that, COLO thereafter will make reasonable
     alternative space available and assist in any necessary transition to
     alternative Space.

5.   SERVICES & FEES. The Order Form lists the basic services and prices
     thereof ("Services") as of the order date. COLO may increase the amount
     Customer pays for Services pursuant to the Definitive Agreement.

6.   PAYMENT. Customer shall pay COLO when due for all Services ordered or
     used, including all applicable taxes, surcharges, and other government
     imposed fees. All Services shall be invoiced on a monthly basis and are
     due on or before the date appearing on the monthly billing statement. Any
     invoice not paid by the due date shall be deemed delinquent and is subject
     to interest charges accruing at a rate

                                       1
<PAGE>   13
                                   EXHIBIT A

     of 1.5% per month, Customer shall be liable for all costs of collection of
     any delinquency, including any and all collection agency fees, reasonable
     attorneys' fees, and court costs.

 7.  PAYMENT DISPUTE. Should Customer dispute any bill or any portion thereof,
     Customer shall pay the undisputed amount of the outstanding bill by the
     due date and send COLO a written explanation outlining the basis for the
     dispute. COLO shall investigate any disputed bill and within a reasonable
     time notify Customer of the outcome of such investigation. Any dispute
     that cannot be resolved by agreement shall be resolved by arbitration as
     provided in Section 16.

 8.  TERM. The term and Customer's obligation to pay COLO for the use of the
     Space shall be as provided in the Definitive Agreement or the Order Form.

 9.  CONFIDENTIALITY. Each Party, for itself, its agents, employees and
     representatives agrees that it will not divulge any confidential or
     proprietary information that it receives from the other Party. The terms
     and conditions of this contract, but not the fact this agreement has been
     entered shall be considered confidential or proprietary information under
     this paragraph. Neither Party will use the other's name in marketing
     materials without prior written consent. Customer hereby grants COLO a
     limited license to use any of its trade names and / or trademarks or
     servicemarks in any news release, marketing materials, or on COLO's web
     site announcing the agreement provided that COLO obtains Customer's prior
     written approval in each instance. All goodwill associated with Customer's
     trade names, trademarks or servicemarks will inure solely to Customer.

10.  INSURANCE. At all times during the term of the Order Form, and at each
     party's expense, COLO and Customer, and any contractors or other third
     parties representing Customer, shall maintain All Risk Property and
     casualty insurance and comprehensive general liability insurance
     (collectively "Policy"), insuring against all hazards and risks
     customarily insured against by persons colocating Equipment in buildings.
     The Policy should be written on a per-occurrence basis with blanket
     contractual liability coverage, with respect to use of the Space and
     operation of business therein, with a combined single-limit coverage of not
     less than One Million Dollars ($1,000,000) and an aggregate umbrella
     coverage of not less than an additional One Million Dollars ($1,000,000).
     A per occurrence limit of ($2,000,000) will be acceptable as well. At all
     times during the term of the Order Form, COLO requires Customer to name
     COLO and if requested by COLO in writing the landlord(s) for each Premise
     as or additional insured on the Policy. All policies shall provide that
     Customer's insures' waive all rights of subrogation against COLO.

     COLO and Customer shall maintain property insurance including EDP perils
     written on a "Special Form" basis at full replacement cost value. The
     definition of property will include data and media.

     Customer shall promptly deliver to COLO certificates of insurance issued
     by the insurance company or its authorized agent for the Policy. The
     Policy shall provide that it cannot be cancelled or modified unless COLO
     is given 30 days prior written notice of such cancellation or
     modification. Customer shall require any contractor, subcontractor,
     sublicensee entering the Space on its behalf to procure and maintain the
     same types, amounts and coverage extensions as required of Customer.

     Customer shall procure and maintain workers' compensation insurance
     complying with the law of the applicable state or states, whether or not
     such coverage is required by law, and employer's liability insurance with
     limits of no less than One Million Dollars ($1,000,000). Customer shall
     place the Policies required herein with a carrier with an AM Best rating
     of A- VIII or better. The insurance requirements set forth herein are
     independent of COLO's and Customer's indemnification and other obligations
     under and shall not be construed or interpreted in any way to restrict,
     limit,

                                       2
<PAGE>   14
                                   Exhibit A

     or modify COLO's or Customer's indemnification and other obligations, or
     to limit COLO's or Customer's liability.

11.  SERVICES PERFORMED. At times Customer may direct COLO to perform services
     that are part of COLO's service packages, installation packages, regular
     maintenance activities via service requests or under COLO's hourly service
     rates. These services typically will be associated with
     maintenance/installation type activities. COLO or where applicable, COLO's
     contractors, subcontractors etc. will not be responsible for any damage to
     Customer's equipment during such directed activities; provided COLO or
     COLO's contractors and subcontractors follow Customer's directions.

12.  INDEMNITY. To the fullest extent permitted by law, each Party shall, at
     that Party's expense, indemnify, defend and hold the other Party, its
     shareholders, officers, directors, agents, and employees harmless from and
     against all Claims, as defined below, from any cause arising out of or
     relating (directly or indirectly) to this Agreement, except claims arising
     out of or relating to the willful or intentional misconduct or negligence
     of the other Party. For purposes of this Agreement, "Claims" means any and
     all claims, causes of action (whether based on tort or contract or
     principles, law or equity, or otherwise), charges, assessments, fines, and
     penalties of any kind (including consultant and export expenses, court
     costs, and reasonable attorneys' fees). This indemnification extends to
     and includes Claims for: (i) injury to any persons (including death at any
     time resulting from that injury); (ii) loss of, injury or damage to, or
     destruction of real or personal property (including all loss of use
     resulting from that loss, injury, damage, or destruction of the Space or
     Premises); and (iii) all direct economic losses. The indemnification may
     not be construed or interpreted as in any way restricting, limiting, or
     modifying COLO's or Customer's insurance or other obligations under the
     Order Form and is independent of COLO's and Customer's insurance
     obligations. The provisions of this paragraph shall survive the expiration
     or earlier termination of the Order Form until all Claims involving any of
     the Indemnified matters are fully, finally, and absolutely barred by the
     applicable statutes of limitation.

13.  DISCLAIMER OF WARRANTY. COLO represents that it has full rights and legal
     authority to grant the rights herein and that COLO is not aware of and
     will correct any latent defects. Otherwise, Customer accepts the Space and
     services on an 'as is' basis at its own risk. Unless specifically stated
     herein, COLO makes no warranties, express or implied, as to the Space,
     Premises, or services. COLO specifically disclaims any and all express or
     implied warranties, including without limitation any warranties of
     merchantability or fitness for a particular purpose.

14.  DEFAULT. In the event that Customer fails to perform any material
     obligation under the Order Form which has not been cured within thirty
     (30) days of receiving a written notice of default, COLO shall have the
     right to immediately terminate the License; provided however that in the
     event that any action or non-action threatens or causes harm to any Space
     or Premises, COLO shall have the right to immediately request cessation of
     the action or that Customer take immediate curative action.

15.  TERMINATION. Upon expiration or earlier termination of the License; (1)
     COLO will cease providing Services under the Order Form, or any applicable
     License; (2) any and all payment obligations of Customer then existing
     under this Order Form will become due and payable immediately; (3)
     Customer shall quit and peacefully surrender that portion of the
     applicable Space it uses to COLO and remove all Equipment or Termination
     Equipment from all affected Space, at its expense; (4) Customer, at its
     expense, shall repair, replace, or compensate COLO for any damage to the
     Space or Premises resulting from the removal of the Equipment or
     Termination Equipment within thirty (30) days of receiving notice of any
     such damage; (5) within forty-five (45) days after the expiration or
     earlier termination date of the Order Form or the appropriate License, if
     Customer has not removed the Equipment or Termination Equipment from the
     appropriate Premise(s) and COLO has provided ten (10)

                                       3
<PAGE>   15
                                   EXHIBIT A

     days written notice thereof to Customer, Customer shall be deemed to have
     abandoned its claim of ownership to the Equipment or Termination Equipment
     and to have conveyed all of its right, title, and interest to the
     Equipment or Termination Equipment to COLO without set-off or any other
     credit of any amount that may be owed to COLO by Customer, and (6) each
     party shall return all Confidential Information of the other Party in its
     possession and will not make or retain any copies of such Confidential
     Information except as required to comply with any applicable legal or
     accounting record keeping requirement.

16.  ARBITRATION. Any disputes arising in connection with the Order Form or this
     License that cannot be amicably settled by direct negotiations will be
     submitted to final and binding arbitration in accordance with the
     then-prevailing commercial rules of the American Arbitration Association.
     The arbitration will be held in San Francisco, California. Unless
     otherwise agreed to by the Parties, one (1) arbitrator shall hear the
     matter. The arbitrator's decision shall be based upon the Terms and
     Conditions, the Definitive Agreement, Order Form and applicable law giving
     full force and legal effect to the insurance, indemnity, disclaimer, and
     limitation of liability provisions. Any court with competent jurisdiction
     may enter judgment upon the award rendered by the arbitrator.
     Notwithstanding the foregoing, nothing contained herein shall prohibit
     either Party from initiating judicial proceedings for the limited purpose
     of seeking an unlawful detention order or seeking other provisional or
     equitable remedies. Any such judicial proceedings shall be heard by the
     state or federal court located in the county where the applicable Space,
     Premise, or Equipment is located. In all other respects this Section shall
     govern resolution of any controversy or claim arising in connection with
     the Order Form.

17.  FORCE MAJEURE. Notwithstanding anything to the contrary contained herein,
     neither party shall be liable for any loss or damage, or deemed to be in
     breach of the Order Form due to a failure to perform, wholly or in part,
     if such nonperformance is due to causes beyond that Party's control,
     including acts of God, fire, explosion, earthquake, hurricane, tornado,
     wind, flood, storm or other natural occurrences; vandalism; third party
     theft; computer, voice mail, e-mail, or other telecommunications system
     failure; any law, order, regulation, direction, action or lawful demand of
     any Federal, state, local or foreign governments having jurisdiction or of
     any department, agency, commission, court, bureau, corporation or other
     instrumentality of any one or more such governments, or of any civil or
     military authority; national emergency; insurrection; riot; war; strike,
     lockout, work stoppage or other such labor difficulty.

18.  ASSIGNMENT. The Order Form shall not be assigned or delegated without
     first obtaining the prior written consent of the other Party, which
     consent shall not be unreasonably withheld. Any purported assignment or
     delegation without the required consent shall be null and void and of no
     legal force or effect.

19.  GOVERNING LAW. The Order Form shall be governed by and interpreted in
     accordance with the laws of the State of California. In the event of a
     dispute or litigation regarding the Order Form, the prevailing party shall
     be entitled to receive reasonable attorneys fees and costs.

20.  NO WAIVER. The failure of either Party at any time to enforce any right or
     remedy available to it under the Order Form with respect to any breach or
     failure shall not be construed to be a waiver of such right or remedy with
     respect to any other breach of failure.

21.  LIABILITY. Except for the indemnification provided in Section 12, the
     liability of COLO for damages arising out of the furnishing of Space or
     services or the failure to provide Space or services, including but not
     limited to mistakes, omissions, interruptions, delays, tortious conduct,
     representations, errors, or other defects, whether by commission or
     omission, shall be limited to an amount equal to the fees for the use of
     the applicable Space. Except for the indemnification provided in Section
     12, the liability of NEXTLINK for damages under or arising

                                       4
<PAGE>   16

                                   Exhibit A

      from this Agreement shall be limited to an amount equal to the fees for
      use of the applicable Space.

22.   SURVIVAL. The obligations of confidentiality and indemnification shall
      survive the termination of any applicable Order Form.

23.   ENTIRE UNDERSTANDING. The Order Form, these Terms and Conditions for
      Delivery of Service and the Definitive Agreement constitute the entire
      understanding of the parties related to the subject matter hereof. The
      Definitive Agreement shall prevail over these Terms and Conditions or the
      Order Form and the Terms and Conditions shall prevail over the Order Form.

                                       5

<PAGE>   17

                                   EXHIBIT B

                             TOWER RIGHTS AGREEMENT

CONFIDENTIAL                     Page 12 of 12                 December 23, 1999

<PAGE>   18
                                TOWER AGREEMENT

This Tower Agreement ("Agreement") is made as of this _______ day of __________,
20__ ("Effective Date"), between COLO.COM, a California corporation ("COLO"),
and NEXTLINK Communications, Inc. a Delaware corporation ("NEXTLINK").

1.  LICENSE. COLO hereby grants and NEXTLINK hereby accepts a limited license to
    install, operate and maintain wireless telecommunications equipment and
    related equipment ("Equipment") on COLO's antenna tower ("Tower") on the
    roof of the building  located at _____________________________ ("Building").
    NEXTLINK shall also have the right to install all reasonable wiring related
    to the Equipment and to connect the same to NEXTLINK's equipment space, its
    customers or other carriers in the Building, provided that COLO has access
    to and the right to use risers or other functionally similar portions of the
    Building. NEXTLINK hereby acknowledges and agrees that it has not been
    granted any real property interest in the Tower or any of the Building and
    that NEXTLINK has no rights under this Agreement as a tenant under any real
    property or landlord/tenant laws, regulations or ordinances. COLO shall make
    the full rights hereunder available to NEXTLINK upon the Effective Date.

2.  ACCESS. Where and as available to COLO, COLO will provide NEXTLINK, and its
    contractors or agents, with twenty-four hours a day, seven day a week access
    to the Tower for installation, maintenance, repair, replacement or operation
    of the Equipment. COLO will provide electrical power for the Equipment on
    the Tower.

3.  PERMITS AND COMPLIANCE WITH LAWS. NEXTLINK shall be solely responsible for
    obtaining any permits and licenses required to install and operate the
    Equipment. COLO agrees to reasonably cooperate with NEXTLINK in executing
    any documents or applications required for NEXTLINK to obtain such permits
    and licenses needed for NEXTLINK to exercise its rights under this
    Agreement. NEXTLINK shall comply with all applicable laws with respect to
    its installation and operation of the Equipment.

4.  USE OF SPACE. NEXTLINK agrees to use the Tower and related access solely for
    the installation, maintenance, operation, and removal of Equipment. Nothing
    herein shall transfer ownership of the Equipment to COLO and the Equipment
    will remain the property of the NEXTLINK. NEXTLINK shall abide by any posted
    or otherwise communicated policies and procedures relating to COLO's Tower
    that are reasonable and customary in the industry.

5.  LOSS OF COLO'S RIGHTS TO TOWER. COLO will have the right to terminate this
    Agreement on sixty (60) days' notice if COLO loses rights to the Tower for
    reasons outside COLO's control; provided, however, that COLO thereafter will
    assist in any necessary transition to an alternative tower, if reasonable
    alternative antenna towers are available.

6.  FEE AND PAYMENT. NEXTLINK shall pay COLO $___________ per month (pro rated
    for partial months), commencing 20 days after the Effective Date. COLO shall
    bill NEXTLINK on a monthly basis, and payment shall be due on or before the
    date appearing on the monthly billing statement. Any invoice not paid by the
    due date shall be deemed delinquent and is subject to interest charges
    accruing at a rate of 1.5% per month. NEXTLINK shall be liable for all costs
    of collection of any delinquency, including any and all collection agency
    fees, reasonable attorneys' fees, and court costs. NEXTLINK shall pay all
    taxes and other fees or charges attributable to the Equipment.

7.  TERM. The term of this Agreement shall be ___ years from the Effective Date
    (plus any partial calendar month in which the Effective Date falls).
    NEXTLINK shall have the option of extending this Agreement, by giving COLO
    90 days written notice before the expiration of the then-current term, for
    an additional ____ term(s) of ____ years upon the same terms and conditions
    as contained herein.

                                      1

<PAGE>   19
8.   INSURANCE. At all times during the term of the Agreement, and at each
     party's expense, COLO and NEXTLINK, and any contractors or other third
     parties representing NEXTLINK or COLO, shall maintain All Risk Property
     and casualty insurance and comprehensive general liability insurance
     (collectively "Policy"), insuring against all hazards and risks
     customarily insured against by persons installing Equipment on antenna
     towers. The Policy should be written on a per-occurrence basis with
     blanket contractual liability coverage, with respect to use of the Tower,
     with a combined single-limit coverage of not less than One Million Dollars
     ($1,000,000) and an aggregate umbrella coverage of not less than an
     additional One Million dollars ($1,000,000). At all times during the term
     of the Agreement, NEXTLINK shall name COLO and, if requested by COLO in
     writing, the landlord(s) for the Building, as additional Insured on the
     Policy. COLO and NEXTLINK shall also maintain property insurance including
     EDP perils written on a "Special Form" basis at full replacement cost
     value. The definition of property will include data and media.

     NEXTLINK shall promptly deliver to COLO certificates of insurance issued
     by the insurance company or its authorized agent for the Policy. The
     Policy shall provide that it cannot be cancelled or modified unless COLO
     is given 30 days prior written notice of such cancellation or
     modification. NEXTLINK shall require any contractor or subcontractor
     working on the Tower on its behalf to procure and maintain the same types,
     amounts and coverage extensions as required of NEXTLINK.

     NEXTLINK shall procure and maintain workers' compensation insurance
     complying with the law of the applicable state or states, whether or not
     such coverage is required by law, and employer's liability insurance with
     limits of no less than One Million Dollars ($1,000,000). NEXTLINK shall
     place the Policies required herein with a carrier with an AM Best rating
     of A-VIII or better. The insurance requirements set forth herein are
     independent of COLO's and NEXTLINK's indemnification and other obligations
     under and shall not be construed or interpreted in any way to restrict,
     limit, or modify COLO's or NEXTLINK's indemnification and other
     obligations, or to limit COLO's or NEXTLINK's liability under the
     Agreement.

9.   INDEMNITY. To the fullest extent permitted by law, COLO and NEXTLINK shall
     each, at his expense, indemnify, defend and hold the other, its
     shareholders, officers, directors, agents, and employees harmless from and
     against all Claims, as defined below, from any cause arising out of or
     relating (directly or indirectly) to this Agreement, except claims arising
     out of or relating to the willful or intentional misconduct or negligence
     of the other party. For purposes of this Agreement, "Claims" means any and
     all claims, causes of action (whether based on tort or contract law
     principles, law or equity, or otherwise), charges, assessments, fines, and
     penalties of any kind (including consultant and expert expenses, court
     costs, and reasonable attorneys' fees). This indemnification extends to
     and includes Claims for: (i) injury to any persons (including death at any
     time resulting from that injury); (ii) loss of, injury or damage to, or
     destruction of real or personal property (including all loss of use
     resulting from that loss, injury, damage, or destruction of the Tower or
     Premises); and (iii) all direct economic losses. This indemnification may
     not be construed or interpreted as in any way restricting, limiting, or
     modifying COLO's or NEXTLINK's insurance or other obligations under this
     Agreement and is independent of COLO's and NEXTLINK's insurance
     obligations. The provisions of this paragraph shall survive the expiration
     or earlier termination of this Agreement and all Claims involving any of
     the indemnified matters are fully, finally, and absolutely barred by the
     applicable statutes of limitation.

10.  DISCLAIMER OF WARRANTY. COLO represents that it has full rights and legal
     authority to grant the rights herein and that COLO is not aware of and
     will promptly correct any latent defects. Otherwise, NEXTLINK accepts the
     Tower on an 'as is' basis at its own risk. Unless specifically stated
     herein or in the Definitive Agreement between the parties, COLO makes no
     warranties, express or implied, as to the Tower or the Building. COLO
     specifically disclaims any and all express or implied warranties,
     including without limitation any warranties of merchantability or fitness
     for a particular purpose.

                                       2
<PAGE>   20
11.  DEFAULT. In the event that NEXTLINK fails to perform any material
     obligation under this Agreement that is not cured within thirty (30) days
     of receiving a written notice of default, COLO shall have the right to
     immediately terminate the Agreement; provided, however, that in the event
     that any action or non-action of NEXTLINK threatens to or causes harm to
     the Tower or the Building, COLO shall have the right to immediately request
     cessation of the action or that NEXTLINK take immediate curative action.

12.  TERMINATION. Upon expiration or earlier termination of the Agreement: (1)
     any and all NEXTLINK's payment obligations then accrued under this
     Agreement will become due and payable immediately; (2) NEXTLINK shall quit
     and peacefully surrender that portion of the Tower it uses to COLO and
     remove all Equipment from the Tower, at NEXTLINK's expense; (3) NEXTLINK,
     at its expense, shall repair, replace, or compensate COLO for any damage to
     the Tower or Building resulting from the removal of the Equipment within 30
     days of receiving notice of any such damage; (4) within 45 days after the
     expiration or earlier termination date of the Agreement, if NEXTLINK has
     not removed the Equipment from the Tower, NEXTLINK shall be deemed to have
     abandoned its claim of ownership to the Equipment and to have conveyed all
     of its right, title, and interest to the Equipment to COLO without setoff
     or any other credit of any amount that may be owed to COLO by NEXTLINK;
     provided, however, that COLO shall have given NEXTLINK at least 10 days
     prior written notice of the end of the 45 day period and (5) each party
     shall return all confidential or proprietary information of the other party
     in its possession and will not make or retain any copies of such
     confidential information except as required to comply with any applicable
     legal or accounting record keeping requirement.

13.  DISPUTE RESOLUTION. Any dispute arising between COLO and NEXTLINK under
     this Agreement shall be governed by the dispute resolution provision in the
     Definitive Agreement between the parties.

14.  FORCE MAJEURE. Notwithstanding anything to the contrary contained here,
     neither party shall be liable for any loss or damage, or deemed to be in
     breach of the Agreement due to a failure to perform, wholly or in part, if
     such nonperformance is due to causes beyond that party's control, including
     acts of God, fire, explosion, earthquake, hurricane, tornado, wind, flood,
     storm or other natural occurrences; vandalism; third party that computer,
     voice mail, e-mail, or other telecommunications system failure; any law,
     order, regulation, direction, action or lawful demand of any Federal,
     state, local or foreign governments having jurisdiction or of any
     department, agency, commission, court, bureau, corporation or other
     instrumentality of any one or more such governments, or of any civil or
     military authority, national emergency; insurrection; riot; war; strike,
     lockout, work stoppage or other such labor difficulty.

15.  ASSIGNMENT AND AMENDMENT. Assignment and amendment of this Agreement shall
     be governed by the assignment and amendment provisions in the Definitive
     Amendment between the parties.

16.  GOVERNING LAW. The Agreement shall be governed by and interpreted in
     accordance with the laws of the State of California. Except as otherwise
     provided in Paragraph 13, venue shall be in the state of California. In
     the event of a dispute or litigation regarding the Agreement, the
     prevailing party shall be entitled to receive reasonable attorney's fees
     and costs.

17.  LIABILITY. Except for the indemnification provided in Paragraph 9, the
     liability of COLO for damages arising out of the furnishing or failure to
     furnish the Tower and other obligations under the Agreement, including but
     not limited to mistakes, omissions, interruptions, delays, tortious
     conduct, representations, errors, or other defects, whether by commission
     or omission, shall be limited to an amount equal to the fees for the use
     of the Tower. Except for the indemnification provided in Paragraph 9, the
     liability of NEXTLINK for damages under or arising from this Agreement
     shall be limited to an amount equal to the fees for use of the Tower.

                                       3

<PAGE>   21
18. NOTICES. Any notice required or permitted to be given hereunder must be in
    writing and may made by personal delivery (including by overnight service),
    or by registered or certified mail, postage prepaid, return receipt
    requested, as provided below:

          COLO:

          NEXTLINK:

               With a copy to:  NEXTLINK Communications, Inc.
                                500 -- 108th Avenue, Suite 2200
                                Bellevue, WA 98004
                                Attn: General Counsel

    Either party may, by written notice to the other, specify a different
    address for notice purposes. Notices shall be deemed received when delivered
    or when delivery is refused.

19. ENTIRE UNDERSTANDING. The Agreement and the Definitive Agreement between the
    parties constitute the entire understanding of the parties related to the
    subject matter hereof. In the event of an inconsistency, the Definitive
    Agreement shall prevail over this Agreement.

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

COLO.COM

By: ____________________________________

Title: _________________________________

Date: __________________________________

NEXTLINK Communications, Inc.

By: ____________________________________

Title: _________________________________

Date: __________________________________

                                       4

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00010-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00010-of-00352.parquet"}]]