Document:

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                                                                    Exhibit 10.1

                               NET BUILDING LEASE

                                     BETWEEN

                       PERIMETER CENTER INVESTORS, L.L.C.
                                  ("Landlord")

                                       AND

                     NET2000 COMMUNICATIONS REAL ESTATE, INC.
                                   ("Tenant")
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                                LEASE AGREEMENT

         THIS LEASE AGREEMENT (the "Lease"), made and entered into this 11th day
of April, 2000, by and between PERIMETER CENTER INVESTORS, L.L.C., a Georgia
limited liability company, and DOUBLE FEATURE, L.L.C., a Georgia limited
liability company (collectively, the "Landlord"), and NET2000 COMMUNICATIONS
REAL ESTATE, INC., a Delaware corporation (the "Tenant"):

                              W I T N E S S E T H:

         WHEREAS, Landlord desires to demise, lease and rent unto the Tenant,
and Tenant desires to rent and lease from Landlord, that certain real property
("Land") located at 48 Perimeter Center East, Atlanta, Georgia more particularly
described in Exhibit A hereto, together with the building ("Building") and all
improvements thereon and appurtenant rights thereto including, without
limitation, parking areas, easements, declarations and rights of way (together
with the Land and the Building, the "Premises"), all of which are shown on the
plan attached hereto as Exhibit B.

         WHEREAS, the Building is a two (2) story building containing
approximately twenty-three thousand three hundred thirty-four (23,334) rentable
square feet, and includes without limitation, all heating, venting, air
conditioning, mechanical, electrical, elevator and plumbing systems, roofs,
walls and foundations and fixtures, and the Premises shall include an
approximately ninety (90) space parking lot;

         NOW, THEREFORE, for and in consideration of the mutual covenants,
promises and agreements herein contained, Landlord does hereby demise, lease and
rent unto Tenant and Tenant does hereby rent and lease from Landlord the
Premises, under and pursuant to the following terms and conditions:

         1. Term. The term ("Term") of the Lease shall be ten (10) years
beginning on the later of (i) the date Landlord delivers possession of the
Premises to Tenant in the condition required herein or (ii) April 1, 2000 (the
"Commencement Date") and ending at midnight on the last day of the calendar
month in which the tenth (10th) anniversary of the Rent Commencement Date (as
such term is hereinafter defined) occurs (as the same may be extended, the
"Termination Date"), unless renewed as hereinafter provided. "Lease Year" shall
mean the twelve (12) month period beginning on the Rent Commencement Date and
each twelve (12) month period thereafter, provided however, that if the Rent
Commencement Date does not occur on the first day of a month, then the first
Lease Year shall expire on the last day of the month in which the one-year
anniversary of the Rent Commencement Date occurs.

         2. Rent. As of the Rent Commencement Date (hereinafter defined), Tenant
agrees to pay as an annual base rent ("Rent") the amount set forth in the table
attached hereto as Schedule I and made a part hereof by this reference. Tenant
shall pay the Rent in monthly installments, in advance on the first day of each
calendar month for each and every month during the Term, any such monthly
installment to be prorated for any partial calendar month in which the Rent
Commencement

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Date or Termination Date shall occur. All amounts (unless otherwise provided
herein) other than the Rent owed by Tenant to Landlord hereunder shall be deemed
additional rent ("Additional Rent").

         The installments of Rent and Additional Rent for any initial partial
calendar month shall be prorated based on actual days elapsed, and shall be paid
in advance on the Rent Commencement Date.

         Except as expressly provided to the contrary in this Lease,
installments of Rent and Additional Rent shall be payable without notice,
demand, reduction, set off, or other defense. Installments of Rent and
Additional Rent and payments of other sums owing to Landlord pursuant to this
Lease shall be made to Landlord located at 5755 Dupree Drive, Suite 110,
Atlanta, Georgia 30327, or at whatever other account or address that Landlord
may designate from time to time by written notice delivered to Tenant not less
than thirty (30) days in advance of the effective date of any such change.

         If any installment of Rent or Additional Rent, or any other sum due and
payable pursuant to this Lease, remains unpaid for more than five (5) days after
the date due, Tenant shall pay Landlord a late payment charge equal to the
greater of (i) Fifty and No/100 Dollars ($50.00), or (ii) five percent (5%) of
the unpaid installment or other payment. The late payment charge is intended to
compensate Landlord for administrative expenses associated with responding to
late payment, and shall not be considered liquidated damages or interest. All
Rent, Additional Rent and other sums of whatever nature owed by Tenant to
Landlord under this Lease that remain unpaid for more than ten (10) days shall
bear interest from the date due until paid at the lesser of (iii) five percent
(5%) in excess of the prime or general reference rate of interest of Chase
Manhattan Bank of New York (or its successors) in effect from time to time, or
(iv) the maximum interest rate per annum allowed by law.

         The "Rent Commencement Date" shall be the later of (i) August 1, 2000
or (ii) the date on which Landlord delivers possession of the First Floor Space
(as defined in Section 5) to Tenant free and clear of any leases, occupancy or
related agreements or tenancies, broom clean and free of all personal property
and equipment.

         Except as otherwise provided in this Lease, it is the intention of the
parties that Landlord shall receive the Rent, Additional Rent, and all other
sums payable to Landlord by Tenant under this Lease free of all taxes, expenses,
charges, damages and deductions of any nature whatsoever and Tenant covenants
and agrees to pay all sums which except for this Lease would have been
chargeable against the Premises and payable by Landlord. Tenant shall, however,
be under no obligation to pay principal or interest on any mortgage on the fee
of the Premises, any franchise or income tax payable by Landlord or any other
tax is imposed upon or measured by Landlord's income or profits, or any gift,
inheritance, transfer, estate, or succession tax by reason of any present or
future law which may be enacted during the Term.

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         Notwithstanding anything to the contrary contained in this Section 2,
for the first four (4) months after the Rent Commencement Date, Tenant shall pay
Rent at one-half (1/2) the monthly rate set forth in the table above.

         Upon the execution of this Lease, Tenant shall deliver to Landlord the
first and last month's Rent hereunder, together with the monthly amounts
estimated by Landlord totaling S2,510.00 relative to Tenant's obligations
hereunder for reimbursement to Landlord of Real Estate Taxes and Landlord's
Insurance Costs for the Premises (i.e., $26,038.45 and $31,249.71,
respectively).

         3. Renewals. Provided Tenant is not then in default under this Lease
(beyond any applicable notice and cure periods), Tenant shall have the right and
option to renew this Lease for two (2) additional periods of five (5) years
each, next immediately ensuing after the expiration of the initial Term of
this Lease and the subsequent renewal period by notifying Landlord in writing
not less than six (6) months before the expiration of the immediately preceding
initial Term or subsequent renewal Term of this Lease. In the event that Tenant
so elects to extend this Lease, then, for such extended period of the Term, all
of the terms, covenants and conditions of this Lease shall be in full force and
effect during such extended period of the Term hereof.

         4. Use of Premises, Compliance with Legal Requirements. Tenant may use
and occupy the Premises during the Term for the operation of a
telecommunications switch site (including collocation with third party
telecommunications providers) and related office and operations facilities, and
for any other lawful purpose. Tenant may install, use and maintain in the
Premises cabinets, racks, switches, risers, feeders, conduits and such other
telecommunications facilities and equipment necessary or desired by Tenant for
such purposes. Tenant shall, at its sole cost and expense, comply with all laws,
ordinances and regulations of any governmental authority relating to Tenant's
use or occupancy of the Premises, with the requirements of insurance
underwriters or rating bureaus applicable to the Property.

         5. Condition of Premises. Tenant accepts the Premises in "as is"
condition, subject only to Landlord's maintenance and repair obligations set
forth herein, free of all leases, occupancy or related agreements or tenancies
other than a lease (the "First Floor Lease") for space on the first floor of the
Building (the "First Floor Space"), which First Floor Lease expires on July 31,
2000. Landlord does hereby agree to use all commercially reasonable efforts
(including the initiation of dispossessory proceedings, if required) to cause
the occupants of the First Floor Space to vacate the premises subject to the
First Floor Lease as soon after the expiration of the term of the First Floor
Lease as is possible. For the period beginning on the Commencement Date and
continuing for so long as the tenant under the First Floor Lease shall remain in
possession of any portion of the First Floor Space, Landlord shall promptly pay
to Tenant, on or before the tenth (10th) calendar day of each calendar month,
the sum of $5,712.50, prorated for any partial month. Notwithstanding the
foregoing, in the event that the activities of Tenant in and around the Premises
shall give rise to a claim by the tenant under the First Floor Lease that its
rights under the First Floor Lease (including, without limitation, the right to
quiet enjoyment of its demised premises) shall have been breached or violated,
and as a result thereof, said tenant under the First Floor Lease shall refuse to
pay all or any portion of the rent payable with respect to the period commencing
on the Commencement Date

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and ending on the Rent Commencement Date; then in such event, Landlord's
obligation to pay to Tenant the sum of $5,712.50 per month as described
immediately hereinabove shall be extinguished and eliminated, and instead,
Landlord shall promptly pay, within five (5) calendar days after receipt, all
rents actually collected by Landlord under said First Floor Lease, together with
the security deposit (or last month's rent) held by Landlord (subject, however,
to any claims of said tenant). Subject to the foregoing, in the event Landlord
shall fail to pay such amount when due, Tenant shall have the right to offset or
credit such amount against any Rent, Additional Rent or other sum payable to
Landlord by Tenant under this Lease.

         6. Assignment/Subletting. The Tenant shall not assign this Lease, or
sublet the Premises, or any part thereof, without Landlord's prior written
consent which consent shall not be unreasonably withheld or delayed. Prior to
any sublease or assignment, Tenant shall first notify Landlord in writing of its
election to sublease all or a portion of the Premises or to assign this Lease or
any interest thereunder. At any time within fifteen (15) days after said notice,
Landlord shall notify Tenant that it consents or refuses to consent to the
sublease or assignment. A failure by Landlord to respond within such
fifteen (15) day period shall be deemed to be a consent.

         Any assignment or subletting shall not release Tenant of its liability
under this Lease nor permit any subsequent assignment, subletting or other
prohibited act, unless specifically provided in such consent.

         Notwithstanding the foregoing, no consent of Landlord is required for
Tenant to assign, sublet or otherwise transfer (by operation of law or
otherwise) this Lease or any of its rights hereunder: (a) to any person,
corporation, partnership or other entity which acquires all or substantially all
of the business or assets of Tenant or stock in Tenant, or (b) to any person,
corporation, partnership or other entity which controls, is controlled by or is
under common control with Tenant, or (c) in connection with any merger,
consolidation or reorganization of Tenant with or into another entity. In each
of such events (except only where, as a result of a merger, consolidation or
reorganization of Tenant, Tenant ceases to exist as a separate and distinct
legal entity), Tenant shall remain liable on this Lease for the entire Term
hereof (including any extension periods), and Tenant shall in no way whatsoever
be relieved of any liability for performance of any of the terms, conditions,
covenants and agreements contained herein to be performed by Tenant upon such
assignment, transfer or conveyance. Notwithstanding the foregoing, in the event
that as a result of a proposed merger, consolidation or reorganization of
Tenant, it is contemplated that Tenant shall cease to exist as a separate and
distinct legal entity, then in such event Tenant's successor or surviving entity
shall, as a precondition to the assignment of Tenant's rights in and to the
Lease in connection with any such merger, consolidation or reorganization of
Tenant, (i) assume, in a writing reasonably acceptable to Landlord, all of the
obligations of Tenant under the terms of this Lease, (ii) cause Net2000
Communications Group, Inc., if it shall be a surviving entity, and if not,
another entity with a net worth not less than the net worth of said Net2000
Communications Group, Inc. to guaranty the obligations of said successor or
surviving entity under the Lease; and upon the receipt by Landlord of such
assumption agreement and such guaranty, the transferring tenant shall be
relieved of any further liability for the performance of any of the terms,
conditions, covenants and

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agreements contained herein to be performed by Tenant from and after the date of
such merger, consolidation or reorganization.

         Nothing contained herein shall be deemed to prohibit, limit or restrict
Tenant from, or require Landlord's consent to, collocating telecommunications
equipment at the Premises or from licensing or subletting cabinets, racks,
risers, feeders, conduits, chases or other equipment.

         Landlord hereby consents to a collateral assignment or mortgage of this
Lease by Tenant to a lender of Tenant's choice, provided, however, Tenant shall
be and remain liable for the performance of this Lease.

         7. Tenant to Pay Taxes, Utilities and Operating Expenses.

         (a) In addition to the Rent described in Section 2 hereinabove, Tenant
shall, commencing with the Commencement Date and thereafter during the Term
hereof, be responsible for all "Real Estate Taxes" (as hereinafter defined)
imposed upon the Premises; and in this regard Tenant does hereby agree to pay to
Landlord, as Additional Rent, the Real Estate Taxes in the amounts and manner
described hereinbelow.

         For the purposes of this Lease, the phrase "Real Estate Taxes" shall
mean all ad valorem real estate taxes and currently due installments of
assessments and all other governmental levies made with respect to real property
and payable by owners of such property which are due and payable for any tax
year falling in whole or in part within the Term. In the event the present
system of real estate taxation changes so that a new or different tax in
assessed against the Premises in lieu of or in addition to the existing real
estate taxes, Tenant shall also pay such new or additional real estate taxes,
provided that (i) such taxes are unique to owners of real property and are based
on such ownership (including, without limitation, a rents tax) and (ii) Tenant
shall pay no more than would be payable if the Premises was the only property
owned by Landlord. Notwithstanding the foregoing, Real Estate Taxes shall not
include any income, capital stock, gift, estate, transfer or inheritance tax.
All special assessments shall be included in Real Estate Taxes as if paid in the
maximum number of installments permissible. Real Estate Taxes on any partial tax
year at the beginning or end of the Term shall be prorated on the basis of the
number of days within the Term.

         Landlord shall from time to time estimate the Real Estate Taxes on a
"Lease Year" basis, and Tenant shall pay one-twelfth (1/12th) of such estimated
amount in advance in equal monthly installments, together with Tenant's monthly
payments of Rent (provided, however, that with respect to installments due for
the period prior to the Rent Commencement Date, said monthly installments shall
be due and payable in the same manner as is described in Section 2. hereinabove
with respect to the payment of Rent). Within ninety (90) days following each
Lease Year, Landlord shall calculate the actual amount of Real Estate Taxes and
Landlord shall furnish Tenant copies of all tax bills. In the event the
aggregate of Tenant's installments during any such period shall be less than the
actual amount of the Real Estate Taxes, such deficiency shall be paid to
Landlord within thirty (30) days after demand therefor. In the event the
aggregate of Tenant's installments during any such period shall exceed the
amount of Real Estate Taxes, such excess shall be a credit against subsequently
occurring installments of estimated Real Estate Taxes due from Tenant until such

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credit is exhausted and if said installments of estimated Real Estate Taxes
subsequently owed by Tenant are insufficient to absorb Tenant's overpayment,
Landlord shall refund to Tenant the unabsorbed portion of the overpayment if no
Event of Default on the part Tenant is then in existence. For any period within
the Term, which is less than twelve (12) months, the Real Estate Taxes shall be
appropriately prorated. Tenant will be allowed to pay taxes in the event
Landlord does not pay them.

         Subject to adjustment as contemplated above, Tenant shall, commencing
on the Commencement Date, pay Landlord in advance on the first (1st) day of each
calendar month a monthly installment of Landlord's initial estimate of the Real
Estate Taxes in an amount equal to $2,300.00.

         Tenant may contest the amount or validity of any Real Estate Taxes by
appropriate proceedings. However, Tenant shall promptly pay all such Real Estate
Taxes unless such proceedings shall operate to prevent or stay the collection of
the Real Estate Taxes so contested. Landlord, at Tenant's sole expense, shall
join in any such contest if any Law shall so require.

         (b) In addition to the Rent described in Section 2. hereinabove, Tenant
shall, commencing on the Commencement Date and continuing thereafter for the
entire Term hereof, pay for all utilities and other services necessary in the
operation of the Premises, including, but not limited to, gas, fuel oil,
electrical, telephone, water, sanitary sewer and other utility charges,
janitorial services (if Tenant shall contract for such services), grounds
maintenance and Building maintenance (except as otherwise provided for in
Section 18. hereinbelow).

         (c) All sums (other than the Rent) which may be due and payable to
Landlord under this Lease shall be deemed to be Additional Rent hereunder and in
the event that Rent shall be prorated or shall abate pursuant to the terms of
this Lease then such Additional Rent shall be prorated or abate to the same
extent and in the same manner, unless otherwise specifically provided for in
this Lease.

         8. Insurance. In addition to the Rent described in Section 2
hereinabove, commencing with the Commencement Date and continuing thereafter
during the entire Term hereof, Tenant shall pay to Landlord, as Additional Rent
and in the manner described hereinbelow, an amount equal to Landlord's Insurance
Costs.

         For the purpose of this Lease, "Landlord's Insurance Costs" shall mean
any and all premiums for the insurance required to be obtained and maintained by
Landlord in accordance with the provisions of Section 16. hereinbelow.

         Landlord shall from time to time estimate the amount of Landlord's
Insurance Costs on a "Lease Year" basis, and Tenant shall pay one-twelfth (1/12)
of such estimate in advance in equal installments, together with Tenant's
monthly payments of Rent (provided, however, that with respect to installments
due for the period prior to the Rent Commencement Date, said monthly
installments shall be due and payable in the same manner as is described in
Section 2. hereinabove with respect to the payment of Rent). Within ninety (90)
days following each Lease Year, Landlord will furnish to Tenant a statement
showing in reasonable detail the amount of Landlord's Insurance Costs for the

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preceding period and the actual amount due by Tenant. In the event the aggregate
of Tenant's installments during any such period shall be less than the actual
amount due by Tenant of Landlord's Insurance Costs, such deficiency shall be
paid to Landlord within thirty (30) days after demand therefore. In the event
the aggregate of Tenant's installments during any such period shall exceed the
actual amount of Landlord's Insurance Costs, such excess shall be a credit
against subsequently occurring payments by Tenant of Landlord's Insurance Costs
until such credit is exhausted, and if the amount of Landlord's Insurance Costs
subsequently owned by Tenant is insufficient to absorb Tenant's overpayment,
Landlord shall refund to Tenant the unabsorbed portion of such overpayment if no
Event of Default on the part of Tenant is then in existence. For any period
within the Term, which is less than a full year, amount due by Tenant of
Landlord's Insurance Costs shall be appropriately prorated.

         Subject to adjustment contemplated above, Tenant shall, commencing on
the Commencement Date, pay Landlord in advance on the first (1st) day of each
calendar month a monthly installment of Landlord's initial estimate of
Landlord's Insurance Costs in an amount equal to $210.00.

         Tenant further agrees to pay on demand any increase in premiums that
may be charged on insurance carried by Landlord resulting from Tenant's use or
occupancy of the Premises.

         9. Alterations. Tenant, at its own expense, may from time to time
during the term of this Lease make any interior alterations, additions and
improvements in and to the Building which it may deem necessary or desirable and
which do not adversely affect the structural integrity thereof, but it shall
make them in good workmanlike manner and in accordance with all valid
requirements of municipal or other governmental authorities. Tenant shall not
make any structural alterations, additions, modifications or improvements to the
Building or the Premises other than the Tenant Alterations (as such term is
hereinafter defined) (such structural alterations, additions, modifications and
improvements [excluding the Tenant Alterations], being hereinafter referred to,
collectively, as "Structural Alterations"), without the prior written consent of
Landlord (which consent shall not be unreasonably withheld or delayed). In the
event that Tenant shall desire to make any such Structural Alterations to the
Building or the Premises, it shall first submit to Landlord a written request
for Landlord's approval of the same, accompanied by a complete set of plans and
specifications relative thereto; Landlord shall, within fourteen (14) calendar
days after its receipt of Tenant's request, notify Tenant whether Landlord
approves or disapproves such request of Tenant (and in the event that Landlord
shall disapprove such request, Landlord shall in writing specify the reason or
all of the reasons for such disapproval). In the event that Landlord shall fail,
prior to the expiration of said fourteen (14) day period, to notify Tenant in
writing of its approval or disapproval of said request, Landlord shall be deemed
to have approved the same. All such approved Structural Alterations shall be
constructed at Tenant's sole cost and expense and shall be effected in
accordance with the plans and specifications approved (or deemed to have been
approved) by Landlord, in a good workmanlike manner and in accordance with all
valid requirements of municipal or other governmental authorities. All permanent
structural improvements shall belong to the Landlord and become a part of the
Premises upon termination or expiration of this Lease. Notwithstanding the
foregoing, Landlord does hereby agree that Tenant shall have the unrestricted
right to perform any alterations,

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additions, repairs or improvements to the Premises ("Tenant Alterations")
necessary or desirable to effect the following:

         (a) the installation of Tenant's telecommunications equipment and the
chases, conduits, cabling and connections related thereto;

         (b) the installation of a generator (and associated generator pad and
fuel tank) adjacent to the Building either (i) in the "cross-hatched" area shown
on Exhibit D; or (ii) in any area on the Premises no larger than six (6) square
feet located outside the "cross-hatched" area shown on Exhibit D which shall be
in compliance with the requirements of all municipal and other governmental
authorities; provided, however, that in the event that Tenant shall elect so to
install the same outside of the "cross-hatched" area depicted on Exhibit D,
Tenant shall, upon request by Landlord and at its sole cost and expense, cause
the same to be removed from the Premises at the termination or prior expiration
of the Term hereof and shall repair and restore any portion of the Premises
damaged as a result thereof;

         (c) the installation of Tenant's Dry Coolers and Liebert Glycol units
and any vents associated therewith;

         (d) the installation of HVAC equipment and any drains associated
therewith;

         (e) the removal of the HVAC system currently servicing the Building
(provided the same does not interfere with the HVAC services that Landlord is
obligated to supply to the First Floor Space under the First Floor Lease);

         (f) the installation of a GPS antenna (and related base site cabinets
associated therewith), in an area on the roof of the Building being no larger
than six (6) square feet;

         (g) the installation of an independent fire suppression system; and

         (h) the removal and capping of any portion of the heating system.

         In addition to the Tenant Alterations and as a material inducement for
Landlord's entering into this Lease with Tenant, Tenant does hereby agree, at
its sole cost and expense and utilizing plans and specifications reasonably
acceptable to Landlord, that Tenant will, on or before the Rent Commencement
Date, replace the roof of the Building with a replacement "20 year" roof (the
"Roof Replacement") meeting the minimum standards hereafter mutually agreed upon
in advance of construction by Landlord and Tenant, each acting reasonably and in
good faith, with such minimum standards to be integrated into the plans and
specifications for the Roof Replacement described herein.

         Upon completion of the Roof Replacement, Tenant shall promptly assign
to Landlord all warranties and guaranties relative to the installation of and
materials utilized in said Roof Replacement which shall have been obtained by
Tenant in connection with the Roof Replacement.

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         Prior to construction, but in no event later than the sixtieth (60th)
calendar day following the Commencement Date, Tenant shall deliver to Landlord a
complete set of plans and specifications relative to the Tenant Alterations and
the Roof Replacement. All of the Tenant Alterations, the Roof Replacement, and
any future Structural Alterations shall be installed and maintained in
accordance with all applicable governmental rules, regulations, codes, laws and
ordinances. Tenant shall also be responsible for all repairs, replacements
and/or upgrades required, to the structure and roof of the Building caused by
the installation and/or maintenance of the Tenant Alterations, the Roof
Replacement, any Structural Alterations and Tenant's specific use. Any and all
of Tenant's contractors must be properly licensed, insured and bonded.

         Except for those portions of the Tenant Alterations consisting of fire
suppression demising walls, the cabling for Tenant's telecommunications
equipment and the sprinkler system (which Tenant shall not be obligated to
remove from the Premises upon the expiration or earlier termination of this
Lease, and if not so removed, shall be deemed abandoned by Tenant and shall
automatically become the property of Landlord), all of the Tenant Alterations
shall remain the property of Tenant and will be removed from the Premises by
Tenant upon the expiration or earlier termination of this Lease provided Tenant
repairs any damage done to the Building and the Premises by such removal.
Notwithstanding the foregoing, all permanent structural improvements (including
the Roof Replacement) and any new HVAC units installed by Tenant (including,
without limitation, those referred to in [d] immediately hereinabove) shall
remain the property of Landlord upon the expiration or earlier termination of
this Lease.

         On or before the tenth (10th) calendar day after Tenant delivers to
Landlord a written request for reimbursement, together with reasonably
satisfactory substantiating documentation, Landlord shall reimburse Tenant for
any cost incurred by Tenant, up to a total of $5,000.00, in connection with any
structural analysis of the Premises. In the event Landlord shall fail to pay
such amount, Tenant shall have the right to offset or credit such amount against
any Rent, Additional Rent or other sum payable to Landlord by Tenant under this
Lease.

         To the maximum extent permitted by applicable Laws, Landlord hereby
waives any rights which Landlord may have, as to any of Tenant's furniture,
fixtures, equipment and personal property and Tenant Alterations, in the nature
of a landlord's lien, security interest or otherwise and further waives the
right to enforce any such lien or security interest. Landlord further
acknowledges that certain equipment to be installed by Tenant in the Premises
is leased and subject to the ownership rights of third-party equipment
landlords. Landlord hereby agrees that such third-party landlords may enter into
the Premises and remove such equipment, provided any damage to the Premises
caused thereby is restored. Notwithstanding the foregoing, in the event that
neither Tenant nor any such third-party landlord shall remove from the Premises,
on or before the thirtieth (30th) calendar day after the expiration or earlier
termination of the Lease, such furniture, fixtures, equipment or personal
property or those items of the Tenant Alterations which Tenant is required to
remove from the Premises in accordance with the provisions of this Section 9.,
all such items shall be deemed abandoned by Tenant and such third-party
landlords and, at the option of Landlord, shall become the property of Landlord,
or at Landlord's option, may be removed by Landlord at Tenant's expense, or sold
or otherwise disposed of, in which event the proceeds of such sale or other
disposition shall

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belong to Landlord, and Tenant shall be liable to pay Landlord's costs and
expenses in connection therewith, together with a sum equal to fifteen percent
(15%) of such costs and expenses to cover Landlord's overhead therefore. Upon
request, Landlord agrees to execute and deliver a Landlord's Consent and
Subordination Agreement for the benefit of Tenant's equipment landlord in
substantially the form set forth in Exhibit C hereto; and, in addition, Landlord
does hereby also agree that it will act reasonably and in good faith to reach a
mutually acceptable Landlord's Consent and Subordination Agreement with Tenant's
equipment landlord.

         10. Environmental. Tenant shall not cause or permit any hazardous or
toxic substances, materials or waste ("Hazardous Substances") to be used,
generated, stored or disposed of in, on or under, or transported to or from the
Premises in violation of any local, state, and federal laws, ordinances, rules,
regulations and orders, whether now in existence or hereafter adopted relating
to Hazardous Substances or otherwise pertaining to the environment (the
"Environmental Laws").

         Tenant shall indemnify, defend (by counsel reasonably acceptable to
Landlord), protect, and hold Landlord harmless, from and against any and all
claims, liabilities, penalties, fines, judgment, forfeitures, losses, costs
(including clean-up costs) or expenses (including attorney's fees, consultant's
fees and expert's fees), including, without limitation, those related to the
death of or injury to any person or damage to any property whatsoever, arising
from or caused in whole or in part, directly or indirectly, by (a) the presence
after the Commencement Date in, on, under, or about the Premises of any
Hazardous Substances caused by Tenants or its agents, servants, employees,
guests, invitees and/or independent contractors, (b) any discharge or release by
Tenant or its agents, servants, employees, guests, invitees and/or independent
contractors after the Commencement Date in or from the Premises of any Hazardous
Substances, (c) Tenant's use, storage, transportation, generation, disposal,
release or discharge after the Commencement Date of Hazardous Substances, to,
in, on, under, about or from the Premises, (d) Tenant's failure after the
Commencement Date to comply with any Environmental Law; or (e) the disturbance,
handling, removal or treatment by Tenant or any of Tenant's employees, agents,
servants, guests, invitees and/or independent contractors, of any Hazardous
Substance identified as being present on, in or under the Premises in either
that certain Phase I Environmental Assessment dated October, 1997, prepared by
Roy F. Weston, Inc. for The Austin Company or that certain Hazardous Materials
Survey Report dated October, 1997, prepared by Roy F. Weston, Inc. for The
Austin Company, copies of which have been delivered to Tenant (collectively, the
"Environmental Reports").

         Except only to the extent arising from the disturbance, handling,
removal or treatment of any Hazardous Substance identified as being present in,
on or under the Premises in the Environmental Reports by Tenant or any of
Tenant's employees, agents, servants, guests, invitees and/or independent
contractors, Landlord shall indemnify, defend (by counsel reasonably accepted to
Tenant), protect, and hold Tenant harmless, from and against any and all claims,
liabilities, penalties, fines, judgment, forfeitures, losses, costs (including
clean-up costs) or expenses (including attorney's fees, consultant's fees and
expert's fees), including, without limitation, those related to the death of or
injury to any person or damage to any property whatsoever, arising from or
caused in whole or in part, directly or indirectly, by (a) the presence prior to
the Commencement Date in, on, under, or about the Premises of any Hazardous
Substances, (b) any discharge or release prior to the

                                       11
<PAGE>   12
Commencement Date in or from the Premises of any Hazardous Substances, (c) the
use, storage, transportation, generation, disposal, release or discharge of
Hazardous Substances by Landlord or Landlord's prior Tenant(s) prior to the
Commencement Date, to, in, on, under, about or from the Premises, or (d)
Landlord's failure prior to the Commencement Date to comply with any
Environmental Law.

         Landlord represents and warrants to Tenant that, except as set forth in
the Environmental Reports, as of the Commencement Date and to the best of
Landlord's knowledge there are no Hazardous Substances in, on, under, about or
flowing from the Premises. Landlord has received no notice from any governmental
or private entity relating to Hazardous Substances on the Premises. Tenant shall
promptly deliver to Landlord copies of all notices made by Tenant to, or
received by Tenant from, any state, county, municipal or other agency having
authority to enforce any Environmental Law ("Enforcement Agency") or from the
United States Occupational Safety and Health Administration concerning
environmental matters or Hazardous Substances at the Premises. Landlord shall
promptly deliver to Tenant copies of all notices received by Landlord from any
Enforcement Agency or from the United States Occupational Safety and Health
Administration concerning environmental matters or Hazardous Substances at the
Premises.

         11. Casualty Damage.

         (a) Should the Premises be partially destroyed by fire or other
casualty, the Landlord will, with all due diligence and in not less than
one-hundred fifty (150) days at its own expense, (i) repair or restore the same
so that thereafter the Premises shall be substantially in the same condition as
originally delivered to Tenant; and (ii) repair and restore any of the Tenant
Alterations covered by Landlord's Property Insurance. In such event, Rent and
Additional Rent shall equitably abate in proportion to the nature and extent of
interference to Tenant's use and occupancy of the Premises from the date of such
damage until Landlord's repair or restoration is complete, and for such
reasonable additional time not to exceed ninety (90) days as is required for
Tenant to complete its work and prepare for the recommencement of its business
in the Premises.

         (b) Should the Premises be so extensively damaged by fire or other
casualty as to require rebuilding, then the Landlord shall promptly, at its own
expense, (i) restore or rebuild the same so that thereafter the Premises shall
be in substantially the same condition as originally delivered to Tenant; and
(ii) repair and restore any of the Tenant Alterations covered by Landlord's
Property Insurance. Rent and Additional Rent shall abate equitably in proportion
to the nature and extent of interference to Tenant's use and occupancy of the
Premises from the date of damage to the date such possession is tendered to the
Tenant, and for such reasonable additional time not to exceed ninety (90) days
as is required for Tenant to complete its work and prepare for the
recommencement of its business in the Premises.

         (c) Notwithstanding the foregoing or anything to the contrary herein
contained, (i) if more than thirty percent (30%) of the Building shall be
destroyed by fire or other casualty in the last five (5) years of the initial
Term (or any extended Term hereof) and Tenant does not exercise any renewal
options available to it or negotiate a new Lease to extend the remaining Term to
at least five (5) years, or (ii) if any mortgagee of the Premises requires
application of insurance proceeds to the

                                       12
<PAGE>   13
reduction of the mortgage debt, or if any material uninsured loss occurs (i.e. a
loss not covered by the insurance required to be maintained by Landlord under
the provisions of Section 16. hereinbelow), then Landlord, at its option, may
terminate this Lease by giving written notice to Tenant within sixty (60) days
after the occurrence of such damage or destruction. Any such termination shall
be effective on the date specified therefor in Landlord's notice to Tenant. If
Tenant does not elect to terminate this Lease as provided in (d) hereinbelow,
and if Landlord elects to or is required to repair or rebuild the Premises as
herein provided, Tenant shall repair or replace its Tenant Alterations, trade
fixtures, furnishings and equipment.

         (d) Notwithstanding the foregoing or anything to the contrary herein
contained, (i) if more than thirty percent (30%) of Building shall be destroyed
by fire or other casualty, and (ii) if such damage occurs in the last two (2)
years of the initial Term (or any extended Term hereof) then Tenant, at its
option, may terminate this Lease by giving written notice to Landlord within
sixty (60) days after the occurrence of such damage or destruction. Any such
termination shall be effective on the date specified therefor in Tenant's notice
to Landlord. If the Tenant does not elect to terminate this Lease as herein
provided, and if Landlord is required to repair or rebuild the Premises as
herein provided, Tenant shall repair or replace its Tenant Alterations, trade
fixtures, furnishings and equipment.

         (e) In the event Landlord is required to or elects to restore the
Premises, as the case may be pursuant to Paragraphs (a), (b) and (c) above,
Landlord shall deliver the restored Premises to Tenant no later than one-hundred
eighty (180) days from the date of casualty, and if Landlord fails to so deliver
the restored Premises, Tenant shall have a continuing right to terminate the
Lease, in addition to all other remedies available to it.

         12. Condemnation. If all or substantially all of the Premises is
condemned or is sold in lieu of condemnation, then this Lease shall terminate on
the date the condemning authority takes possession. If less than all of the
Premises is so condemned or sold and in Landlord's judgment, the Premises cannot
be restored to an economically viable condition, or if any mortgagee of the
Premises requires application of the condemnation proceeds to the reduction of
the mortgage debt, Landlord may terminate this Lease by written notice to Tenant
effective on the date the condemning authority takes possession. If the
condemnation will render any substantial part of the Building untenantable,
Tenant may terminate this Lease by written notice to Landlord effective on the
date the condemning authority takes possession of the affected part of the
Building. If this Lease is not so terminated by Landlord or Tenant, Landlord
shall, to the extent feasible, restore the Premises to substantially their
former condition. Landlord shall not, however, be required to restore any
alterations (including the Tenant Alterations), additions, or improvements or to
spend any amount in excess of the condemnation proceeds actually received by
Landlord. Landlord shall allow Tenant an equitable abatement of Rent and
Additional Rent during the time and to the extent the Building is untenantable
as the result of any condemnation, but such abatement shall not extend the term.
Except only to the extent that the unamortized cost of the Tenant Alterations is
included in the condemnation award or proceeds received by Landlord (in which
event the amount identified as separately payable for said unamortized Tenant
Alterations [or, if not separately identified, an amount reasonably allocable to
said unamortized Tenant Alterations] shall promptly after receipt be paid by
Landlord to Tenant),

                                       13
<PAGE>   14
all condemnation awards and proceeds shall belong exclusively to Landlord, and
Tenant shall not be entitled to, and expressly waives and assigns to Landlord,
all claims for any compensation of condemnation; provided, however, if Tenant is
permitted by applicable law to maintain a separate action that will not reduce
condemnation awards or proceeds to Landlord, Tenant shall be permitted to pursue
such separate action, but only for loss of business, moving expenses, and
Tenant's trade fixtures, equipment and the Tenant Alterations.

         13. Liens. Tenant shall not permit to be created nor to remain
undischarged any lien, encumbrance or charge arising out of any work or work
claim of any contractor, mechanic, laborer of Tenant or material supplied by a
materialman to Tenant which might be, or become, a lien or encumbrance or charge
upon the Premises. If any lien or notice of lien on account of an alleged debtor
of Tenant or any notice of contract by a party engaged by Tenant or Tenant's
contractor to work in the Premises shall be filed against the Premises, Tenant
shall, within thirty (30) days after notice of the filing thereof, cause the
same to be discharged of record by payment, bonded or insured over by Landlord's
title company.

         14. Indemnity. Tenant agrees to indemnify Landlord and save Landlord
harmless from any and all liability, claims and loss for personal injury or
property damage, or both, sustained or claimed to have been sustained by any
person or persons, or property in or upon the Premises accruing or arising from
and after the Commencement Date. Landlord agrees to indemnify Tenant and save
Tenant harmless from any and all liability, claims and loss for personal injury
or property damage, or both, sustained or claimed to have been sustained by any
person or persons, or property in or upon the Premises accruing or arising on or
before the Commencement Date.

         15. Events of Default by Tenant.

         A. Tenant Default. Each of the following constitutes an event of
default (an "Event of Default") by Tenant:

         (a) Tenant fails or refuses to pay any installment of Rent, Additional
Rent, or any other sum payable under this Lease when due, and the failure or
refusal continues for at least five (5) days after the due date; provided,
however, that, with respect to the first (1st) two (2) such failures to timely
pay during any Lease Year only, no Event of Default on the part of Tenant shall
be deemed to have occurred if Tenant cures such failure on or before the fifth
(5th) business day after the delivery of written notice of such failure from
Landlord to Tenant.

         (b) Tenant fails or refuses to comply with any provision of this Lease
not requiring the payment of money, and the failure or refusal continues for at
least thirty (30) days after written notice from Landlord; provided, however, if
any failure by Tenant to comply with this Lease cannot be corrected within such
30-day period solely as a result of nonfinancial circumstances outside of
Tenant's control, and if Tenant has commenced substantial corrective actions
within such 30-day period and is diligently pursuing such corrective actions,
such 30-day period shall be extended for such additional time as is reasonably
necessary to allow completion of actions to correct Tenant's noncompliance.

                                       14
<PAGE>   15
         (c) Tenant's leasehold estate is taken on execution or other process of
law in any action against Tenant.

         (d) Tenant fails or refuses to take occupancy of the Premises on or
before the ninetieth (90th) calendar day following the Rent Commencement Date.

         (e) Tenant files a petition under any chapter of the United States
Bankruptcy Code, as amended, or under any similar law or statute of the United
States or any state, or petition is filed against Tenant or any such guarantor
under any such statute and not dismissed with prejudice within twenty (20) days
of filing, or a receiver or trustee is appointed for Tenant's leasehold estate
or for any substantial part of the assets of Tenant and such appointment is not
dismissed with prejudice within sixty (60) days, or Tenant makes an assignment
for the benefit of creditors.

         B. Landlord's Remedies. If an Event of Default by Tenant occurs,
Landlord shall be entitled at any time thereafter to exercise any right or
remedy available to Landlord under the laws of the State of Georgia as a result
thereof, including, without limitation, at Landlord's option, the actions
described hereinbelow:

         (a) Enter the Premises if need be, and take whatever curative actions
are necessary to rectify Tenant's noncompliance with this Lease; and in that
event Tenant shall reimburse Landlord on written demand for any expenditures by
Landlord to effect compliance with Tenant's obligations under this Lease.

         (b) Terminate this Lease, in which event Tenant shall immediately
surrender possession of the Premises to Landlord, or without terminating this
Lease, terminate Tenant's right to possession of the Premises, and in either
case, Landlord may re-enter and take possession of the Premises, evict Tenant
and all parties then in occupancy or possession, and if permitted under
applicable law, change the locks on the doors of the Premises without making
keys to the changed locks available to Tenant.

         (c) If Landlord has terminated this Lease, recover all Rent, Additional
Rent, and other sums owing and unpaid under this Lease as of the date of
termination plus damages measured by the difference (discounted to a present
value) in the rental value of the Premises if this Lease had been fully
performed for the balance of the term and the rental value of the Premises
following the Event of Default by Tenant (taking into account probable
remodeling, lease commission, allowance, inducement, and other costs of
reletting).

         (d) If Landlord has not terminated this Lease (whether or not Landlord
has terminated Tenant's right to possession of the Premises or actually retaken
possession), recover (in one or more suits from time to time or at any time
before or after the end of the term) all Rent, Additional Rent, and other sums
then or thereafter owing and unpaid under this Lease, together with all costs,
if any, incurred in reletting the Premises (including remodeling, lease
commission, allowance, inducement, and other costs), less all rent, if any,
actually received from any reletting of the Premises during the remainder of the
term. Landlord shall have the night following an Event of Default by Tenant to
relet the Premises on Tenant's account without terminating the Lease, and agrees
to use reasonable efforts

                                       15
<PAGE>   16
to do so; provided, however, that any such reletting shall be on such terms as
Landlord, in its sole and absolute discretion, considers reasonable under the
circumstances.

         (e) Recover all costs of retaking possession of the Premises and any
other damages incidental to the Event of Default by Tenant.

         (f) Terminate all of Tenant's rights to any allowances or under any
renewal, extension, expansion, refusal, or other options granted to Tenant by
this Lease.

         (g) Exercise any and all other remedies available to Landlord at law or
in equity, including injunctive relief of all varieties.

         If Landlord elects to retake possession of the Premises without
terminating this Lease, it may nonetheless at any subsequent time elect to
terminate this Lease and exercise the remedies provided above on termination of
the Lease. Nothing done by Landlord or its agents shall be considered an
acceptance of any attempted surrender of the Premises unless Landlord
specifically so agrees in writing. No re-entry of taking of possession of the
Premises by Landlord, nor any reletting of the Premises, shall be considered an
election by Landlord to terminate this Lease unless Landlord gives Tenant
written notice of termination.

         16. Insurance.

         (a) Landlord agrees to carry, or cause to be carried, during the Term
hereof, as primary general liability insurance, Commercial General Liability
("Landlord's Liability Insurance") on the Premises, naming Tenant as an
additional insured, providing coverage of not less than Three Million Dollars
($3,000,000.00) in the aggregate for combined bodily injury and property damage
liability, with separate limits for each of not less than One Million Dollars
($1,000,000.00) per occurrence. Landlord, upon request, shall furnish Tenant a
certificate of such Landlord's Liability Insurance.

         Landlord also agrees to carry, during the Term hereof, all risk
property insurance ("Landlord's Property Insurance") covering fire and extended
coverage, vandalism and malicious mischief, sprinkler leakage and all other
perils of direct physical loss or damage insuring the improvements and
betterments located on the Premises and all appurtenances thereto (excluding
Tenant's property and the Tenant's Alterations) for the full replacement value
thereof (including rent loss insurance for a period reasonably determined by
Landlord as necessary to protect its interests). Landlord, upon request, shall
furnish Tenant a certificate of such Landlord's Property Insurance.

         Landlord agrees to use good faith efforts to obtain Landlord's
Liability Insurance and Landlord's Property Insurance at commercially reasonable
rates; and will, upon request by Tenant, obtain additional bids for the same.
During the Term of this Lease, Tenant agrees to reimburse Landlord for
Landlord's Insurance Costs in the manner described in Section 8. hereinabove.

         (b) Tenant agrees to carry, or cause to be carried, Commercial General
Liability on the Premises during the Term hereof covering both Tenant and
Landlord as their interests may appear, giving Landlord and Tenant a minimum of
thirty (30) days written notice by the insurance company

                                       16
<PAGE>   17
prior to cancellation or termination of such insurance. Such insurance shall be
for limits of not less than Three Million Dollars ($3,000,000.00) in the
aggregate for combined bodily injury and property damage, with separate limits
of not less than One Million Dollars ($1,000,000.00) per occurrence.

         Tenant further agrees to carry all risk property insurance ("Tenant's
Property Insurance") covering, fire and extended coverage, vandalism and
malicious mischief, sprinkler leakage and all other perils of direct physical
loss or damage for at least eighty percent (80%) of the replacement value, all
of Tenant's property (including, without limitation, the Tenant Alterations)
located on or within the Premises. Tenant shall provide Landlord certificates
evidencing that Tenant's Property Insurance is in full force and effect.
Landlord agrees that it shall not have any right, title or interest in and to
Tenant's Property Insurance, or any proceeds therefrom.

         (c) All of the insurance coverage to be maintained by Tenant or
Landlord as described herein, shall be procured and maintained with insurance
companies having at least a B++ rating.

         17. Waiver of Subrogation. Each of the parties hereto hereby releases
the other and the other's partners, members, agents and employees, to the extent
of each party's insurance coverage, from any and all liability for any loss or
damage which may be inflicted upon the property of such party even if such loss
or damage shall be brought about by the fault or negligence of the other party,
its partners, members, agents or employees; provided, however, that this release
shall be effective only with respect to loss or damage occurring during such
time as the appropriate policy of insurance shall contain a clause to the effect
that this release shall not affect said policy or the right of the insured to
recover thereunder. If any policy does not permit such a waiver, and if the
party to benefit therefrom requests that such a waiver be obtained, the other
party agrees to obtain an endorsement to its insurance policies permitting such
waiver of subrogation if it is commercially available and if such policies do
not provide therefor.

         18. Repairs and Maintenance. Landlord, at its sole cost and expense,
shall maintain and keep in good order and repair and make any necessary
replacements to the roof, foundation, structural components, and exterior walls
of the Building; provided, however, that Landlord shall not be required to make
any repairs or replacements required as a result of the act or neglect of
Tenant, its employees, contractors, licensees, agents and/or invitees
(including, without limitation, the Tenant Alterations). Except for Landlord's
obligations set forth above and any repairs required as a result of a fire or
other casualty to which the provisions of Section 11. are applicable, Tenant
agrees, at its sole cost and expense, to keep in good order and operating
condition and repair all portions of the Building and the Premises, including,
but not limited to, all day-to-day maintenance and repair (and, if necessary,
replacement) of the Building, HVAC system, plumbing, electrical system, grounds
and parking lot, and shall take good care of the Premises and permit no waste
thereto.

         If Landlord shall not commence such repairs within the fifteen (15)
days following written notice from Tenant that such repairs are necessary then
Tenant may, at its option, cause such Landlord repairs to be made and shall
furnish Landlord with a statement of the reasonable and actual cost of such
repairs upon substantial completion thereof. Landlord shall reimburse Tenant for
the

                                       17
<PAGE>   18
reasonable and actual cost of such repairs within thirty (30) days of the date
of the statement from Tenant setting forth the amount due, provided, however,
should Landlord fail to reimburse Tenant with said thirty (30) day period, then
Tenant may, at its option, offset such amount against subsequent Rent and
additional rent due under this Lease.

         19. Brokers. With the exception of Corporate Property Advisors, Inc.,
who represented the Landlord, and Fisher & Company, who represented the Tenant,
Landlord and Tenant warrant and represent, each to the other, that it has had no
dealings with any broker or agent in connection with this Lease, and Landlord
and Tenant hereby indemnify each other against, and agree to hold each other
harmless from, any liability or claim (and all expenses, including, attorney's
fees incurred in defending any such claim or in enforcing this indemnity) for a
real estate brokerage commission or similar fee or compensation arising out of
or in any way connected with any claimed dealings with the indemnitor and
relating to this Lease or the negotiating thereof. Corporate Property Advisors,
Inc. and Fisher & Company will be paid a commission by Landlord pursuant to a
separate commission agreement.

         20. Emergency. If Landlord is unable or unwilling to take action which
it is obligated to take hereunder where an emergency has occurred with respect
to the Premises, then Tenant may take such action as is reasonably necessary to
protect the Premises and persons or property in the Premises and Landlord shall,
within thirty (30) days after written notice thereof from Tenant reimburse
Tenant for its reasonable and actual out-of-pocket expenses incurred in curing
such emergency; provided, however, should Landlord fail to reimburse Tenant
within said thirty (30) day period, then Tenant may, at its option, offset such
amount against subsequent rent due under this Lease.

         21. Title. Landlord hereby represents that Landlord is the owner in fee
simple of the Premises, including the Building and all improvements thereon free
from any liens or encumbrances (other than the encumbrances and other matters
identified as exceptions in the Owner's Policy of Title Insurance issued to
Landlord by Chicago Title Insurance Company dated April 7, 1998 [Policy Number
11-0107-106-00000083]), a copy of which has been delivered by Landlord to
Tenant, which Landlord represents will not prohibit or interfere with Tenant's
intended use of the Premises as a telecommunications switch site). Landlord
further represents that Landlord has the right and authority to enter into this
Lease and that those signatories executing this Lease on behalf of Landlord have
full power and authority to execute this Lease.

         Landlord agrees that Landlord will not make any modifications to the
Premises which would interfere with Tenant's use of the Premises as a
telecommunications switch site.

         22. Compliance with Laws. Landlord represents and warrants to Tenant
that, to the best of its actual knowledge without investigation or inquiry, as
of the Commencement Date, the Premises are in compliance with applicable
federal, state and local laws, ordinances, rules and regulations ("Laws"),
including, without limitation, applicable zoning laws, ordinances, rules and
regulations and with applicable instruments affecting title to the Premises.
Notwithstanding the foregoing, Landlord represents that the Premises are not and
to date have not been required to be in compliance with the Americans with
Disabilities Act.

                                       18
<PAGE>   19
         If at any time or from time to time any Alterations, including, without
limitation, structural Alterations, are required in order for the Premises to
comply with any Laws from time to time applicable to the Premises, Tenant shall
immediately make such Alterations at its sole cost and expense.

         23. Tenant to Subordinate. Tenant shall, upon request of the holder of
a mortgage or deed of trust in the nature of a mortgage, which holder is a
commercial or institutional lender ("Mortgagee") subordinate any interest which
it has by virtue of this Lease, and any extensions and renewals thereof to any
mortgages or deeds of trust placed upon the Premises by Landlord, if and only if
such Mortgagee shall execute, deliver and record in the appropriate registry of
deeds a recognition and non-disturbance agreement in form and content generally
used in commercial loan transactions and approved by Tenant, such approval not
to be unreasonably withheld. Such Agreements shall provide by their terms that
notwithstanding any foreclosure of such mortgage or deeds of trust Tenant may
continue to occupy the Premises during the Term or any extensions or renewals
thereof under the same terms, conditions and provisions of this Lease unless
Tenant shall be in default beyond any applicable grace periods provided for
herein. Landlord shall at or prior to the sixtieth (60th) calendar day following
the Commencement Date, secure from Landlord's present mortgagee of the Premises
a non-disturbance agreement in a form reasonably acceptable to Tenant.

         24. Quiet Enjoyment. Landlord agrees that, that so long as no Event of
Default on the part of Tenant shall be in existence, Tenant shall have
continuous, peaceful, uninterrupted and exclusive possession and quiet enjoyment
of the Premises during the Term of this Lease, as such Term may be extended.

         25. Memorandum of Lease. Landlord agrees to enter into and record a
memorandum or notice of this Lease reasonably satisfactory to Tenant and
Landlord. Tenant shall be responsible for the preparation thereof and the cost
of recording the same.

         26. Notices. All notices, demands and requests which may be or are
required to be given by either party to the other shall be in writing and shall
be either (i) sent by registered or certified mail, return receipt requested,
postage prepaid or (ii) delivered, by hand, or (iii) sent by overnight courier
such as Federal Express. All notices to Landlord should be addressed to Landlord
at 5755 Dupree Drive, Suite 110, Atlanta, Georgia 30327-4325, Attention: Mr.
Steven M. Schwartz, with a copy to Marshall E. Siegel, Esq., Siegel & Golder,
P.C., One Premier Plaza, 5605 Glenridge Drive, Suite 690, Atlanta, Georgia
30342, or at such other place as Landlord may from time to time designate in
written notice to Tenant. All notices to Tenant shall be addressed to Tenant c/o
2180 Fox Mill Road, Herndon, Virginia 20171, Attention: Legal Department, with a
copy to Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., Attention: Daniel
O. Gaquin, Esq., One Financial Center, Boston, Massachusetts 02111, or to any
such other place as Tenant may from time to time designate in written notice to
Landlord. All notices, demands and requests which shall be served upon Landlord
and Tenant in the manner aforesaid shall be deemed sufficiently served or given
for all purposes hereunder.

         27. Estoppel Certificate. Each of Landlord and Tenant agrees at any
time and from time to time upon not less than ten (10) days prior written
request by the other to execute, acknowledge

                                       19
<PAGE>   20
and deliver to the other a statement in writing certifying that (a) this Lease
is unmodified and in full force and effect (or if there have been modifications
that the same is in full force and effect as modified and stating the
modifications), (b) the dates to which the Rent and other charges have been paid
in advance, if any, and (c) all of the defaults of Landlord or Tenant hereunder,
if any, (and if there are no defaults a statement to that effect) and any other
information reasonably requested, it being intended that any such statement
delivered pursuant to this Section 27 may be relied upon by any prospective
purchaser of the Premises or any mortgagee or assignee of any mortgage upon the
fee or leasehold of the Premises or by any prospective assignee of this Lease or
subtenant of the whole or any portion of the Premises and/or by other party
interested in the Premises or any part thereof.

         28. Holding Over. If Tenant remains in possession of any part of the
Premises after the expiration of the Term of this Lease, whether with or without
Landlord's consent, Tenant shall be only a tenant at will, the monthly
installments of Rent payable during such holdover period shall be one hundred
fifty percent (150%) of the monthly installments of Rent payable immediately
preceding such expiration, and all Additional Rent and other sums payable under
this Lease shall continue to be due and payable. The acceptance of any Rent,
Additional Rent or other payments from Tenant with respect to any holdover
period shall not serve to extend the term or waive any rights of Landlord, but
Landlord may at any time refuse to accept Rent or other payments from Tenant,
and may re-enter the Premises, evict Tenant and all parties then in occupancy or
possession, take possession of the Premises, and if permitted under applicable
law, change the locks on the doors of the Premises without making keys to the
changed locks available to Tenant. Tenant shall indemnify and hold Landlord
harmless against any loss, liability, damage, cost, or expense (including
attorneys' fees and costs of litigation), or any claim therefor, related to
Tenant's holding over, including liabilities to any person to whom Landlord may
have leased any part of the Premises.

         29. Binding Effect. All covenants, agreements, stipulations,
provisions, conditions and obligations herein expressed and set forth shall
extend to, bind and inure to the benefit of, as the case may require, the
successors and assigns of Landlord and Tenant respectively, as fully as if such
words were written wherever reference to Landlord or Tenant occurs in this Lease

         30. Complete Agreement. Any stipulations, representations, promises or
agreements, oral or written, made prior to or contemporaneously with this
agreement shall have no legal or equitable consequences and the only agreement
made and binding upon the parties with respect to the leasing of the Premises is
contained herein, and it is the complete and total integration of the intent and
understanding of Landlord and Tenant with respect to the leasing of the
Premises.

         31. Landlord's Right of Entry. Landlord and persons authorized by
Landlord may enter the Premises, after first having attempted to notify Tenant
by telephone, in the event of emergency involving possible injury to property or
persons in or around the Premises or the Building; and in the event of any such
emergency, Landlord and persons authorized by Landlord agree to be escorted in
and around the Premises by an employee of Tenant, if at the time such an
employee is available to do so. Subject to the restrictions described herein,
Landlord and persons authorized by Landlord shall have the right to enter the
Premises at all reasonable times and upon not less than forty-eight

                                       20
<PAGE>   21
(48) hours advance written notice, for the purposes of making repairs or
connections, making alterations, additions, or improvements to the Building,
installing utilities, providing services to the Premises or for making
inspections, or showing the Premises to prospective purchasers or lenders of the
Premises. During the last six (6) months of the initial or any extended Term,
Landlord and persons authorized by Landlord shall have the right at reasonable
times and upon reasonable notice to show the Premises to prospective tenants and
Landlord shall have the right to place a "For Lease" sign on the Property.
Landlord acknowledges that the Building, including, without limitation, Tenant's
switch site area, shall constitute a secure area. Tenant will be installing
elaborate security systems, which may include a palm-reader and a card access
system, to safeguard entry and access to the Building. Such being the case,
Landlord agrees, notwithstanding the provisions of this Section to the contrary,
that in all instances (except for an emergency situation, the protocol for which
is specifically addressed in a different manner immediately hereinabove),
Landlord will only enter and move in and about the Premises with an escort
designated by Tenant. In any instance where Landlord or any agents thereof
enters upon the Premises, whether to make repairs, alterations or improvements
or otherwise, Landlord and any such agents shall use all reasonable efforts to
prevent any disruption to or interference with the business activities being
conducted by Tenant in the Premises.

         32. Limitation of Liability.

         (a) Tenant agrees to look solely to the Landlord's then current
interest in the Premises for the payment of any monetary damages arising out of
this Lease; it being specifically understood and agreed that neither Landlord
nor any trustee, shareholder, director, officer, partner, member or joint
venturer of any of the foregoing shall ever be personally liable for any such
monetary obligation or judgment. In no event shall Landlord be liable for any
indirect, incidental, special, consequential, exemplary or punitive damages
(including, but not limited to damages for lost profits or lost revenues),
whether or not caused by the acts, or omissions or negligence of its employees
or agents, and regardless of whether Landlord has been informed of the
possibility or likelihood of such damages.

         (b) In addition, it is hereby specifically understood and agreed that
no trustee, director or officer of Tenant shall ever be personally liable for
any such monetary obligation or judgment; provided, however, that the foregoing
shall not be deemed to release, modify or affect in any way the obligations of
Net2000 Communications Group, Inc., a Delaware corporation (the parent of
Tenant) under the terms of that certain Guaranty executed by said Net2000
Communications Group, Inc. in favor of Landlord in connection with the execution
of this Lease by Landlord and Tenant and as a material inducement therefor.

         33. Severability. If any term, covenant or condition of this Lease or
the application thereof to any person or circumstance shall, to any extent, be
invalid or unenforceable, the remainder of this Lease, or the application of
such term, covenant or condition to persons or circumstances other than those as
to which it is held invalid or unenforceable, shall not be affected thereby and
each term, covenant or condition of this Lease shall be valid and be enforced to
the fullest extent permitted by law.

                                       21
<PAGE>   22
         34. Applicable Law. This Lease shall be governed by and construed in
accordance with the laws of the State of Georgia, excluding its conflict of law
principles. The parties specifically waive jury trial.

         35. Time of the Essence. Time is of the essence with respect to the
performance of each of the covenants and agreements of this Lease.

         36. Transfer by Landlord. Landlord shall have the unrestricted right to
sell, assign, mortgage, encumber or otherwise dispose of all or any part of the
Premises or any interest therein. Tenant's obligations under this Lease shall
not be affected by any sale, assignment, mortgage, encumbrance or other
disposition of the Premises by Landlord, and Tenant shall attorn to anyone who
thereby becomes the successor to Landlord's interest in this Lease.

         37. Attorney's Fees. In the event that at any time during the Term of
this Lease either Landlord or Tenant shall institute any action or proceeding
against the other relating to the provisions of this Lease, or any default
hereunder, the unsuccessful party in such action or proceeding agrees to
reimburse the successful party for the reasonable expenses of attorney's fees
and paralegal fees and disbursements incurred therein by the successful party.
Such reimbursement shall include all legal expenses incurred prior to trial, at
trial and at all levels of appeal and post judgment proceedings, including
reasonable efforts to collect a judgment.

         38. Waiver. The failure of a party to insist upon the strict
performance of any provision of this Lease or to exercise any remedy for an
event of default shall not be construed as a waiver. The waiver of any
noncompliance with this Lease shall not prevent subsequent similar noncompliance
from being or becoming an event of default. No waiver shall be effective unless
expressed in writing signed by the waiving party. No waiver shall affect any
condition other than the one specified in the waiver and then only for the time
and in the manner stated. Landlord's receipt of any rent or other sums with
knowledge of noncompliance with this Lease by Tenant shall not be considered a
waiver of the noncompliance. No payment by Tenant of a lesser amount than the
full amount then due shall be considered to be other than on account of the
earliest amount due. No endorsement or statement on any check or any letter
accompanying any check or payment shall be considered an accord and
satisfaction, and Landlord may accept any check or payment without prejudice to
Landlord's right to recover the balance owing and to pursue any other available
remedies.

         39. Miscellaneous.

         (a) The relationship created by this Lease is that of Landlord and
Tenant. Landlord and Tenant are not partners or joint ventures, and neither has
any agency powers on behalf of the other. Tenant is not a beneficiary of any
other contract or agreement relating to the Property to which Landlord may be a
party, and Tenant shall have no right to enforce any such other contract or
agreement on behalf of itself, Landlord or any other party.

                                       22
<PAGE>   23
         (b) No consent or approval by Landlord shall be effective unless given
in writing signed by Landlord or its duly authorized representative. Any consent
or approval by Landlord shall extend only to the matter specifically stated in
writing.

         (c) Whenever this Lease requires Landlord's consent to or approval of
any item, Landlord may condition such consent or approval on payment or
reimbursement of all costs and expenses incurred by Landlord (including legal,
architectural, engineering, and other consulting services) as well as reasonable
administrative processing fee to compensate Landlord for its additional
administrative and overhead costs.

         (d) The captions appearing in this Lease are included solely for
convenience and shall never be given any effect in construing the Lease.

         (e) This Lease is being executed in multiple counterparts, each of
which shall be considered an original for all purposes.

         (f) All references to "business days" in this Lease shall refer to days
that national banks are open for business in the city where the Property is
located. Time is of the essence of this Lease.

         (g) All references to "mortgage(s)" in this Lease shall include deeds
of trust, deeds to secure debt, other security instruments, and any ground or
other lease under which Landlord may hold title to the Property as lessee. All
references to "mortgagee(s)" in the Lease shall include trustee, beneficiaries,
secured parties, ground or other lessors, and other parties secured by any
mortgage.

         (h) Any liability or obligation of Landlord or Tenant arising during or
accruing with respect to the term of this Lease shall survive the expiration or
earlier termination of this Lease, including without limitation, obligations and
liabilities relating to (i) the final adjustment of estimated installments of
Additional Rent to actual Additional Rent owed, (ii) the condition of the
Premises or the removal of Tenant's property, and (iii) indemnity and hold
harmless provisions of this Lease.

         (i) Tenant shall not record this Lease. Landlord and Tenant do hereby
agree to join in the execution of a memorandum or so called "short-form" of this
lease for the purposes of recordation. Any recording costs associated with the
recording of said memorandum or short form of this Lease shall be borne by the
party requesting the same.

                                       23
<PAGE>   24
         IN TESTIMONY WHEREOF, the Landlord and Tenant have caused this
agreement to be executed as a sealed instrument, as of the day and year first
above written.

                                   LANDLORD:

                                   PERIMETER CENTER INVESTORS, L.L.C., a Georgia
                                   limited liability company

                                   By: /s/ Steven M. Schwartz
                                       _________________________________________
                                         Steven M. Schwartz, Manager

                                   DOUBLE FEATURE, L.L,C., a Georgia limited
                                   liability company

                                   By: /s/ Steven M. Schwartz
                                       _________________________________________
                                         Steven M. Schwartz, Manager

                                   TENANT:

                                   NET2000 COMMUNICATIONS REAL ESTATE, INC.

                                   By: /s/ MA Mendez
                                       _________________________________________

                                        Title: COO
                                               _________________________________

                                       24
<PAGE>   25
                                   SCHEDULE I

                                 RENT SCHEDULE

<TABLE>
<CAPTION>
                    ANNUAL RENT RATE
   LEASE YEAR           (PER RSF)         ANNUAL RENT       MONTHLY RENT
   ----------           ---------         -----------       ------------
<S>                 <C>                   <C>               <C>
        1                $12.10           $282,341.40        $23,528.45
        2                $12.37           $288,641.58        $24,053.46
        3                $12.65           $295,175.10        $24,597.92
        4                $12.94           $301,941.96        $25,161.83
        5                $13.23           $308,708.82        $25,725.74
        6                $13.52           $315,475.68        $26,289.64
        7                $13.83           $322,709.22        $26,892.44
        8                $14.14           $329,942.76        $27,495.23
        9                $14.46           $337,409.64        $28,117.47
       10                $14.78           $344,876.52        $28,739.71

(if applicable)

       11                $15.12           $352,810.08        $29,400.84
       12                $15.46           $360,743.64        $30,061.97
       13                $15.80           $368,677.20        $30,723.10
       14                $16.16           $377,077.44        $31,423.12
       15                $16.52           $385,477.68        $32,123.14
       16                $16.89           $394,111.26        $32,842.60
       17                $17.27           $402,978.18        $33,581.52
       18                $17.66           $412,078.44        $34,339.87
       19                $18.06           $421,412.04        $35,117.67
       20                $18.47           $430,978.98        $35,914.92
</TABLE>
<PAGE>   26
                                   EXHIBIT A

                               LEGAL DESCRIPTION

All that tract or parcel of land lying and being in Land Lot 347 of the 18th
District of DeKalb County, Georgia, and being more particularly described as
follows:

TO FIND THE TRUE POINT OF BEGINNING, commence at the point formed by the
intersection of the easterly line of the right-of-way of Ashford-Dunwoody Road
as shown on that certain road dedication plat dated February 11, 1971, and
recorded March 24, 1971, in Plat Book 56, Page 144, Records of DeKalb County,
Georgia (such right-of-way being at such time a 40 foot right-of-way), and
the southerly right-of-way line of Perimeter Center East; running thence
easterly, southeasterly, southerly, easterly, northeasterly, and northerly
along the southerly, southwesterly, westerly, southerly, southeasterly, and
easterly lines of said right-of-way of Perimeter Center East, and following the
curvature thereof, a distance of 3,870.50 feet to an iron pin on said easterly
line of said right-of-way, said iron pin being at a point which is the POINT OF
BEGINNING.  FROM THE TRUE POINT OF BEGINNING AS THUS ESTABLISHED, running
thence northerly along said easterly line of said right-of-way, and following
the curvature thereof, a distance of 214.15 feet to an iron pin on said
easterly line of said right-of-way, said distance being measured along an arc
having a chord bearing north 08 degrees 30 minutes 58 seconds west a distance
of 213.21 feet; running thence north 17 degrees 49 minutes west a distance of
33.01 feet to an iron pin on said easterly right-of-way line; running thence
northwesterly along the northeasterly line of said right-of-way, and following
the curvature thereof, a distance of 31.50 feet to an iron pin on said
northeasterly line of said right-of-way, said distance being measured along an
arc having a chord bearing north 19 degrees 49 minutes 31 seconds west a
distance of 31.49 feet; running thence north 65 degrees 49 minutes 29 seconds
east a distance of 224.19 feet to an iron pin; running thence south 25 degrees
50 minutes 42 seconds east a distance of 298.02 feet to an iron pin; running
thence south 08 degrees 05 minutes 32 seconds west a distance of 115.57 feet to
an iron pin; running thence north 85 degrees 55 minutes 55 seconds west a
distance of 266.50 feet to an iron pin at a point on said easterly line of said
right-of-way of Perimeter Center East, being the Point of Beginning.

Said tract or parcel being 2.00000 acres and being shown on that certain survey
prepared for SouthTrust Bank, N.A., Double Feature, L.L.C., Perimeter Center
Investors, L.L.C. and Chicago Title Insurance Company dated February 11, 1998,
revised March 16, 1998, prepared by Larry R. McMullen, Georgia RLS #2317.
<PAGE>   27
                                   EXHIBIT B
                                PLAN OF PREMISES
                                  PAGE 1 OF 2

                                  [FLOOR PLAN]
<PAGE>   28
                                   EXHIBIT B
                                  PAGE 2 OF 2

                                  [FLOOR PLAN]
<PAGE>   29
                                   SCHEDULE A

                         LEGAL DESCRIPTION OF PREMISES
<PAGE>   30
                                   EXHIBIT D
                 48 PERIMETER CENTER EAST / GENERATOR LOCATION

                                   [DIAGRAM]
<PAGE>   31
                                    GUARANTY

     FOR AND IN CONSIDERATION of Ten Dollars ($10.00) and other good and
valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, and to induce PERIMETER CENTER INVESTORS, L.L.C., a Georgia
limited liability company, and DOUBLE FEATURE, L.L.C., a Georgia limited
liability company (collectively "Landlord"), to enter into the attached Lease
(the "Lease") with NET2000 COMMUNICATIONS REAL ESTATE, INC., a Delaware
corporation (hereinafter referred to as "Guarantor"), being the parent
corporation of Tenant, hereby absolutely and unconditionally guarantees to
Landlord, its successors and assigns, the payment of all Rent, Additional Rent
and any other sums due or to be due and payable in accordance with the terms of
the Lease and the performance by Tenant of all of its covenants and agreements
therein contained.  Guarantor hereby expressly waives notice of all Events of
Default, and hereby waives all suretyship defenses. Guarantor agrees that the
waiver of any rights by Landlord against Tenant arising out of an Event of
Default by Tenant shall not in any way modify or release the obligations of
Guarantor.

     This Guaranty and the obligations of Guarantor hereunder shall not be
released, modified or affected in any way by any future assignment of the
Lease or any amendment or modification thereof.

     This Guaranty shall inure to the benefit of Landlord, and its legal
representatives, successors and assigns; and shall be binding on the Guarantor
and its successors and assigns.

     IN WITNESS WHEREOF, Guarantor has caused this Guaranty to be executed by
its duly authorized officer, this 11th day of April, 2000.

                                                  GUARANTOR:

                                                  NET2000 COMMUNICATIONS GROUP,
                                                  INC., a Delaware corporation

                                                  By:  [SIG]
                                                   -----------------------------
                                                  Title: COO
                                                   -----------------------------

                                                  Attest: [SIG]
                                                  ------------------------------
                                                  Title: Director of Reg. & Law
                                                  ------------------------------<PAGE>   1
                                                                    Exhibit 10.2

                           LAKESIDE TECHNOLOGY CENTER
                              350 EAST CERMAK ROAD
                             CHICAGO, ILLINOIS 60616

                                 LEASE AGREEMENT

                                     BETWEEN

         CARLYLE-CORE CHICAGO LLC, A DELAWARE LIMITED LIABILITY COMPANY
                                  ("Landlord")

                                       AND

              NET2000 COMMUNICATIONS, INC., A DELAWARE CORPORATION
                                   ("Tenant")
<PAGE>   2
TABLE OF CONTENTS

<TABLE>
<S>                                                                          <C>
1.  BASIC LEASE INFORMATION .............................................      1
2.  LEASE GRANT .........................................................      4
3.  TERM; POSSESSION ....................................................      4
4.  RENT ................................................................      5
5.  COMPLIANCE WITH LAWS; USE ...........................................      9
6.  EQUIPMENT SPACE .....................................................     11
7.  SERVICES ............................................................     12
8.  ALTERATIONS .........................................................     15
9.  MAINTENANCE .........................................................     17
10. ENTRY BY LANDLORD ...................................................     17
11. ASSIGNMENT AND SUBLETTING ...........................................     17
12. LIENS ...............................................................     19
13. INDEMNITY AND WAIVER OF CLAIMS ......................................     19
14. INSURANCE ...........................................................     20
15. SUBROGATION .........................................................     21
16. CASUALTY DAMAGE .....................................................     21
17. CONDEMNATION ........................................................     22
18. SECURITY DEPOSIT ....................................................     22
19. EVENTS OF DEFAULT ...................................................     23
20. REMEDIES ............................................................     24
21. LIMITATION OF LIABILITY; LANDLORD'S TRANSFER ........................     25
22. NO WAIVER ...........................................................     25
23. QUIET ENJOYMENT .....................................................     25
24. RELOCATION ..........................................................     25
25. HOLDING OVER ........................................................     25
26. SUBORDINATION TO MORTGAGES; ESTOPPEL CERTIFICATE ....................     26
27. ATTORNEYS' FEES .....................................................     26
28. NOTICES .............................................................     26
29. EXCEPTED RIGHTS .....................................................     27
30. SURRENDER OF PREMISES ...............................................     27
31. PARKING .............................................................     27
32. ENVIRONMENTAL MATTERS/HAZARDOUS MATERIALS ...........................     27
33. MISCELLANEOUS .......................................................     30
34. ENTIRE AGREEMENT ....................................................     33
</TABLE>

EXHIBIT A (Outline and Location of Premises and Landlord's Conduits)
EXHIBIT B (INTENTIONALLY OMITTED)
EXHIBIT C (Description of Property)
EXHIBIT D (Rules and Regulations))
EXHIBIT E (Commencement Letter)
EXHIBIT F (Haz Mat Certificate)
EXHIBIT G (Tenant Options)

                                       i
<PAGE>   3
EXHIBIT H (Form of Landlord Consent and Subordination Agreement)

                                       ii
<PAGE>   4
                                 LEASE AGREEMENT

      This Lease ("Lease") is made and entered into as of May 15, 2000, by and
between CARLYLE-CORE CHICAGO LLC, a Delaware limited liability company
("Landlord") and NET2000 COMMUNICATIONS, INC., a Delaware corporation
("Tenant").

1.    BASIC LEASE INFORMATION.

      (a)   "Building" shall mean the building located at 350 East Cermak Road,
            Chicago, Illinois 60616.

      (b)   "Rentable Square Footage of the Building" is estimated to be
            approximately 1,090,000 rentable square feet, subject to Landlord's
            Confirmation (defined below).

      (c)   "Premises" shall mean the area shown on EXHIBIT A to this Lease. The
            Premises are located on the second (2nd) floor of the Building. The
            "Rentable Square Footage of the Premises" is estimated to be
            approximately 25,000 rentable square feet. If the Premises include
            one or more floors in their entirety, all corridors, elevator
            lobbies and restroom facilities located on such full floor(s) shall
            be considered part of the Premises. Landlord and Tenant stipulate
            and agree that the Rentable Square Footage of the Premises, the
            Rentable Square Footage of the Equipment Space and the Rentable
            Square Footage of the Building as stated herein are estimates,
            subject to final measurement by Landlord ("Landlord's
            Confirmation"). Such measurement shall be performed in accordance
            with ANSI/BOMA Z65.1-1996 ("BOMA Standard"). As used herein "Usable
            Area", "Usable Square Feet", "Rentable Square Feet", "Rentable Area"
            and/or "Rentable Square Footage" shall be the amounts determined by
            Landlord, based upon calculation of usable areas and rentable areas
            in accordance with the BOMA Standard, as a result of Landlord's
            Confirmation. Following Landlord's Confirmation (i) Landlord shall
            deliver a copy of Landlord's Confirmation to Tenant for Tenant's
            review and confirmation, and (ii) Landlord will set forth the final
            confirmed measurements in a Commencement Letter in the form of
            Exhibit E attached hereto.

      (d)   "Equipment Space" shall mean the Rooftop Space, Generator Space and
            Electrical Space (as described in Article 6 herein). The Rentable
            Square Footage of the Equipment Space is estimated to be
            approximately 3,400 Rentable Square Feet (assuming 300 Rentable
            Square Feet of Electrical Space), subject to Landlord's
            Confirmation.

      (e)   "Base Rent":

<TABLE>
<CAPTION>
                                   PERIOD
                               (FOLLOWING RENT           ANNUAL RATE
                              COMMENCEMENT DATE)       PER SQUARE FOOT
                              ------------------       ---------------
<S>                           <C>                      <C>
                                   Year 1                  $26.50
                                   Year 2                  $27.30
                                   Year 3                  $28.11
                                   Year 4                  $28.96
                                   Year 5                  $29.83
                                   Year 6                  $30.72
                                   Year 7                  $31.64
                                   Year 8                  $32.59
                                   Year 9                  $33.57
                                   Year 10                 $34.58
                                   Year 11                 $35.61
                                   Year 12                 $36.68
                                   Year 13                 $37.78
                                   Year 14                 $38.92
                                   Year 15                 $40.08
</TABLE>
<PAGE>   5
      (f)   "Equipment Space Rent":

<TABLE>
<CAPTION>
                              PERIOD
                          (FOLLOWING RENT            ANNUAL RATE
                        COMMENCEMENT DATE)         PER SQUARE FOOT
                        ------------------         ---------------
<S>                     <C>                        <C>
                              Year 1                   $26.50
                              Year 2                   $27.30
                              Year 3                   $28.11
                              Year 4                   $28.96
                              Year 5                   $29.83
                              Year 6                   $30.72
                              Year 7                   $31.64
                              Year 8                   $32.59
                              Year 9                   $33.57
                              Year 10                  $34.58
                              Year 11                  $35.61
                              Year 12                  $36.68
                              Year 13                  $37.78
                              Year 14                  $38.92
                              Year 15                  $40.08
</TABLE>

      (g)   "Tenant's Pro Rata Share": The ratio (expressed as a percentage)
            that the Rentable Area of the Premises and the Equipment Space
            located within the Building (if applicable) bears to the Rentable
            Area of the Building; said amount to be determined by Landlord's
            Confirmation.

      (h)   "Commencement Date": The date of mutual execution and delivery of
            this Lease.

      (i)   "Rent Commencement Date": The later to occur of (i) the date that is
            four (4) months from the Commencement Date and (ii) the date upon
            which a certificate of occupancy, temporary or conditional
            certificate of occupancy or other applicable approval or sign-off as
            may be necessary for the legal occupancy of the Building has been
            issued by the appropriate authority.

      (j)   "Term": A period commencing on the Commencement Date and expiring on
            the date ("Expiration Date") that is fifteen (15) years from the
            Rent Commencement Date.

      (k)   "Security Deposit": $188,150.01.

      (1)   "Guarantor(s)": None.

      (m)   "Broker(s)": Core Location Realty Associates of Chicago, LLC,
            representing Landlord and Insignia/ESG, representing Tenant.

      (n)   "Permitted Use": (i) installation, operation and maintenance and
            repair and/or replacement of internet or telecommunications and
            transmission equipment and facilities, including without limitation
            local and long distance switch, node and Co-location (as defined in
            Article 11) and webhosting, subject to the limitations set forth in
            this Lease, as the primary use, and (ii) the storage of tools, parts
            and replacement equipment and (iii) associated general office use
            required to support, monitor and maintain use described in clause
            (i) above.

                                        2
<PAGE>   6
      (o)   "Notice Addresses":

            Tenant:

            Net2000 Communications, Inc.
            2180 Fox Mill Road
            Herndon, Virginia 20171
            Attention: Legal Department

            With a copy to:

            Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
            One Financial Center
            Boston, Massachusetts 02111
            Attention: Daniel O. Gaquin, Esq.

            Landlord:

            CARLYLE-CORE CHICAGO LLC
            c/o Core Location Realty Associates of Chicago, LLC
            4520 East-West Highway, Suite 650
            Bethesda, Maryland 20814
            Attention: Mark Ezra

            With a copy to:

            Shartsis, Friese & Ginsburg LLP
            One Maritime Plaza, 18th Floor
            San Francisco, California 94111
            Attention: Jonathan M. Kennedy, Esq.

            and

            The Carlyle Group
            1001 Pennsylvania Avenue
            Suite 220 South
            Washington, DC 20004
            Attention: Gary Block

      (p)   "Rent Payment Address":

            CARLYLE-CORE CHICAGO LLC
            c/o Core Location Realty Associates of Chicago, LLC
            4520 East-West Highway, Suite 650
            Bethesda, Maryland 20814
            Attention: Management Agent

      (q)   "Business Day(s)" are Monday through Friday of each week, exclusive
            of New Year's Day, Memorial Day, Independence Day, Labor Day,
            Thanksgiving Day and Christmas Day and any other union-recognized
            holidays ("Holidays"). Landlord may reasonably designate additional
            Holidays if such days are holidays recognized by the State of
            Illinois and/or the federal government.

      (r)   "Landlord Work" shall mean the delivery of the Premises and
            Equipment Space in broom clean condition and free of Hazardous
            Materials (defined in Article 32 below) in violation of
            Environmental

                                        3
<PAGE>   7
            Laws (defined in Article 32 below), with the following work
            completed substantially in accordance with the base Building plans:

            (i)   plumbing risers installed;

            (ii)  sprinkler system consisting of horizontal and branch piping
                  distributed from a vertical riser system (Landlord shall
                  provide the contacts on the Building fire alarm panel which is
                  located on the 1st floor);

            (iii) the core side of the common area corridors (Tenant is
                  responsible for Tenant's side) demised with drywall meeting
                  all applicable codes;

            (iv)  communications risers capable of handling fiber optic voice
                  and data lines; and

            (v)   bathrooms, core doors (as required for the base Building as
                  opposed to the Premises) and elevator recall buttons to be
                  delivered in compliance with Americans Disabilities Act and
                  other applicable laws.

      (s)   "Law(s)" means all applicable statutes, codes, ordinances, orders,
            rules and regulations of any municipal or governmental entity.

      (t)   "Property" means the Building, the parking lot serving the Building
            and the parcel(s) of land on which they are located and, at
            Landlord's discretion, other improvements serving the Building, if
            any, and the parcel(s) of land on which they are located. The
            Property is generally described in EXHIBIT C attached hereto,
            provided the parties acknowledge that the Property is subject to
            change, by addition, reduction or improvement thereon, from time to
            time.

2.    LEASE GRANT.

      (a)   Premises. Landlord leases the Premises to Tenant and Tenant leases
            the Premises from Landlord, together with the right in common with
            others to use any portions of the Property that are designated by
            Landlord for the common use of tenants and others, such as
            sidewalks, unreserved parking areas, common corridors, elevator
            foyers, restrooms, vending areas and lobby areas (the "Common
            Areas"). Landlord currently intends to provide access to the shared
            conference room within the Building to tenants and, for so long as
            such conference room is made available (Landlord has no present
            intention to terminate the availability of the conference room),
            Tenant shall have the right, in common with the other tenants, to
            use such facility.

      (b)   Equipment Space. Additionally, pursuant to the provisions of Article
            6 below, Tenant shall have the exclusive right to place certain
            equipment in the Equipment Space.

3.    TERM; POSSESSION.

      The Term shall commence on the Commencement Date and shall expire, if not
      sooner terminated pursuant to the provisions of this Lease, on the
      Expiration Date. On the Commencement Date, the Premises and Equipment
      Space are accepted by Tenant in "as is" condition and configuration,
      subject to Landlord's maintenance and repair obligations set forth in this
      Lease. By taking possession of the Premises and Equipment Space, Tenant
      agrees that the Premises and Equipment Space are in good order and
      satisfactory condition, and that there are no representations or
      warranties by Landlord regarding the condition of the Premises, Equipment
      Space or the Building except as may be expressly set forth herein. If
      Landlord is delayed in delivering possession of the Premises and
      Equipment Space or any other space, Landlord shall use reasonable efforts
      to obtain possession of the space, but no such delay shall nullify this
      Lease or give rise to any claim for damages on the part of Tenant. If
      Tenant takes possession of the Premises or Equipment Space before the
      Commencement Date, such possession shall be subject to the

                                        4
<PAGE>   8
      terms and conditions of this Lease except that, prior to the Rent
      Commencement Date, Tenant will not be required to pay Rent hereunder.

4.    RENT.

      (a)   Payments. As consideration for this Lease, Tenant shall pay Landlord
            at the Rent Payment Address (or such other address as Landlord may
            from time to time specify in writing as the Rent Payment Address),
            without any setoff or deduction (except as expressly provided in
            this Lease), the total amount of Base Rent, Equipment Space Rent and
            Additional Rent due for the Term, commencing as of the Rent
            Commencement Date. "Additional Rent" means all sums (exclusive of
            Base Rent and Equipment Space Rent) that Tenant is required to pay
            Landlord. Additional Rent, Base Rent and Equipment Space Rent are
            sometimes collectively referred to as "Rent". Tenant shall pay and
            be liable for all rental, sales and use taxes (but excluding income
            taxes), if any, imposed upon or measured by Rent under applicable
            Law. Base Rent, Equipment Space Rent and recurring monthly charges
            of Additional Rent shall be due and payable in advance on the first
            day of each calendar month without notice or demand, provided that
            the installment of Base Rent and Equipment Space Rent (based upon
            the estimated Rentable Area of the Premises and Equipment Space
            described in Sections 1(c) and 1(d) above) for the first full
            calendar month following the Rent Commencement Date shall be payable
            upon the execution of this Lease by Tenant. All other items of Rent
            shall be due and payable by Tenant on or before thirty (30) days
            after billing by Landlord. All payments of Rent shall be by good and
            sufficient check or by other means (such as automatic debit or
            electronic transfer) acceptable to Landlord. If Tenant fails to pay
            any item or installment of Rent when due, Tenant shall pay Landlord
            an administration fee equal to five percent (5%) of the past due
            Rent. If the Term commences on a day other than the first day of a
            calendar month or terminates on a day other than the last day of a
            calendar month, the Rent for the month shall be prorated based on
            the number of days in such calendar month. Landlord's acceptance of
            less than the correct amount of Rent shall be considered a payment
            on account of the earliest Rent due. No endorsement or statement on
            a check or letter accompanying a check or payment shall be
            considered an accord and satisfaction, and Landlord may accept the
            check or payment without prejudice to Landlord's right to recover
            the balance or pursue other available remedies. Except as expressly
            provided herein, Tenant's covenant to pay Rent is independent of
            every other covenant in this Lease.

      (b)   Payment of Tenant's Pro Rata Share of Operating Expenses and
            Property Taxes.

            (i)   Generally. Commencing as of the Rent Commencement Date,
                  Tenant shall pay as Additional Rent, Tenant's Pro Rata Share
                  of the total amount of Operating Expenses (defined below) and
                  Property Taxes (defined below) for each calendar year during
                  the Term. Landlord shall provide Tenant with a good faith
                  estimate of the total amount of Operating Expenses and
                  Property Taxes for each calendar year during the Term. On or
                  before the first day of each month, Tenant shall pay to
                  Landlord a monthly installment equal to one-twelfth of
                  Tenant's Pro Rata Share of Landlord's estimate of the total
                  amount of Operating Expenses and Property Taxes. If Landlord
                  determines that its estimate was incorrect, Landlord may
                  provide Tenant with a revised estimate. After its receipt of
                  the revised estimate, Tenant's monthly payments shall be based
                  upon the revised estimate. If Landlord does not provide Tenant
                  with an estimate of the total amount of Operating Expenses and
                  Property Taxes by January 1 of a calendar year, Tenant shall
                  continue to pay monthly installments based on the previous
                  year's estimate until Landlord provides Tenant with the new
                  estimate. Upon delivery of the new estimate, an adjustment
                  shall be made for any month for which Tenant paid monthly
                  installments based on the previous year's estimate. Tenant
                  shall pay Landlord the amount of any underpayment within
                  thirty (30) days after receipt of the new estimate. Any
                  overpayment shall be refunded to Tenant within thirty (30)
                  days or credited against the next due future installment(s) of
                  Additional Rent.

                                        5
<PAGE>   9
            (ii)  Reconciliation Statement. As soon as is reasonably practical
                  following the end of each calendar year, Landlord shall
                  furnish Tenant with a statement ("Reconciliation Statement")
                  of the actual amount of Operating Expenses and Property Taxes
                  for the prior calendar year and Tenant's Pro Rata Share of
                  same. If the amount of Operating Expenses and Property Taxes
                  actually paid by Tenant for the prior calendar year is more
                  than the actual amount of Operating Expenses and Property
                  Taxes for the prior calendar year, Landlord shall apply any
                  overpayment by Tenant against Additional Rent due or refund
                  such amount within thirty (30) days after the Reconciliation
                  Statement is provided to Tenant, provided if the Term expires
                  before the determination of the overpayment, Landlord shall
                  refund any overpayment to Tenant after first deducting the
                  amount of Rent due, if any. If the amount of Operating
                  Expenses and Property Taxes paid by Tenant for the prior
                  calendar year is less than the actual amount of Operating
                  Expenses and Property Taxes for such prior year, Tenant shall
                  pay Landlord, within thirty (30) days after its receipt of the
                  Reconciliation Statement of Operating Expenses and Property
                  Taxes, any underpayment for the prior calendar year. The
                  obligations of Landlord and Tenant under this Section 4(b)
                  shall survive the expiration or sooner termination of the
                  Term.

            (iii) Audit.

                  (A)   Provided that Tenant is not in default under this Lease
                        (beyond any applicable notice and cure periods) as of
                        the date of Tenant's exercise of its audit rights,
                        within ninety (90) days after receipt of a
                        Reconciliation Statement ("Audit Period"), Tenant shall
                        be entitled, upon at least ten (10) Business Days prior
                        written notice to Landlord and during normal business
                        hours at Landlord's office, or such other place as
                        Landlord shall designate, to cause a certified public
                        accountant ("CPA") to copy (at Tenant's expense),
                        inspect, examine and audit those books and records of
                        Landlord relating to the determination of Operating
                        Expenses and Property Taxes for the calendar year for
                        which such statement was prepared. The initial
                        inspection of Landlord's records may be conducted by a
                        current employee of Tenant, a recognized regional or
                        national accounting firm (but not a tenant of the
                        Property) or such other person designated by Tenant and
                        reasonably acceptable to Landlord. In connection
                        therewith, Tenant acknowledges that it shall be
                        reasonable for Landlord to object to the proposed use by
                        Tenant of any persons engaged in the business of
                        auditing Landlord's books and records on a contingent
                        fee basis.

                  (B)   If, after inspection and examination of such books and
                        records during the Audit Period, Tenant disputes the
                        amount of Operating Expenses or Property Taxes charged
                        by Landlord, Tenant shall have ten (10) Business Days
                        following the date of completion of Tenant's audit
                        ("Request Period") to request an independent audit of
                        such books and records, such request to be made by
                        written notice to Landlord ("Audit Request"), which
                        notice shall specify with particularity all disputed
                        items and shall contain a true, correct and complete
                        copy of any report or summary prepared by Tenant's
                        initial auditor. The independent audit of the books and
                        records shall be conducted by a CPA acceptable to both
                        Landlord and Tenant. If, within ten (10) days after
                        Landlord's receipt of Tenant's notice requesting an
                        audit, Landlord and Tenant are unable to agree on the
                        CPA to conduct such audit, then Landlord shall designate
                        a nationally recognized accounting firm (other than
                        Landlord's then current accounting firm) to conduct such
                        audit. The audit shall be limited to the determination
                        of the proper amount of Operating Expenses and Property
                        Taxes payable by Tenant specified by Tenant as disputed
                        items in Tenant's Audit Request.

                  (C)   If the audit discloses that the amount of such disputed
                        Operating Expenses and/or Property Taxes billed to
                        Tenant was incorrect, the appropriate party shall,
                        within

                                        6
<PAGE>   10
                        thirty (30) days following the date of such
                        determination, pay to the other party the deficiency or
                        overpayment, as applicable. All costs and expenses of
                        any audit shall be paid by Tenant unless the audit shows
                        that Landlord overstated Operating Expenses and Property
                        Taxes for the subject calendar year by more than five
                        percent (5%), in which case Landlord shall pay all costs
                        and expenses of the audit.

                  (D)   Tenant shall keep any information gained from any such
                        audit (including Tenant's initial review of Landlord's
                        books and records) confidential and shall not disclose,
                        or allow the disclosure of, any such information to any
                        other party except where Tenant is legally required to
                        do so (or in the case of litigation or where such
                        disclosure occurs as part of litigation between Landlord
                        and Tenant), and shall indemnify, defend, protect and
                        hold Landlord harmless from and against any and all
                        loss, cost, damage or liability incurred by Landlord
                        arising out of Tenant's (or Tenant's accountants',
                        consultants' or employees') failure to maintain such
                        confidentiality.

                  (E)   The exercise by Tenant of any audit rights hereunder
                        shall not relieve Tenant of its obligation to pay,
                        prior to the request for an inspection and examination
                        of Landlord's books and records or any audit, all sums
                        due hereunder, including, without limitation, any
                        disputed Operating Expenses and/or Property Taxes. If
                        Tenant does not elect to exercise its rights to audit
                        during the Audit Period, or does not elect to cause an
                        independent audit of the books and records during the
                        Request Period, then Landlord's Reconciliation Statement
                        shall conclusively be deemed to be correct, and Tenant
                        shall be bound by Landlord's determination.

      (c)   Operating Expenses Defined. "Operating Expenses" means all costs and
            expenses incurred in each calendar year in connection with the
            operation, ownership, management, maintenance and repair of the
            Building and the Property, including, but not limited to:

            (i)   Labor costs, including, wages, salaries, social security and
                  employment taxes, medical and other types of insurance,
                  uniforms, training, and retirement and pension plans (provided
                  that if any such individuals perform work for multiple
                  properties, the associated labor costs will be equitably
                  prorated by Landlord).

            (ii)  Management fees payable either to Landlord (if Landlord
                  manages the Building and Property) or to a third party, as
                  well as the cost, including rent or imputed rent of equipping
                  and maintaining a management office (if applicable),
                  accounting and bookkeeping services, legal fees not
                  attributable to leasing or collection activity, and other
                  administrative costs.

            (iii) The cost of services, including amounts paid to service
                  providers and the rental and purchase cost of parts, supplies,
                  tools and equipment.

            (iv)  Premiums and deductibles paid by Landlord for insurance,
                  including workers compensation, fire and extended coverage,
                  earthquake, general liability, rental loss, elevator, boiler
                  and other insurance customarily carried from time to time by
                  owners of comparable buildings.

            (v)   Costs of electricity and charges for water, gas, steam and
                  sewer and other utilities, but excluding (a) those charges for
                  which Landlord is reimbursed by tenants and (b) the cost of
                  electricity provided to any tenant who is billed directly by
                  the applicable utility provider for the cost of such tenant's
                  electricity consumption.

            (vi)  The amortized cost of capital improvements made to the
                  Property which are: (A) performed primarily to reduce
                  operating expense costs or otherwise improve the operating
                  efficiency of the Property, (B) required to comply with any
                  Laws that are enacted, or first interpreted to

                                       7
<PAGE>   11
                  apply to the Property, after the date of this Lease, or (C)
                  replacements of existing capital improvements or equipment.
                  The cost of capital improvements, together with interest,
                  shall be amortized by Landlord over such reasonable period as
                  Landlord may determine.

      (d)   Exclusions to Operating Expenses. Operating Expenses do not include:

            (i)     the cost of capital improvements (except as set forth
                    above);

            (ii)    depreciation;

            (iii)   interest (except as provided above for the amortization of
                    capital improvements);

            (iv)    principal payments of mortgage and other non-operating debts
                    of Landlord;

            (v)     the cost of repairs or other work to the extent Landlord is
                    reimbursed by insurance or condemnation proceeds or any
                    third parties (including direct payment by tenants);

            (vi)    the cost of leasing space in the Building, including
                    brokerage commissions and so-called "take-over" or "buy-out"
                    obligations;

            (vii)   costs incurred in connection with the sale, financing or
                    refinancing of the Building;

            (viii)  organizational expenses associated with the creation and
                    operation of the entity which constitutes Landlord;

            (ix)    costs of remediation of Hazardous Materials existing in the
                    Building or the Property;

            (x)     costs incurred in connection with the construction,
                    expansion or renovation of the Building;

            (xi)    fines or penalties assessed against Landlord or the Building
                    or Property due to the Building's or Property's violation of
                    or failure to comply with any applicable Laws as existing
                    and enforced as of the date of this Lease;

            (xii)   advertising or promotional expenditures for the Building;

            (xiii)  amounts paid to entities related to Landlord to the extent
                    the same are materially in excess of the cost of such
                    services which would have been paid had such services been
                    procured from a competitive source;

            (xiv)   interest, late charges or penalties incurred as a result of
                    Landlord's failure to pay bills in a timely manner;

            (xv)    reserves for anticipated future expenses or reserves for bad
                    debt loss;

            (xvi)   legal and other professional fees not related to the
                    operation of the Property;

            (xvii)  the cost of providing improvements within the Premises (as
                    opposed to the repairs and maintenance) of any other tenants
                    in the Building or Property;

            (xviii) rent payable under any ground or superior lease encumbering
                    the Building and/or Property;

            (xix)   amounts paid by Landlord under any indemnity obligation set
                    forth in a lease for space in the Building;

                                       8

<PAGE>   12
            (xx)    rentals and other related expenses incurred in leasing air
                    conditioning systems, elevators or other equipment, the cost
                    of which, if purchased, would pursuant to the provisions set
                    forth above, be excluded from Operating Expenses as a
                    capital cost, except equipment not affixed to the Building
                    which is used in providing janitorial or similar services
                    and, further excepting from this exclusion such equipment
                    rented or leased to remedy or ameliorate an emergency
                    condition in the Property;

            (xxi)   costs, other than those incurred in ordinary maintenance and
                    repair, for "museum or exhibition quality" sculpture,
                    paintings, fountains or other objects of art; and

            (xxii)  cost arising from Landlord's charitable or political
                    contributions.

      (e)   Property Taxes Defined. "Property Taxes" shall mean: (1) all real
            estate taxes and other assessments on the Building and/or Property,
            including, but not limited to, assessments for special improvement
            districts and building improvement districts, taxes and assessments
            levied in substitution or supplementation in whole or in part of any
            such taxes and assessments and the Property's share of any real
            estate taxes and assessments under any reciprocal easement
            agreement, common area agreement or similar agreement as to the
            Property; (2) all personal property taxes for property that is owned
            by Landlord and used in connection with the operation, maintenance
            and repair of the Property; and (3) all reasonable costs and fees
            incurred in connection with seeking reductions in any tax
            liabilities described in (1) and (2), including, without limitation,
            any costs incurred by Landlord for compliance, review and appeal of
            tax liabilities. Notwithstanding the foregoing, Property Taxes shall
            not include any income, capital levy, capital stock, gift, estate or
            inheritance tax, unless imposed as a replacement for, or in lieu of
            Property Taxes. Whenever reasonably possible, any special assessment
            included in Property Taxes shall be treated as if paid in the
            maximum number of installments permissible.

      (f)   Gross Up. If the Building is not at least one hundred percent (100%)
            occupied or fully tax assessed during any calendar year, Operating
            Expenses and Property Taxes shall be determined as if the Building
            had been one hundred percent (100%) occupied and fully taxed
            assessed during that calendar year. In addition, if any particular
            work or service otherwise included in Operating Expenses is not
            furnished to a tenant or occupant of the Building who is undertaking
            to perform such work or service itself, Operating Expenses shall be
            deemed to be increased by an amount equal to the additional
            Operating Expenses which would have incurred if Landlord had
            furnished such work to such tenant or occupant.

5.    COMPLIANCE WITH LAWS; USE.

      (a)   Generally. The Premises shall be used only for the Permitted Use and
            for no other use whatsoever. The Equipment Space shall be used only
            for the uses described in Article 6 below. Tenant shall not use or
            permit the use of the Premises or Equipment Space for any purpose
            which is illegal, dangerous to persons or property or which, in
            Landlord's reasonable opinion, unreasonably disturbs or interferes
            with the operations of any other tenants of the Building or in any
            way interferes with the operation of the Building. Any equipment to
            be installed within the Building, Premises or Equipment Space by
            Tenant that, in Landlord's reasonable determination, may cause
            unsafe (in Landlord's reasonable determination) vibrations which may
            be transmitted to the structure of the Building or unreasonable
            levels of noise shall be installed and maintained by Tenant, at
            Tenant's sole cost and expense, in such a manner as Landlord may
            determine to be necessary in order to eliminate such vibration or
            noise. Tenant shall comply with all Laws, including the Americans
            with Disabilities Act, regarding the operation of Tenant's business
            and the use, condition, configuration and occupancy of the Premises
            and Equipment Space except that Tenant shall not be responsible
            insofar as such Laws (i) pertain to the Building's structure, it
            being Landlord's general obligation to maintain the Building's
            structure and Common Areas in compliance with applicable Laws
            (unless the application of such Laws are due to its work performed
            by or on behalf of a tenant's particular use of or actions

                                       9

<PAGE>   13
            within the premises or equipment spaces), or (ii) are applicable
            with respect to tenants in the Building in general as opposed to
            Tenant's particular use and occupancy. Tenant shall comply with the
            rules and regulations of the Building attached as EXHIBIT D and such
            other reasonable rules and regulations adopted by Landlord from time
            to time promptly following notice by Landlord of the adoption of
            such rules and regulations. Tenant shall also cause its agents,
            contractors, subcontractors, employees, customers, and subtenants to
            comply with all rules and regulations. Landlord agrees to enforce
            the rules and regulations uniformly with respect to all tenants in
            the Building.

      (b)   Labor Relations. Tenant shall not take any action which would
            violate Landlord's labor contracts or which would cause a work
            stoppage, picketing, labor disruption or dispute, or unreasonably
            interfere with Landlord's or any other tenant's or occupant's
            business or with the rights and privileges of any person lawfully in
            the Building ("Labor Disruption"). Tenant shall take the reasonable
            actions necessary to resolve the Labor Disruption, and shall have
            pickets removed and, at the reasonable request of Landlord,
            immediately terminate any work in the Premises that gave rise to the
            Labor Disruption, until Landlord gives its written consent for the
            work to resume, which consent shall not be unreasonably withheld,
            delayed or conditioned. Tenant shall have no claim for damages
            against Landlord or any of the Landlord Related Parties, nor shall
            the Commencement Date be extended as a result of the above actions.

      (c)   Riser Use. Tenant, at Tenant's sole cost and expense, shall have the
            right in common with other tenants in the Building to install
            Tenant's conduit (said conduits and the contents thereof being
            referred to herein as "Cable") in the Building's horizontal and
            vertical pathways, risers and ducts ("Risers") in an amount not to
            exceed the following:

            (i)   A total of four (4) 4" conduits for the purposes of routing
                  Tenant's fiber to the Premises from two (2) of the Building's
                  fiber vaults (2 in each riser) located in the lower level of
                  the Building as designated by Landlord; and

            (ii)  One (1) 4" conduit for the purposes of routing Tenant's fiber
                  from the Premises to the Building meet-me room (the "Meet-Me
                  Room") as designated by Landlord.

            (iii) If, at any time during the Term, Landlord, in Landlord's sole
                  discretion, elects to make additional Riser capacity available
                  to tenants of the Property for the purpose of routing
                  additional fiber, Landlord agrees that Tenant shall be
                  afforded the right to elect to utilize, at Tenant's sole cost
                  and expense, its equitable portion of such additional Riser
                  capacity as reasonably determined by Landlord, on the terms
                  (including any fees or charges) Landlord is then granting to
                  tenants in general. If Tenant does not elect to use such
                  additional capacity, Landlord shall not be obligated to
                  reserve such additional capacity for Tenant, but may
                  thereafter, in Landlord's sole discretion, allow other parties
                  to use the additional Riser capacity that was made available
                  to Tenant.

All such work of installation will be carried out in compliance with Article 8
below; provided that all work within the Risers shall be performed by a
contractor specified by Landlord or chosen from Landlord's list of approved
contractors. Tenant will reimburse Landlord within thirty (30) days after demand
for any costs incurred by Landlord in assisting Tenant with said conduits. In
connection with Tenant's Riser use, Landlord shall permit Tenant, at Tenant's
sole cost and expense, to connect to Tenant's telecommunication providers,
provided however that such providers shall (i) follow the Building's standard
procedures for such connectivity, and (ii) utilize Tenant's allotment of Risers
to bring such service to Tenant. Landlord shall not limit Tenant in its choice
of fiber providers. With respect to Tenant's rights to use the Meet-Me Room,
Tenant expressly acknowledges that Landlord will be entitled to charge a fee for
such usage to all occupants of the Building making use of the Meet-Me Room, such
charge to be reasonably determined by Landlord in order to provide an equitable
allocation of the cost of operation of the Meet-Me Room among those tenants
which use the Meet-Me Room.

                                       10

<PAGE>   14
6.    EQUIPMENT SPACE.

      Tenant shall have the right to use the Equipment Space as follows:

      (a)   Equipment Space Generally. Tenant, at Tenant's sole cost and
            expense, may

            (i)   use up to:

                  (A)   if Tenant does not contract with Trigen for the
                        provision of Tenant's cooling requirements pursuant to
                        Section 7(a)(vii) below, a total of 2,400 Rentable
                        Square Feet of space on the Building roof and Building
                        penthouse in the areas in a location and configuration
                        to be designated by Landlord to the extent necessary to
                        install, maintain and operate Tenant's supplemental air
                        conditioning equipment; and

                  (B)   a total of four (4) Rentable Square Feet of space on the
                        Building roof in a location and configuration to be
                        designated by Landlord, for the installation and
                        operation of GPS systems and communications equipment
                        (if Tenant does not contract with Trigen, said four (4)
                        Rentable Square Feet will be included in the Rentable
                        Square Feet described in Section 6(a)(i)(A) above);

                  The equipment to be installed on the Building rooftop pursuant
                  to this Section 6(a)(i) being referred to as "Rooftop
                  Equipment" and the area utilized by such Rooftop Equipment is
                  referred to as "Rooftop Space").

            (ii)  use up to 700 Rentable Square Feet of space in the Building in
                  an area to be designated by Landlord for the purposes of
                  installing and maintaining, one (1) generator not larger than
                  1500 KW, as well as an area to be located underground outside
                  of the Building in a location and configuration to be
                  designated by Landlord to accommodate up to a 2,000 gallon
                  fuel storage tank (such generator and tank being collectively
                  referred to herein as "Generator"). Tenant shall be required
                  to route all electrical distribution from the Generator to the
                  Electrical Space (as defined below) (the areas required for
                  the Generator are referred to as the "Generator Space").

            (iii) use a reasonable quantity of space as required by Tenant's
                  electrical equipment necessary to supply Tenant's electrical
                  service as provided for in the first (1st) sentence of Section
                  7(a)(iv) below ("Electrical Equipment") in the lower level of
                  the Building ("Electrical Space") in a location and
                  configuration to be designated by Landlord for Tenant's
                  Electrical Equipment.

The Rooftop Equipment, Generator and Electrical Equipment are collectively
herein referred to as "Site Equipment". As described in Article 1, the area of
the Equipment Space shall be determined by Landlord upon the final designation
of the location of the Equipment Space, and the area of the Equipment Space (as
well as the Equipment Space Rent payable hereunder) will be confirmed by the
parties in the Commencement Letter issued by Landlord. At any time after the
24th month following the Commencement Date, Landlord may, by written notice to
Tenant, reduce the Equipment Space by removing therefrom any Equipment Space
which Tenant has not, as of the date of Landlord's notice, used. If Landlord so
elects to reduce the Equipment Space, the Equipment Space Rent shall be adjusted
accordingly. The exact location and configuration of Tenant's Site Equipment is
subject to Landlord's approval, in accordance with Article 8, and the Site
Equipment shall be installed in locations and configurations which, in
Landlord's reasonable opinion, may be used by Landlord or other tenants if
Landlord elected to reduce the Equipment Space as provided for above. Tenant
acknowledges that the efficient layout and configuration of Building occupants'
equipment is a material consideration to Landlord and the operation of the
Property as a whole, and that without Tenant's agreement to configure and locate
Tenant's Site Equipment as requested by Landlord, Landlord

                                       11

<PAGE>   15
would potentially be unable to provide sufficient equipment space for all
Building occupants and would not be willing to enter into this Lease.

      (b)   [INTENTIONALLY OMITTED]

      (c)   Equipment Space Interference. If, any electrical, electromagnetic,
            radio frequency or other interference of equipment existing prior to
            Tenant's installation shall result from the operation of any Site
            Equipment located in the Equipment Space, Landlord will notify
            Tenant, and if such interference is not cured within five (5)
            business days following delivery of such notice, Tenant agrees that
            Landlord may, at Landlord's option, shut down Tenant's equipment
            upon eight (8) hours prior notice to Tenant; provided, however, if
            an emergency situation exists, which Landlord reasonably determines
            in its sole discretion to be attributable to Tenant's Site
            Equipment, Landlord shall immediately notify Tenant verbally, who
            shall act immediately to remedy the emergency situation. Should
            Tenant fail to so remedy said emergency situation, Landlord may then
            act to shut down Tenant's equipment. Tenant shall indemnify Landlord
            and hold it harmless from all expenses, costs, damages, losses,
            claims or other liabilities arising out of said shutdown. Tenant
            agrees to cease operations (except for intermittent testing on a
            schedule approved by Landlord) until the interference has been
            corrected to the satisfaction of Landlord. If such interference has
            not been corrected within thirty (30) days, Landlord may, at its
            option, either terminate Tenant's right to use the Equipment Space
            forthwith, or require that Tenant immediately remove the specific
            item of Site Equipment causing such interference. Landlord will use
            reasonable efforts to include a provision substantially similar to
            this Section 6(c) in other leases affecting the Building.

      (d)   Generator Use. Tenant agrees that Tenant will only run the Generator
            during emergency circumstances related to the loss of primary
            commercial power and during customary testing hours as determined by
            Landlord in its sole discretion and as required by Tenant (with
            notice to Landlord) to meet the Generator manufacturer's warranty.

      (e)   Subleasing/Use by Third Parties. Except in connection with a
            Permitted Transfer or Co-location (in either of which event the
            consent of Landlord shall not be required), Tenant shall not be
            permitted to sublicense, license or share its Equipment Space with
            third parties without the prior written consent of Landlord, which
            consent Landlord may withhold in its sole discretion. In addition,
            Tenant shall not use the Rooftop Space to enable other providers of
            Communications Services (defined below) to provide Communications
            Services to any tenant, occupant or licensee of the Building or to
            any tenant, occupant or licensee of any other building. Tenant may
            not allow any other provider of telecommunications, video, data or
            related services ("Communications Services") to locate any equipment
            in the Rooftop Space for any purpose whatsoever.

7.    SERVICES.

      (a)   Landlord's Obligation. Landlord will provide the following services,
            subject to the recovery of the cost of same as Operating Expenses,
            except as set forth in Section 7(a)(vii):

            (i)   Water to restrooms in Common Areas;

            (ii)  Janitorial service to the Common Areas in the Building on
                  Business Days. Tenant shall provide, and pay directly for,
                  janitorial services to the Premises pursuant to a janitorial
                  contract with a provider approved by Landlord (such approval
                  not to be unreasonably withheld);

            (iii) Freight and passenger elevator service;

            (iv)  Electricity as follows: Following the Rent Commencement Date,
                  dedicated commercial utility power of approximately 70 watts
                  per square foot of Usable Area of the Premises at 480/277

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<PAGE>   16
                  volts, 3 phase to a utility company service entrance in the
                  Building. Tenant shall be responsible for all costs and
                  expenses required to utilize such power including but not
                  limited to bringing power from service entrance equipment,
                  transient voltage surge suppressors, meter cabinets and
                  distribution system equipment to the Premises and Equipment
                  Space. Service switchgear/switchboards, meter cabinets and
                  paralleling switchgear for Tenant's use will be placed by
                  Tenant, at Tenant's expense, in the Electrical Space.
                  Landlord's obligation to furnish electrical and other utility
                  services shall be subject to the rules and regulations of the
                  supplier of such electricity of other utility services and the
                  rules and regulations of any municipal or other governmental
                  authority regulating the business of providing electricity and
                  other utility services. Notwithstanding the foregoing,
                  Landlord shall at all times be able to shut down the utility
                  services to the Premises or to the Equipment Space in
                  connection with any maintenance operation conducted for the
                  Building. Landlord agrees to use reasonable efforts to
                  cooperate with Tenant in obtaining temporary alternative power
                  during scheduled maintenance operations, but shall have no
                  obligation hereunder to provide alternative power from
                  emergency power sources. Prior to shutting down any electrical
                  power servicing Tenant's Site Equipment, Landlord agrees to
                  give Tenant reasonable prior written notice, except in
                  emergency situations. Additionally, if Tenant's requirements
                  for electrical service increase to an amount greater than the
                  amount set forth in the first (1st) sentence of this Section
                  7(a)(iv), Landlord shall cooperate with Tenant in Tenant's
                  efforts to obtain such additional capacity, including but not
                  limited to executing such permit applications as may
                  reasonably be required, provided that Tenant shall pay all
                  costs associated with or arising out of the effort to obtain
                  such permits and additional capacity and the cost of any
                  necessary modifications to the Property to accommodate the
                  provision of such additional electrical service; it is the
                  intent of the parties that in no event will Landlord be
                  required to expend any funds or assume any additional
                  liability with respect to Tenant's efforts to procure
                  additional electrical service.

            (v)   Security Service as follows: manned security 24-hours per day,
                  365 days per year. Landlord shall not be deemed to have
                  warranted the efficiency or efficacy of any security
                  personnel, services, procedures or equipment and Landlord
                  shall not be liable in any manner for the failure of such
                  security personnel, services, procedures or equipment to
                  prevent or control, or apprehend anyone suspected of personal
                  injury, property damage or any criminal conduct in, on or
                  about the Property.

            (vi)  Heating, ventilation and air conditioning in reasonable
                  quantities to Common Areas in the Building.

            (vii) On Tenant's request, to be delivered on or before sixty (60)
                  days following the date of mutual execution and delivery of
                  this Lease, Tenant will have the right to use the base
                  Building chilled water risers ("Chilled Water Risers") to
                  accommodate up to four hundred (400) tons of chilled water
                  capacity. Said chilled water capacity will be provided by
                  Trigen People Energy Company ("Trigen"), an off-site (e.g.,
                  not located on the Property) source, pursuant to a separate
                  agreement between Tenant and Trigen. All such chilled water
                  usage, as well as electrical usage related to the Chilled
                  Water Risers, will be separately metered by Tenant at Tenant's
                  sole cost. Tenant will be directly responsible for all costs
                  associated with the use of such cooling capacity, including
                  without limitation, electricity and water consumption. If
                  possible Tenant shall contract directly with the electrical
                  utility with respect to such electrical consumption (if a
                  separate contract is not feasible, Tenant will reimburse
                  Landlord as Additional Rent for the costs of such electrical
                  consumption). Tenant acknowledges that in order for Landlord
                  to allow Tenant to make such use of the Chilled Water Risers,
                  certain portions of the Chilled Water Risers must be modified,
                  and Tenant shall pay to Landlord, within thirty (30) days
                  following Tenant's exercise of the right to use Trigen, the
                  sum of one hundred twenty dollars ($120.00) per ton of
                  chilled water capacity (i.e., if Tenant uses four hundred
                  (400) tons, the sum of $48,000.00), to defray Landlord's

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<PAGE>   17
                   cost of performing such modifications. Tenant expressly
                   acknowledges that Landlord is not responsible for, and will
                   have absolutely no liability whatsoever regarding the
                   interruption or curtailment of, any such chilled water
                   capacity to be provided by Trigen to Tenant, that Tenant will
                   look only to Trigen in the event of any such interruption or
                   curtailment, and that in no event will any interruption or
                   curtailment of such chilled water capacity give rise to any
                   right on the part of Tenant to an abatement of Rent
                   hereunder.

            (viii) Access. Tenant (as well as Tenant's customers, vendors,
                   contractors, employees and agents, as well as any persons who
                   may use the Premises in accordance with the provisions of
                   Section 11(a) below, as authorized by Tenant) shall have
                   access to the Building, the Premises and the Equipment Space
                   24 hours per day, 365 days per year, subject to Landlord's
                   reasonable guidelines regarding access. Tenant will receive a
                   reasonable allotment of Building card-keys at no charge to
                   Tenant.

      (b)   Utilities Generally. Tenant, at Tenant's sole cost, shall cause
            electricity and other utilities serving the Premises and Equipment
            Space to be separately metered (where possible) and Tenant will pay
            the cost of all consumption and excess utility charges in the
            Premises and/or the Equipment Space directly to the utility
            provider. If, at any time, it is no longer feasible for Tenant to
            contract directly with the utility provider for any services, Tenant
            shall reimburse Landlord, within thirty (30) days following invoice
            therefor, for the cost of the consumption and excess utility charges
            of any such service in the Premises and/or the Equipment Space at
            the same rate paid by Landlord.

      (c)   Interruptions, Failures. No failure to furnish, or any stoppage of,
            any services herein resulting from any cause (including, without
            limitation, any interruption in electrical service or other
            utilities to the Premises and/or Equipment Space) shall make
            Landlord liable in any respect for damages to any person, property
            or business, be construed as an eviction of Tenant, or entitle
            Tenant to any abatement of Rent or other relief from any of Tenant's
            obligations under this Lease. Additionally, Tenant expressly
            acknowledges that Landlord reserves the right from time to time upon
            reasonable advance notice to Tenant (except in the case of
            emergency) to discontinue some or all of the services provided by
            Landlord hereunder if necessary in Landlord's judgment to effect any
            repair or maintenance obligations. Should any malfunction of any
            systems or facilities occur within the Property or should
            maintenance or alterations of such systems or facilities become
            necessary, Landlord shall repair the same promptly and with
            reasonable diligence, and Tenant shall in no event have any claim
            for rebate, abatement of Rent, or damages because of any
            malfunctions in or any interruptions of any service to be provided
            however, regardless of the case. Tenant hereby waives the provisions
            of any applicable existing or future law, ordinance or governmental
            regulation permitting the termination of this Lease due to an
            interruption, failure or inability to provide any services.
            Notwithstanding anything to the contrary contained in this Section
            7(c), if (i) Landlord ceases to furnish any service to be provided
            by Landlord hereunder in the Premises for a period in excess of five
            (5) consecutive days after Tenant notifies Landlord and any
            Mortgagee of such cessation; (ii) such cessation is due to the act
            or omission of Landlord and does not in any way result as a result
            of an act or omission of Tenant or any event of Force Majeure; (iii)
            such cessation is not caused by a fire or other casualty (in which
            case Article 16 shall control); (iv) the restoration of such service
            is reasonably within the control of Landlord; and (v) as a result of
            such cessation, the Premises, or a material portion thereof, is
            rendered untenantable (meaning that Tenant is unable to use the
            Premises in the normal course of its business) and Tenant in fact
            ceases to use the Premises, or material portion thereof, then
            Tenant, as its sole remedy, shall be entitled to receive an
            abatement of Base Rent payable hereunder during the period beginning
            on the sixth (6th) consecutive day of such cessation and ending on
            the day when the service in question has been restored. In the event
            the entire Premises has not been rendered untenantable by the
            cessation in service, the amount of abatement that Tenant is
            entitled to receive shall be prorated based upon the percentage of
            the Premises so rendered untenantable and not used by Tenant.

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<PAGE>   18
8.    ALTERATIONS.

      (a)   Initial Tenant Improvements.

            (i)   Generally. Tenant, upon the full and final execution and
                  delivery of this Lease and all prepaid Rent and the Security
                  Deposit required hereunder, shall have the right to perform
                  initial alterations and improvements in the Premises and the
                  Equipment Space, as well as the installation of Site Equipment
                  and the installation of Cable in the Risers (the "Initial
                  Tenant Improvements"). Tenant will be responsible for the
                  construction of the interior portion of any required demising
                  walls separating the Premises from the remainder of the floor.

            (ii)  Tenant shall be permitted, at Tenant's sole cost and expense,
                  to temporarily place a rubbish container/dumpster in a
                  location to be designated by Landlord during the course of
                  construction of the Initial Tenant Improvements;

            (iii) Tenant, at Tenant's sole cost and expense, shall be permitted
                  to use a crane during the installation of Tenant's equipment,
                  provided that such use shall be in compliance with all
                  applicable Laws, rules, regulations, codes or guidelines and
                  that any such use shall be approved in writing in advance,
                  which approval shall not be unreasonably withheld by Landlord
                  (who shall designate the location of any such crane);

            (iv)  Tenant shall have the right to construct a dry pipe,
                  pre-action system for the Premises, including an independent
                  fire alarm panel and alarm devices and the right, subject to
                  Landlord's prior written approval, to relocate or encase any
                  water main or other water pipes (whether or not related to
                  fire safety) running through the Premises;

            (v)   Provided that the exterior of the Building is not adversely
                  affected, Tenant may install a "thermal break" blocking the
                  windows inside the Premises with one or more drywall
                  partitions;

            (vi)  Tenant may ventilate its supplemental HVAC to the roof per the
                  base Building plans; and

            (vii) Tenant may install its own security system within the Premises
                  as well as a standby battery power system within the Premises.

      (b)   Subsequent Alterations. Tenant shall not make alterations, additions
            or improvements in the Premises, Equipment Space or Risers following
            the completion of the Initial Tenant Improvements (collectively
            referred to as "Alterations") (all improvements to the Premises or
            Equipment Space, as well as Tenant's Cable placed in the Risers,
            including without limitation, the Initial Tenant Improvements and
            any Alterations, are referred to herein as "Leasehold Improvements")
            without first obtaining the written consent of Landlord in each
            instance, which consent shall not be unreasonably withheld, delayed
            or conditioned. Notwithstanding the foregoing, Landlord's consent
            shall not be required for any Alteration that satisfies all of the
            following criteria: 1) is of a cosmetic nature such as painting,
            wallpapering, hanging pictures and installing carpeting; and 2) will
            not affect the systems or structure of the Building and does not
            require work to be performed inside the walls or above the ceiling
            of the Premises; provided that even if consent is not required,
            Tenant shall still comply with all the other provisions of this
            Article 8 (including, without limitation, the obligation to provide
            Landlord with advance notice of any such work). Landlord
            acknowledges that neither the location nor the relocation or
            reconfiguration of any of Tenant's equipment within the Premises
            shall constitute, in and of itself, an Alteration.

      (c)   Procedures. Prior to installing any Leasehold Improvements, Tenant
            shall submit to Landlord for Landlord's approval (which approval
            shall not be unreasonably withheld, delayed or conditioned),

                                       15
<PAGE>   19
            detailed plans and specifications of the planned installation, the
            contractors to be retained by Tenant to perform any Leasehold
            Improvements and further provided that all work in Risers must be
            performed by a contractor selected by Landlord or chosen from
            Landlord's list of approved contractors. Landlord will diligently
            attempt to process and respond to Tenant's requests for approval as
            rapidly as reasonably possible and will use good faith efforts to
            approve or disapprove within ten (10) days of receipt of any request
            for approval. If required due to applicable Law, Landlord will, at
            Tenant's sole cost, assist Tenant in the procurement of Tenant's
            permits for the construction of any Alterations (including, if
            necessary, co-signing applications for permits), provided that it is
            expressly recognized that in no event will Landlord be required to
            expend any funds or assume any additional liability with respect to
            Tenant's efforts to procure permits or approvals necessary for the
            performance of Tenants Alterations. In no, event will Landlord's
            approval of Tenant's plans be deemed a representation that they
            comply with applicable laws, ordinances, rules or regulations or
            that they will not cause interference with other communications
            operations, such responsibility being solely Tenant's. Landlord's
            approval of the general contractor to perform any Leasehold
            Improvements shall not be unreasonably withheld, but will not be
            considered to be unreasonably withheld if any such general
            contractor (i) does not have trade references reasonably acceptable
            to Landlord, (ii) does not maintain insurance (including, without
            limitation, builder's risk insurance) as reasonably required by
            Landlord, (iii) does not have the ability to be bonded for the work
            in an amount of no less than one million dollars ($1,000,000.00),
            (iv) does not provide current financial statements reasonably
            acceptable to Landlord, (v) is not union affiliated or (vi) is not
            licensed as a contractor in the State in which the Building is
            located. The foregoing is not intended to be an exclusive list of
            the reasons why Landlord may reasonably withhold its consent to a
            general contractor. Landlord will have the right to require that
            Tenant procure payment and performance bonds equal to one hundred
            percent (100%) of the contract price in each instance. Prior to
            starting work, Tenant shall furnish Landlord with copies of
            contracts; necessary permits and approvals; evidence of contractors
            and subcontractor's insurance in amounts reasonably required by
            Landlord; and any security for performance that is reasonably
            required by Landlord. Tenant will be responsible to pay for all
            utilities consumed during construction. No such work will commence
            unless and until Tenant has given Landlord all necessary permits and
            approvals and sufficient notice and opportunity to post appropriate
            notices of non-responsibility. Landlord will cooperate with Tenant
            in the listing of such notices so as to facilitate the timely
            construction of Tenant's work. All work shall be constructed in a
            good and workmanlike manner using materials of a quality that is at
            least equal to the quality reasonably designated by Landlord as the
            minimum standard for the Building and shall not unreasonably
            interfere with any work being performed by Landlord or other
            tenants in the Building. Upon completion of any Leasehold
            Improvements, Tenant shall furnish Landlord with: (1) general
            contractor and architect's completion affidavits, (2) full and final
            waivers of lien, (3) receipted bills covering all labor and
            materials expended and used, (4) as-built plans of the Leasehold
            Improvements, and (5) the certification of Tenant and its architect
            that the Leasehold Improvements have been installed in a good and
            workmanlike manner in accordance with the approved plans, and in
            accordance with applicable laws, codes and ordinances. Landlord
            may designate reasonable rules, regulations and procedures for the
            performance of work in the Building and, to the extent reasonably
            necessary to avoid disruption to the occupants of the Building,
            shall have the right to designate the time when any such work may be
            performed. Tenant shall reimburse Landlord within thirty (30) days
            after receipt of an invoice for sums paid by Landlord for third
            party examination of Tenant's plans for any such work. In addition,
            within thirty (30) days after receipt of an invoice from Landlord,
            Tenant shall pay Landlord a fee for Landlord's oversight and
            coordination of any Leasehold Improvements equal to Landlord's cost
            of review of plans and construction supervision. If Landlord
            determines that the Building or the Property has been damaged during
            installation of the Leasehold Improvements, Landlord shall notify
            Tenant and Tenant immediately shall repair the damage. If Tenant
            fails to immediately repair the damage, Tenant shall pay to Landlord
            upon demand the cost, as reasonably determined by Landlord, of
            repairing any damage to the Building or the Property caused by such
            installation.

                                       16
<PAGE>   20
9.    MAINTENANCE.

      (a)   Tenant's Maintenance and Repair Obligations. Tenant, at Tenant's own
            expense, will keep the interior of the Premises, including but not
            limited to all Tenant's Property (defined in Article 14 below), and
            any Equipment Space and Site Equipment, including, without
            limitation, all light fixtures, all mechanical, electrical and
            plumbing facilities and equipment, lamps, fans and any exhaust, fire
            suppression or air conditioning equipment and systems, electrical
            motors and all other appliances and equipment of every kind and
            nature located in the Premises and/or Equipment Space in good order,
            repair and condition at all times during the Term. In addition,
            Tenant, at Tenant's sole cost and expense subject to the prior
            approval of Landlord, and within any reasonable period of time
            specified by Landlord, will promptly and adequately repair all
            damage to the Premises and/or Equipment Space and replace or repair
            all damaged or broken fixtures and appurtenances; provided however,
            that, at Landlord's option, if Tenant fails to make such repairs
            within a reasonable time after written request by Landlord, Landlord
            may, but need not, make such repairs and replacements, and Tenant
            shall pay Landlord the cost thereof upon being billed for same.
            Tenant shall also be responsible for all pest control within the
            Premises and for all trash removal for the Premises.

      (b)   Landlord's Maintenance Obligations. Landlord shall keep in good
            order repair and condition (i) the Common Areas, (ii) the foundation
            and subflooring of the Building and the structural condition of the
            roof, and the exterior walls of the Building (but excluding the
            interior surfaces of exterior walls and the interior and exterior of
            all windows, doors, ceiling and plateglass, which shall be
            maintained and repaired by Tenant), and (iii) the Building's
            elevators.

10.   ENTRY BY LANDLORD

      Landlord, its agents, contractors and representatives may enter the
      Premises to inspect or show the Premises to prospective purchasers,
      lenders or (during the final twelve (12) months of the Term) tenants, to
      make repairs to the Premises, and to conduct or facilitate repairs,
      alterations or additions to any portion of the Building outside of the
      Premises, including other tenants' premises. Except in emergencies,
      Landlord shall provide Tenant with reasonable prior notice of entry into
      the Premises, which may be given orally to Tenant's facilities manager,
      will use reasonable efforts to schedule any such entry so as to cooperate
      with Tenant's schedule and to minimize any interruption to Tenant's
      business operations, and will allow Tenant to accompany Landlord during
      any such entry. Entry by Landlord shall not constitute constructive
      eviction or entitle Tenant to an abatement or reduction of Rent.

11.   ASSIGNMENT AND SUBLETTING.

      (a)   Generally. Except in connection with a Permitted Transfer (defined
            below), Tenant shall not assign, sublease, transfer or encumber any
            interest in this Lease or allow any third party to use any portion
            of the Premises (collectively or individually, a "Transfer") without
            the prior written consent of Landlord, which consent shall not be
            unreasonably withheld if Landlord does not elect to exercise its
            termination rights below. It is agreed that Landlord's consent shall
            not be considered unreasonably withheld if: (1) the proposed use is
            not the Permitted Use; (2) the proposed transferee's financial
            condition, in the event of an assignment, does not meet the criteria
            Landlord uses to select Building tenants having similar leasehold
            obligations; (3) the proposed transferee's business is not suitable
            for the Building considering the business of the other tenants, or
            would result in a violation of another tenant's rights; (4) the
            proposed transferee is a governmental agency or a present or
            prospective occupant of the Building; (5) Tenant is in default after
            the expiration of the notice and cure periods in this Lease; or (6)
            any portion of the Building or Premises would likely become subject
            to additional or different Laws as a consequence of the proposed
            Transfer. Notwithstanding the foregoing, so-called "co-location"
            (i.e., the leasing or licensing of a portion of the Premises on an
            equipment, equipment rack or services basis to additional parties in
            connection with the provision of Tenant's telecommunication services
            to or from Tenant's customers, vendors and other persons having a
            business relationship with Tenant (and such customers', vendors' or
            other persons' provision of

                                       17
<PAGE>   21
            telecommunication services to or from additional entities) in the
            normal course of Tenant's business (or the business of such
            additional entities) and not as a method for circumventing the other
            provisions of this Article 11 (as used herein, "Co-location")) will
            not be considered a Transfer hereunder. Tenant will indemnify,
            defend, protect and hold Landlord harmless from and against any and
            all loss, cost, damages or liability arising out of any damage to
            the Premises or Building associated with or caused by or because of
            such Co-location. Tenant shall not be entitled to receive monetary
            damages based upon a claim that Landlord unreasonably withheld its
            consent to a proposed Transfer and Tenant's sole remedy shall be an
            action to enforce any such provision through specific performance or
            declaratory judgment. Any attempted Transfer in violation of this
            Article shall, at Landlord's option, be void. Consent by Landlord to
            one or more Transfer(s) shall not operate as a waiver of Landlord's
            rights to approve any subsequent Transfers. In no event shall any
            Transfer or Permitted Transfer release or relieve Tenant from any
            obligation under this Lease.

      (b)   Request; Landlord's Options. As part of its request for Landlord's
            consent to a Transfer, Tenant shall provide Landlord with financial
            statements (audited if available) for the proposed transferee, a
            complete copy of the proposed assignment, sublease and other
            contractual documents and such other information as Landlord may
            reasonably request. Landlord shall, by written notice to Tenant
            within thirty (30) days of its receipt of the required information
            and documentation, either: (1) consent to the Transfer by the
            execution of a consent agreement in a form reasonably designated by
            Landlord or reasonably refuse to consent to the Transfer in writing;
            or (2) except in the case of a Permitted Transfer or a proposed
            Transfer to an entity controlled by or under common control with
            Tenant, exercise its right to terminate this Lease with respect to
            the portion of the Premises that Tenant is proposing to assign or
            sublet together with, at Landlord's option, a pro rata share of the
            Equipment Space and/or any parking spaces provided Tenant hereunder.
            Any such termination described in clause (2) above shall be
            effective on the proposed effective date of the Transfer for which
            Tenant requested consent. Tenant shall pay to Landlord, Landlord's
            actual costs (including reasonable attorney's fees) incurred in
            Landlord's review of any Permitted Transfer (defined below) or
            requested Transfer.

      (c)   Excess Consideration. Tenant shall pay Landlord fifty percent (50%)
            of all rent and other consideration which Tenant receives as a
            result of a Transfer that is in excess of the Rent payable to
            Landlord for the portion of the Premises and Term covered by the
            Transfer. Tenant shall pay Landlord for Landlord's share of any
            excess within thirty (30) days after Tenant's receipt of such excess
            consideration. If Tenant is in Monetary Default (defined below),
            Landlord may require that all sublease payments be made directly to
            Landlord, in which case Tenant shall receive a credit against Rent
            in the amount of any payments received (less Landlord's share of any
            excess). In determining excess rent in connection with an assignment
            or subletting, Tenant may, on an amortized basis, deduct the
            following expenditures resulting from such subletting or assignment:
            (1) commercially reasonable brokerage and marketing fees; and (2)
            reasonable legal fees and (3) the reasonable cost incurred by Tenant
            to construct demising walls to separate the area that is the subject
            of such Transfer from the remainder of the Premises and to
            reconfigure Tenant's systems (such as security systems) so as to
            serve the remainder of the Premises but not the portion that is the
            subject of such Transfer.

      (d)   Transfer of Shares/Rights: Permitted Transfers. Except as provided
            below with respect to a Permitted Transfer, if Tenant is a
            corporation, limited liability company, partnership, or similar
            entity, and controls ownership of a majority of the voting
            shares/rights at any time changes for any reason (including but not
            limited to a merger, consolidation or reorganization or purchase of
            substantially all of Tenant's assets), such change of ownership
            or control shall constitute a Transfer. The foregoing shall not
            apply so long as Tenant is an entity whose outstanding stock is
            listed on a recognized security exchange, or if at least fifty
            percent (50%) of its voting stock is owned by another entity, the
            voting stock of which is so listed. Notwithstanding the foregoing,
            Tenant may assign its entire interest under this Lease to a
            successor to Tenant by purchase, merger, consolidation or
            reorganization or to an entity that controls, is controlled by or is
            under common control with Tenant

                                       18
<PAGE>   22
            without the consent of Landlord, provided that all of the following
            conditions are satisfied (a "Permitted Transfer"): (1) Tenant is not
            in default (beyond the applicable notice and cure periods) under
            this Lease; (2) Tenant's successor (in the case of a purchase,
            merger, consolidation or reorganization) shall own all or
            substantially all of the assets of Tenant; (3) Tenant's successor
            shall have a net worth, as demonstrated to Landlord's reasonable
            satisfaction, which is at least equal to the greater of Tenant's net
            worth at the date of this Lease or Tenant's net worth as of the day
            prior to the proposed Transfer; (4) the Premises are to be used for
            the Permitted Use and for no other use whatsoever; (5) Tenant shall
            give Landlord written notice at least fifteen (15) days prior to the
            effective date of the proposed purchase, merger, consolidation or
            reorganization. Tenant's notice to Landlord shall include
            information and documentation establishing that each of the above
            conditions has been satisfied.

12.   LIENS.

      Tenant shall not permit mechanic's or other liens to be placed upon the
      Property, Premises or Tenant's leasehold interest in connection with any
      work or service done or purportedly done by or for benefit of Tenant. If a
      lien is so placed, Tenant shall, within twenty (20) days of notice from
      Landlord of the filing of the lien, fully discharge the lien by settling
      the claim which resulted in the lien or by bonding or insuring over the
      lien in the manner prescribed by the applicable lien Law. If Tenant fails
      to discharge the lien, then, in addition to any other right or remedy of
      Landlord, Landlord may bond or insure over the lien or otherwise discharge
      the lien. Tenant shall reimburse Landlord for any amount paid by Landlord
      to bond or insure over the lien or discharge the lien, including, without
      limitation, reasonable attorneys' fees within thirty (30) days after
      receipt of an invoice from Landlord. Notwithstanding the foregoing,
      Landlord acknowledges that all of Tenant's assets are pledged to Nortel
      Communications. Landlord agrees to execute and deliver the Landlord's
      Consent and Subordination attached hereto as Exhibit H.

13.   INDEMNITY AND WAIVER OF CLAIMS.

      (a)   Tenant's Indemnity. Except to the extent caused by the negligence
            or willful misconduct of Landlord or any Landlord Related Parties
            (defined below), Tenant shall indemnify, defend and hold Landlord,
            its trustees, members, principals, beneficiaries, partners,
            officers, directors, employees, Mortgagee(s) (defined in Article 26)
            and agents ("Landlord Related Parties") harmless against and from
            all liabilities, obligations, damages, penalties, claims, actions,
            costs, charges and expenses, including, without limitation,
            reasonable attorneys' fees and other professional fees, which may be
            imposed upon, incurred by or asserted against Landlord or any of the
            Landlord Related Parties and arising out of or in connection with
            any damage or injury occurring in the Premises, Equipment Space or
            Risers or any acts or omissions (including violations of Law) of
            Tenant, its trustees, members, principals, beneficiaries, partners,
            officers, directors, employees and agents ("Tenant Related Parties")
            or any of Tenant's transferees, contractors or licensees.

      (b)   Exculpation. Landlord and the Landlord Related Parties shall not be
            liable for, and Tenant waives, all claims for loss or damage to
            Tenant's business or loss, theft or damage to Leasehold Improvements
            or Tenant's Property or the property of any person claiming by,
            through or under Tenant resulting from: (1) wind or weather; (2) the
            failure of any sprinkler, heating or air-conditioning equipment, any
            electric wiring or any gas, water or steam pipes (except, with
            respect to this clause (2), to the extent of any property damage
            caused by the negligence of Landlord which is not covered by
            insurance required to be maintained by Tenant hereunder [Landlord
            will additionally be responsible for Tenant's deductible payment in
            such case]); (3) the backing up of any sewer pipe or downspout; (4)
            the bursting, leaking or running of any tank, water closet, drain or
            other pipe; (5) water, snow or ice upon or coming through the roof,
            skylight, stairs, doorways, windows, walks or any other place upon
            or near the Building; (6) any act or omission of any party other
            than Landlord or Landlord Related Parties; and (7) any causes not
            reasonably within the control of Landlord, Tenant shall insure
            itself against such losses under Article 14 below.

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<PAGE>   23
      (c)   Landlord's Indemnity. Except to the extent such losses, liabilities,
            obligations, damages, penalties, claims, costs, charges and expenses
            result from the negligence of Tenant or any Tenant Related Parties,
            Landlord shall indemnify and hold Tenant harmless from and against
            all liabilities, obligations, damages (other than consequential
            damages), penalties, claims, costs, charges and expenses, including,
            without limitation, reasonable attorneys' fees, which may be imposed
            upon, incurred by, or asserted against Tenant by any third parties
            and arising, directly or indirectly, out of or in connection with
            any injury or damage to any person or property occurring in, on or
            about the Common Areas or any part thereof; provided, however, that
            in each case such liability, obligation, damage, penalty, claim,
            cost, charge or expense results from the negligence or willful
            misconduct of Landlord and/or its agents, employees or contractors.

14.   INSURANCE.

      Tenant shall carry and maintain the following insurance ("Tenant's
      Insurance"), at its sole cost and expense: (1) Commercial General
      Liability Insurance applicable to the Premises, the Equipment Space, the
      portion of any Risers containing Tenant's Cable and their respective
      appurtenances providing, on an occurrence basis, a minimum combined single
      limit of $5,000,000.00; (2) All Risk Property/Business Interruption
      Insurance, written at replacement cost value and with a replacement cost
      endorsement covering all of Tenant's trade fixtures, equipment, furniture
      and other personal property within or serving the Premises, any Leasehold
      Improvements, and Site Equipment as well as all Cable ("Tenant's
      Property"); (3) Workers' Compensation Insurance as required by the state
      in which the Premises is located and in amounts as may be required by
      applicable statute; and (4) Employers Liability Coverage of at least
      $1,000,000.00 per occurrence; and (5) such other amounts, types or levels
      of insurance as Landlord may reasonably prescribe, including, without
      limitation, increases in the levels of coverage described above. Any
      company writing any of Tenant's Insurance shall have an A.M. Best rating
      of not less than A-VIII. All Commercial General Liability Insurance
      policies shall name Tenant as a named insured and Landlord (or any
      successor), any property manager retained by Landlord to manage the
      Building, and their respective members, principals, beneficiaries,
      partners, officers, directors, employees, and agents, and other designees
      of Landlord as the interest of such designees shall appear, as additional
      insureds. All policies of Tenant's Insurance shall contain endorsements
      that the insurer(s) shall give Landlord and its designees at least thirty
      (30) days' advance written notice of any change, cancellation, termination
      or lapse of insurance. Tenant shall provide Landlord with a certificate of
      insurance evidencing Tenant's Insurance prior to the earlier to occur of
      the Commencement Date or the date Tenant is provided with possession of
      the Premises for any reason, and upon renewals at least five (5) days
      prior to the expiration of the insurance coverage. Provided Tenant
      delivers to Landlord audited financial statements, reasonably
      satisfactory to Landlord evidencing that Tenant has a net worth as
      measured by its retained earnings ("Net Worth") in the amount of
      $25,000,000.00 or more as of the date of said statement, Tenant may
      self-insure for the All Risk Property Insurance coverage specified in this
      Section with respect to Tenant's trade fixtures and computer and/or
      telecommunications equipment located within the Premises. If Landlord
      permits Tenant to self-insure in accordance with the foregoing, then in
      order to be permitted to maintain such self-insurance, Tenant must
      maintain throughout the Lease Term a Net Worth of at least $25,000,000.00,
      and deliver to Landlord, within ninety (90) days after the end of each of
      Tenant's fiscal years, a statement in the form described above evidencing
      Tenant's Net Worth. If at any time Tenant's Net Worth is less than the
      amount set forth above, then Tenant must obtain, provide, and keep in full
      force and effect the above referenced insurance coverage with respect to
      Tenant's trade fixtures and computer and/or telecommunications equipment
      located within the Premises and provide Landlord with evidence of the
      same. Landlord shall maintain so called All Risk property insurance on the
      Building at replacement cost value, as reasonably estimated by Landlord,
      as well as Commercial General Liability insurance coverage in an amount
      not less than $5,000,000 with respect to the Property. Landlord's
      insurance coverage shall be sufficient so as to not trigger any
      co-insurance requirements with respect to any applicable insurer. Except
      as specifically provided to the contrary, the limits of either party's
      insurance shall not limit such party's liability under this Lease.

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<PAGE>   24
15.   SUBROGATION.

      Notwithstanding anything in this Lease to the contrary, Landlord and
      Tenant each waive, and shall cause their respective insurance carriers to
      waive, any and all rights of recovery, claim, action or causes of action
      against the other and their respective trustees, principals,
      beneficiaries, partners, officers, directors, agents, and employees, for
      any loss or damage that may occur to Landlord or Tenant or any party
      claiming by, through or under Landlord or Tenant, as the case may be, with
      respect to Tenant's Property, the Building, the Premises and the Equipment
      Space, any additions or improvements to the foregoing, or any contents
      thereof, including all rights of recovery, claims, actions or causes of
      action arising out of the negligence of Landlord or any Landlord Related
      Parties or the negligence of Tenant or any Tenant Related Parties, which
      loss or damage is (or would have been, had the insurance required by this
      Lease been carried) covered by insurance.

16.   CASUALTY DAMAGE.

      (a)   Landlord's Options. If all or any part of the Premises is damaged by
            fire or other casualty, Tenant shall immediately notify Landlord in
            writing. During any period of time that Tenant is unable to conduct
            its business from the Premises, as a result of a fire or other
            casualty, the Rent shall abate for the portion of the Premises that
            is not usable, and not used, by Tenant. Landlord shall have the
            right to terminate this Lease if: (1) the Building shall be damaged
            so that, in Landlord's reasonable judgment, substantial alteration
            or reconstruction of the Building (i.e., work which will take in
            excess of one hundred eighty (180) days) shall be required (whether
            or not the Premises has been damaged); (2) Landlord is not permitted
            by Law to rebuild the Building in substantially the same form as
            existed before the fire or casualty; (3) the Premises have been
            materially damaged and there is less than two (2) years of the Term
            remaining on the date of the casualty; (4) any Mortgagee requires
            that the insurance proceeds be applied to the payment of the
            mortgage debt; or (5) a material uninsured loss (not required to be
            insured against by Landlord hereunder) to the Building occurs.
            Landlord may exercise its right to terminate this Lease by notifying
            Tenant in writing within one hundred twenty (120) days after the
            date of the casualty. If Landlord does not terminate this Lease,
            Landlord shall commence and proceed with reasonable diligence to
            repair and restore the Building (excluding any Tenant's Property,
            which Tenant shall repair). In no event shall Landlord be required
            to spend more than the insurance proceeds received by Landlord.
            Landlord shall not be liable for any loss or damage to Tenant's
            Property or to the business of Tenant resulting in any way from the
            fire or other casualty or from the repair and restoration of the
            damage. Landlord and Tenant hereby waive the provisions of any Law
            relating to the matters addressed in this Article, and agree that
            their respective rights for damage to or destruction of the Premises
            shall be those specifically provided in this Lease.

      (b)   Tenant's Option. If all or any portion of the Premises shall be made
            untenantable by fire or other casualty, Landlord shall, with
            reasonable promptness, cause an architect or general contractor
            selected by Landlord to provide Landlord and Tenant with a written
            estimate of the amount of time required to substantially complete
            the repair and restoration of the Premises and make the Premises
            tenantable again, using standard working methods ("Completion
            Estimate"). Landlord will use diligent efforts to provide the
            Completion Estimate within sixty (60) days following the date of the
            damage. If the Completion Estimate indicates that the Premises
            cannot be made tenantable within two hundred ten (210) days from the
            date the repair and restoration is started, then regardless of
            anything in Section 16(a) above to the contrary, either party shall
            have the right to terminate this Lease by giving written notice to
            the other of such election within ten (10) days after receipt of the
            Completion Estimate. Notwithstanding the foregoing, if Tenant was
            entitled to but elected not to exercise its right to terminate this
            Lease and Landlord does not substantially complete the repair and
            restoration the Premises within two (2) months after the expiration
            of the estimated period of time set forth in the Completion
            Estimate, which period shall be extended to the extent of any
            Reconstruction Delays, then Tenant may terminate this Lease by
            written notice to Landlord within fifteen (15) days after the
            expiration of such period, as the same may be extended. For purposes
            of

                                       21
<PAGE>   25
            this Section 16(b), the term "Reconstruction Delays" shall mean: (i)
            any delays caused by the insurance adjustment process; (ii) any
            delays caused by Tenant; and (iii) any delays caused by events of
            Force Majeure. If Tenant elects to terminate this Lease, the
            effective date of such termination shall be specified in Tenant's
            notice to Landlord, but may be at least sixty (60) days following
            Tenant's notice to Landlord in order to allow Tenant sufficient time
            to dismantle and remove Tenant Property (and any Co-location
            property); provided, however, that Landlord shall have the right to
            be exercised by written notice delivered to Tenant within ten (10)
            business days following receipt of any termination notice from
            Tenant to cause the effective date of such termination to be
            accelerated from the date specified in Tenant's notice, if such
            acceleration is made necessary due to safety reasons, construction
            schedules, or other causes beyond Landlord's reasonable control.

17.   CONDEMNATION.

      Either party may terminate this Lease if the whole or any material part of
      the Premises shall be taken or condemned for any public or quasi-public
      use under Law, by eminent domain or private purchase in lieu thereof (a
      "Taking"). Landlord shall also have the right to terminate this Lease if
      there is a Taking of any portion of the Building or Property which would
      leave the remainder of the Building unsuitable for use in a manner
      comparable to the Building's use prior to the Taking. Tenant shall also
      have the right to terminate this Lease if a permanent Taking of any
      portion of the Building renders all or any part of the Premises or
      Equipment Space untenantable such that Tenant may not use the Premises for
      the conduct of Tenant's business operations. In order to exercise its
      right to terminate the Lease, Landlord or Tenant, as the case may be, must
      provide written notice of termination to the other within forty-five (45)
      days after the terminating party first receives notice of the Taking. Any
      such termination shall be effective as of the date the physical taking of
      the Premises or the portion of the Building or Property occurs; provided,
      however, that if such Taking is not a Taking of the Premises and/or
      Equipment Space, Tenant may, subject to the approval of the condemning
      authority and Landlord, request that the effective date of such
      termination be at least sixty (60) days following the notice of
      termination, in order to allow Tenant sufficient time to effect an orderly
      dismantling and removal of Tenant's Property (and any Co-location
      property). If this Lease is not terminated, the Rentable Square Footage of
      the Building, the Rentable Square Footage of the Premises and Tenant's Pro
      Rata Share shall, if applicable, be appropriately adjusted. In addition,
      Rent for any portion of the Premises taken or condemned shall be abated
      during the unexpired Term of this Lease effective when the physical taking
      of the portion of the Premises occurs. All compensation awarded for a
      Taking, or sale proceeds, shall be the property of Landlord, any right to
      receive compensation or proceeds being expressly waived by Tenant.
      However, Tenant may file a separate claim at its sole cost and expense for
      Tenant's Property and Tenant's reasonable relocation expenses, provided
      the filing of the claim does not diminish the award which would otherwise
      be receivable by Landlord.

18.   SECURITY DEPOSIT.

      Tenant shall deliver Tenant's Security Deposit to Landlord, together with
      the first (1st) month's payment of Base Rent and Equipment Space Rent,
      concurrently with Tenant's delivery to Landlord of this Lease as executed
      by Tenant, shall be held by Landlord, without liability for interest, as
      security for the performance of Tenant's obligations under this Lease.
      Landlord shall not be required to keep the Security Deposit segregated
      from other funds of Landlord. Tenant shall not assign or in any way
      encumber the Security Deposit. Upon the occurrence of any default by
      Tenant, Landlord shall have the right, without prejudice to any other
      remedy, to use the Security Deposit, or portions thereof, to the extent
      necessary to pay any arrearages in Rent, and any other damage, injury or
      expense. Following any such application of all or any portion of the
      Security Deposit, Tenant shall pay to Landlord, within thirty (30) days
      following demand, the amount so applied in order to restore the Security
      Deposit to its original amount. Provided Tenant is not in default
      hereunder, Landlord will return any unapplied portion of the Security
      Deposit to Tenant within thirty (30) days following the later to occur of
      (i) the expiration of the Term, (ii) the final reconciliation and payment
      of Operating Expenses and Property Taxes payable hereunder by Tenant and
      (iii) Tenant's vacancy of the Premises and Building in accordance with the
      provisions of this Lease.

                                       22
<PAGE>   26
19.   EVENTS OF DEFAULT.

      Tenant shall be considered to be in default of this Lease upon the
      occurrence of any of the following events of default:

      (a)   Monetary Default. Tenant's failure to pay when due all or any
            portion of the Rent ("Monetary Default") within ten (10) days after
            written notice to Tenant; provided, that Landlord shall be required
            to deliver any such notice only twice during any twelve (12) month
            period, and any subsequent failure to pay any Rent when due in any
            twelve (12) month period following Landlord's delivery of written
            notice of Monetary Default shall automatically be a default, without
            the necessity of written notice from Landlord or a ten (10) day
            grace period.

      (b)   Non-Monetary Default. Tenant's failure (other than a Monetary
            Default) to comply with any term, provision or covenant of this
            Lease, if the failure is not cured within twenty (20) days after
            written notice to Tenant. However, if Tenant's failure to comply
            cannot reasonably be cured within twenty (20) days, Tenant shall be
            allowed additional time (not to exceed sixty (60) days) as is
            reasonably necessary to cure the failure so long as: (1) Tenant
            commences to cure the failure within twenty (20) days, and (2)
            Tenant diligently pursues a course of action that will cure the
            failure and bring Tenant back into compliance with the Lease.
            However, if Tenant's failure to comply creates a hazardous
            condition, the failure must be cured immediately upon notice to
            Tenant. In addition, if Tenant fails to timely comply with this
            Section 19(b) with respect to any particular term, provision or
            covenant of the Lease on two (2) occasions during any twelve (12)
            month period, Tenant's subsequent violation of such term, provision
            or covenant shall, at Landlord's option, be an incurable event of
            default by Tenant.

      (c)   Insolvency Matters. Tenant becomes insolvent, makes a transfer in
            fraud of creditors, or files a petition in bankruptcy, or makes an
            assignment for the benefit of creditors, or admits in writing its
            inability to pay its debts when due.

      (d)   Taking of Leasehold Estate. The leasehold estate is taken by process
            or operation of Law.

      (e)   Landlord Default.

            (i)   Landlord shall not be in default hereunder unless Landlord
                  tails to comply with any obligation of Landlord pursuant to
                  the provisions of this Lease, and such failure is not cured
                  within twenty (20) days after written notice to Landlord from
                  Tenant, or such additional time as is reasonably necessary to
                  cure such failure so long as (i) Landlord commences the cure
                  of such failure within twenty (20) days following the giving
                  of Tenant's. notice, and (ii) Landlord diligently pursues a
                  course of action that will cure the failure and bring Landlord
                  back into compliance with this Lease. Any notice of default
                  provided by Tenant to Landlord shall be concurrently delivered
                  to Landlord's Mortgagee (provided Tenant has notice of the
                  existence of any such Mortgagee) and any such Mortgagee shall
                  have an equivalent opportunity to cure any default on the part
                  of Landlord hereunder prior to Tenant exercising its right as
                  set forth herein specifying in reasonable detail the nature of
                  the failure in question.

            (ii)  In the event of a default by Landlord hereunder as described
                  above, Tenant shall have the right to pursue its remedies
                  under applicable law, which may include, if applicable,
                  equitable remedies such as the remedy of specific performance.
                  Tenant's remedies shall be cumulative and not exclusive.

                                       23
<PAGE>   27
20.   REMEDIES.

      (a)   Generally. Upon any default, Landlord shall have the right without
            notice or demand (except as provided in Article 19) to pursue any of
            its rights and remedies at Law or in equity, including any one or
            more of the following remedies:

            (i)   Terminate this Lease, in which case Tenant shall immediately
                  surrender the Premises and Equipment Space to Landlord. If
                  Tenant fails to surrender the Premises and/or Equipment Space,
                  Landlord may, in compliance with applicable Law and without
                  prejudice to any other right or remedy, enter upon and take
                  possession of the Premises and/or Equipment Space and expel
                  and remove Tenant, Tenant's Property and any party occupying
                  all or any part of the Premises and/or Equipment Space. Tenant
                  shall pay Landlord on demand the amount of all past due Rent
                  and other losses and damages which Landlord may suffer as a
                  result of Tenant's default, whether by Landlord's inability to
                  relet the Premises and/or Equipment Space on satisfactory
                  terms or otherwise, including, without limitation, all Costs
                  of Reletting (defined below) and any deficiency that may arise
                  from reletting or the failure to relet the Premises and/or
                  Equipment Space. "Costs of Reletting" shall include all
                  reasonable costs and expenses incurred by Landlord in
                  reletting or attempting to relet the Premises and/or Equipment
                  Space, including, without limitation, reasonable legal fees,
                  brokerage commissions, the cost of alterations and the value
                  of other concessions or allowances granted to a new tenant.

            (ii)  Terminate Tenant's right to possession of the Premises and/or
                  Equipment Space and, in compliance with applicable Law, expel
                  and remove Tenant, Tenant's Property and any parties occupying
                  all or any part of the Premises and/or Equipment Space.
                  Landlord may (but shall not be obligated to) relet all or any
                  part of the Premises and/or Equipment Space, without notice to
                  Tenant, for a term that may be greater or less than the
                  balance of the Term and on such conditions (which may include
                  concessions, free rent and alterations of the Premises and/or
                  Equipment Space) and for such uses as Landlord in its absolute
                  discretion shall determine. Landlord may collect and receive
                  all rents and other income from the reletting. Tenant shall
                  pay Landlord on demand all past due Rent, all Costs of
                  Reletting and any deficiency arising from the reletting or.
                  failure to relet the Premises and/or Equipment Space. Landlord
                  shall not be responsible or liable for the failure to relet
                  all or any part of the Premises and/or Equipment Space or for
                  the failure to collect any Rent. The re-entry or taking of
                  possession of the Premises and/or Equipment Space shall not be
                  construed as an election by Landlord to terminate this Lease
                  unless a written notice of termination is given to Tenant.

            (iii) In lieu of calculating damages under Sections 20(a)(i) or
                  20(a)(ii) above, Landlord may elect to receive as damages the
                  sum of (a) all Rent accrued through the date of termination of
                  this Lease or Tenant's right to possession, and (b) an amount
                  equal to the total Rent that Tenant would have been required
                  to pay for the remainder of the Term discounted to present
                  value at the Prime Rate (defined in Section 20(b) below) then
                  in effect, minus the then present fair rental value of the
                  Premises for the remainder of the Term, similarly discounted,
                  after deducting all anticipated Costs of Reletting.

      (b)   Remedies; Cumulative Interest. Unless expressly provided in this
            Lease, the repossession or reentering of all or any part of the
            Premises and/or Equipment Space shall not relieve Tenant of its
            liabilities and obligations under the Lease. No right or remedy of
            Landlord shall be exclusive of any other right or remedy. Each right
            and remedy shall be cumulative and in addition to any other right
            and remedy now or subsequently available to Landlord at Law or in
            equity. If Landlord declares Tenant to be in default, Landlord shall
            be entitled to receive interest on any unpaid item of Rent at an
            annual rate equal to the Prime Rate plus four percent (4%). For
            purposes hereof, the "Prime Rate" shall be the per annum interest
            rate publicly announced as its prime or base rate by a federally

                                       24
<PAGE>   28
            insured bank selected by Landlord in the state in which the Building
            is located. Forbearance by Landlord to enforce one or more remedies
            shall not constitute a waiver of any default.

21.   LIMITATION OF LIABILITY; LANDLORD'S TRANSFER.

      Notwithstanding anything to the contrary contained in this Lease, the
      liability of Landlord (and of any successor Landlord) to Tenant shall be
      limited to the equity interest of Landlord in the Building, including all
      rents, proceeds and profits therefrom. Tenant shall look solely to
      Landlord's equity interest in the Building for the recovery of any
      judgment or award against Landlord. Neither Landlord nor any Landlord
      Related Party shall be personally liable for any judgment or deficiency.
      Before filing suit for an alleged default by Landlord, Tenant shall give
      Landlord and the Mortgagee(s) (defined in Article 26 below) whom Tenant
      has been notified hold Mortgages (defined in Article 26 below) on the
      Property, Building, Premises or Equipment Space, notice and reasonable
      time to cure the alleged default. Landlord shall have the right to
      transfer and assign, in whole or in part, all of its rights and
      obligations under this Lease and in the Building and/or Property referred
      to herein, and upon such transfer Landlord shall be released from any
      further obligations hereunder, and Tenant agrees to look solely to the
      successor in interest of Landlord for the performance of such obligations.

22.   NO WAIVER.

      Either party's failure to declare a default immediately upon its
      occurrence, or delay in taking action for a default shall not constitute a
      waiver of the default. Either party's failure to enforce its rights for a
      default shall not constitute a waiver of its rights regarding any
      subsequent default. Receipt by Landlord of Tenant's keys to the Premises
      shall not constitute an acceptance or surrender of the Premises.

23.   QUIET ENJOYMENT.

      Tenant shall, and may peacefully have, hold and enjoy the Premises and
      Equipment Space, subject to the terms of this Lease, provided Tenant pays
      the Rent and fully performs all of its covenants and agreements. This
      covenant and all other covenants of Landlord shall be binding upon
      Landlord and its successors only during its or their respective periods of
      ownership of the Building, and shall not be a personal covenant of
      Landlord or the Landlord Related Parties.

24.   RELOCATION.

      [INTENTIONALLY OMITTED]

25.   HOLDING OVER.

      If Tenant falls to surrender the Premises and Equipment Space at the
      expiration or earlier termination of this Lease, occupancy of the Premises
      and/or Equipment Space after the termination or expiration shall be that
      of a tenancy at sufferance. Tenant's occupancy of the Premises and/or
      Equipment Space during the holdover shall be subject to all the terms and
      provisions of this Lease and Tenant shall pay an amount (on a per month
      basis without reduction for partial months during the holdover) equal to
      one hundred fifty percent (150%) of the Rent due for the period
      immediately preceding the holdover. No holdover by Tenant or payment by
      Tenant after the expiration or early termination of this Lease shall be
      construed to extend the Term or prevent Landlord from immediate recovery
      of possession of the Premises and/or Equipment Space by summary
      proceedings or otherwise. In addition to the payment of the amounts
      provided above, Tenant shall be liable to Landlord for all damages,
      including, without limitation, consequential damages, that Landlord
      suffers from the holdover. Notwithstanding the foregoing, Tenant shall not
      be liable for consequential damages unless: (1) Landlord notifies Tenant
      that it has entered into a lease for all or a portion of the Premises or
      has received a bona fide offer to lease all or a portion of the Premises;
      and (2) Tenant fails to vacate the Premises within fifteen (15) days after
      the later to occur of (x) the Expiration Date and (y) the date of
      Landlord's notice.

                                       25
<PAGE>   29
26.   SUBORDINATION TO MORTGAGES; ESTOPPEL CERTIFICATE.

      Tenant accepts this Lease subject and subordinate to any mortgage(s),
      deed(s) of trust, ground lease(s) or other lien(s) now or subsequently
      arising upon the Building or the Property, and to renewals, modifications,
      refinancings and extensions thereof (collectively referred to as a
      "Mortgage"). The party having the benefit of a Mortgage shall be referred
      to as a "Mortgagee". This clause shall be self-operative, but upon request
      from a Mortgagee, Tenant shall execute a commercially reasonable
      subordination agreement in favor of the Mortgagee. In lieu of having the
      Mortgage be superior to this Lease, a Mortgagee shall have the right at
      any time to subordinate its Mortgage to this Lease. If reasonably
      requested by a successor-in-interest to all or a part of Landlord's
      interest in the Lease, Tenant shall, without charge, attorn to the
      successor-in-interest. Landlord and Tenant shall each, within twenty (20)
      days after receipt of a written request from the other, execute and
      deliver an estoppel certificate to those parties as are reasonably
      requested by the other (including a Mortgagee or prospective purchaser).
      The estoppel certificate shall include a statement certifying that this
      Lease is unmodified (except as identified in the estoppel certificate) and
      in full force and effect, describing the dates to which Rent and other
      charges have been paid, representing that, to such party's actual
      knowledge, there is no default (or stating the nature of the alleged
      default) and indicating other matters with respect to the Lease that may
      reasonably be requested. Tenant agrees to modify this Lease as reasonably
      requested by any Mortgagee, provided such modifications do not materially
      impair Tenant's rights or increase Tenant's obligations under the Lease.
      Landlord will use reasonable efforts to obtain a non-disturbance,
      subordination and attornment agreement from Landlord's then
      current-Mortgagee on such Mortgagee's then current standard form of
      agreement, by which form such Mortgagee shall agree to recognize Tenant as
      a tenant in accordance with the terms of this Lease. "Reasonable efforts"
      of Landlord shall not require Landlord to incur any cost, expense or
      liability to obtain such agreement, it being agreed that Tenant shall be
      responsible for any fee or review costs charged by Mortgagee. Upon request
      of Landlord, Tenant will execute the Mortgagee's form of non-disturbance,
      subordination and attornment agreement (subject to Tenant's approval,
      which will not be unreasonably withheld, conditioned or delayed) and
      return the same to Landlord for execution by the Mortgagee. Landlord's
      failure to obtain a non-disturbance, subordination and attornment
      agreement for Tenant shall have no effect on the rights, obligations and
      liabilities of Landlord and Tenant or be considered to be a default by
      Landlord hereunder.

27.   ATTORNEYS' FEES.

      If either party institutes a suit against the other for violation of or to
      enforce any covenant or condition of this Lease, or it either party
      intervenes in any suit in which the other is a party to enforce or protect
      its interest or rights, the prevailing party shall be entitled to all of
      its costs and expenses, including, without limitation, reasonable
      attorneys' fees.

28.   NOTICES.

      If a demand, request, approval, consent or notice (collectively referred
      to as a "Notice") shall or may be given to either party by the other, the
      Notice shall be in writing and delivered by hand or sent by registered or
      certified mail with return receipt requested, or sent by overnight or same
      day courier service at the party's respective Notice Address(es) set forth
      in Article 1, except that if Tenant has vacated the Premises (or if the
      Notice Address for Tenant is other than the Premises, and Tenant has
      vacated such address) without providing Landlord a new Notice Address,
      Landlord may serve Notice in any manner described in this Article or in
      any other manner permitted by Law. Notice shall be deemed to have been
      received or given on the earlier to occur of (i) actual delivery, or the
      date on which delivery is refused, or (ii) if Tenant has vacated the
      Premises or the other Notice Address of Tenant without providing a new
      Notice Address, three (3) days after Notice is deposited in the U.S. mail
      or with a courier service in the manner described above. Either party may,
      at any time, change its Notice Address by giving the other party written
      Notice of the new address in the manner described in this Article.

                                       26
<PAGE>   30
29.   EXCEPTED RIGHTS.

      This Lease does not grant any rights to light or air over or about the
      Building. Except as expressly set forth in this Lease, Landlord excepts
      and reserves exclusive to itself the use of: (1) roofs, (2) telephone,
      electrical and janitorial closets, (3) equipment rooms, (4) rights to the
      land and improvements below the floor of the Premises, (5) the
      improvements and air rights above the Premises, (6) the improvements and
      air rights outside the demising walls of the Premises, and (7) the areas
      within the Premises used for the installation of utility lines and other
      installations serving all occupants of the Building (Tenant acknowledges
      that Landlord or Building tenants may run conduits through the Premises in
      order to serve the Building's operation of the Meet-Me Room and thereafter
      enter the Premises to maintain such conduit; the approved location and
      dimensions of such conduit are attached as part of Exhibit A). Landlord
      has the right to change the Building's name or (if required by
      governmental authority) address. Landlord also has the right to make such
      other changes to the Property and Building as Landlord deems appropriate
      (including the right to add additional floors to the Building or to reduce
      the size of the Building), provided the changes do not materially affect
      Tenant's ability to use, occupy or conduct Tenant's business from the
      Premises or the Equipment Space and do not increase any amount payable by
      Tenant. hereunder. Landlord shall also have the right (but not the
      obligation) to temporarily close the Building if Landlord reasonably
      determines that there is an imminent danger of significant damage to the
      Building or of personal injury to Landlord's employees or the occupants of
      the Building. The circumstances under which Landlord may temporarily close
      the Building shall include, without limitation, electrical interruptions,
      hurricanes and civil disturbances. A closure of the Building under such
      circumstances shall not constitute a constructive eviction nor entitle
      Tenant to an abatement or reduction of Rent. Landlord reserves the right
      to temporarily reduce Tenant's allocation of parking spaces as required
      during modifications to the Property.

30.   SURRENDER OF PREMISES.

      At the expiration or earlier termination of this Lease or Tenant's right
      of possession, Tenant shall remove Tenant's Property from the Premises,
      Equipment Space and Risers (except that Tenant may leave behind any
      conduit provided all contents of the same are removed by Tenant), and quit
      and surrender the Premises, Equipment Space and the Risers (using
      Landlord's specified contractor to perform any such work affecting the
      Risers) to Landlord, broom clean, and in good order, condition and repair
      and in compliance with all applicable laws, ordinary wear and tear,
      casualty, condemnation and Landlord's maintenance obligations excepted;
      any such work will be performed in accordance with Article 8 above. If
      Tenant fails to so remove any of Tenant's Property prior to the
      termination of this Lease or of Tenant's right to possession, Landlord, at
      Tenant's sole cost and expense, shall be entitled (but not obligated) to
      remove and store Tenant's Property, Tenant shall pay Landlord, upon
      demand, the expenses and storage charges incurred for Tenant's Property.
      Landlord shall not be responsible for the value, preservation or
      safekeeping of Tenant's Property. In addition, if Tenant fails to remove
      Tenant's Property from the Premises or storage, as the case may be, within
      thirty (30) days after written Notice, Landlord may deem all or any part
      of Tenant's Property to be abandoned, and title to Tenant's Property shall
      be deemed to be immediately vested in Landlord.

31.   PARKING.

      Tenant shall be allowed in common with all other Building occupants to use
      the parking area associated with the Building for Tenant's parking
      requirements such parking spaces as Landlord, in Landlord's discretion
      from time-to-time, determines are available for such use. Tenant shall pay
      Landlord as Additional Rent hereunder the monthly parking rates as
      established by Landlord. Tenant shall not exceed its allocation of parking
      spaces as described herein. Tenant further agrees that Landlord shall not
      be responsible for enforcing Tenants rights to such use of the parking
      spaces.

32.   ENVIRONMENTAL MATTERS/HAZARDOUS MATERIALS.

      (a)   Hazardous Materials Disclosure Certificate. Prior to executing
            this Lease, Tenant has completed, executed and delivered to Landlord
            Tenants initial Hazardous Materials Disclosure Certificate (the

                                       27
<PAGE>   31
            "Initial HazMat Certificate"), a copy of which is attached hereto as
            EXHIBIT F and incorporated herein by this reference. Tenant
            covenants, represents and warrants to Landlord that, to the best of
            Tenant's knowledge after due inquiry, the information on the Initial
            HazMat Certificate is true and correct and accurately describes the
            use(s) of Hazardous Materials which will be made and/or used on the
            Premises or the Equipment Space by Tenant. Commencing with the date
            which is one year from the Commencement Date, and continuing every
            year thereafter, on thirty (30) days written notice from Landlord,
            Tenant will complete, execute, and deliver to Landlord, a Hazardous
            Materials Disclosure Certificate (the "HazMat Certificate")
            describing Tenant's present use of Hazardous Materials on the
            Premises or the Equipment Space, and any other reasonably necessary
            documents as requested by Landlord. The HazMat Certificate required
            hereunder shall be in substantially the form as that which is
            attached hereto as EXHIBIT F.

      (b)   Definition of Hazardous Materials. As used in this Lease, the term
            "Hazardous Materials" shall mean and include (i) any hazardous or
            toxic wastes, materials or substances, and other pollutants or
            contaminants, which are or become regulated by any Environmental
            Laws; (ii) petroleum, petroleum by products, gasoline, diesel fuel,
            crude oil or any fraction thereof; (iii) asbestos and asbestos
            containing material, in any form, whether friable or non-friable;
            (iv) polychlorinated biphenyls; (v) radioactive materials; (vi) lead
            and lead-containing materials; (vii) any other material, waste or
            substance displaying toxic, reactive, ignitable or corrosive
            characteristics, as all such terms are used in their broadest sense,
            and are defined or become defined by any Environmental Law (defined
            below); or (h) any materials which cause or threatens to cause a
            nuisance upon or waste to any portion of the Premises, Equipment
            Space, the Building, the Property or any surrounding property; or
            poses or threatens to pose a hazard to the health and safety of
            persons on the Premises, Equipment Space, Building, the Property or
            any surrounding property.

      (c)   Prohibition; Environmental Laws. Except for, and to the extent of,
            the Hazardous Materials specified in the Initial HazMat Certificate,
            Tenant shall not be entitled to use nor store any Hazardous
            Materials on, in, or about the Premises, Equipment Space, the
            Building, the Property, or any portion of the foregoing, without, in
            each instance, obtaining Landlord's prior written consent thereto,
            which consent shall not be unreasonably withheld, delayed or
            conditioned. If Landlord consents to any such usage or storage, then
            Tenant shall be permitted to use and/or store only those Hazardous
            Materials that are necessary for Tenant's business and to the extent
            disclosed in the HazMat Certificate and as expressly approved by
            Landlord in writing, provided that such usage and storage is only
            to the extent of the quantities of Hazardous Materials as specified
            in the then applicable HazMat Certificate as expressly approved by
            Landlord and provided further that such usage and storage is in full
            compliance with any and all local, state and federal environmental,
            health and/or safety-related laws, statutes, orders, standards,
            courts' decisions, ordinances, rules and regulations (as interpreted
            by judicial and administrative decisions), decrees, directives,
            guidelines, permits or permit conditions, currently existing and as
            amended, enacted, issued or adopted in the future which are or
            become applicable to Tenant or all or any portion of the Premises
            (collectively, the "Environmental Laws"). Tenant agrees that any
            changes to the type and/or quantities of Hazardous Materials
            specified in the most recent HazMat Certificate may be implemented
            only with the prior written consent of Landlord, which consent shall
            not be unreasonably withheld, delayed or conditioned. Landlord shall
            have the right at all reasonable times during the Term, upon
            reasonable advance notice to Tenant (except in the case of
            emergency) to (i) inspect the Premises and Equipment Space, (ii)
            conduct tests and investigations to determine whether Tenant is in
            compliance with the provisions of this Article 32, and (iii) request
            lists of all Hazardous Materials used, stored or otherwise located
            on, under or about the Building, Premises, Equipment Space, and the
            Property. The cost of all such inspections, tests and investigations
            shall be proportionately borne by Tenant commensurate with the
            extent of Hazardous Materials revealed by any such inspection, test
            or investigation to be present in, on or about the Premises,
            Equipment Space, Building or Property arising from or related to the
            intentional or negligent acts or omissions of Tenant or any of
            Tenant's employees, agents, contractors or representatives and all
            other costs and expenses shall be borne by parties other than
            Tenant. However, in the event any such inspection, test or

                                       28
<PAGE>   32
            investigation reveals that there are not any Hazardous Materials
            present in, on or about the Premises, Building, Equipment Space or
            Property arising from or related to the intentional or negligent
            acts or omissions of Tenant or Tenant's employees, agents,
            contractors or representatives then Tenant shall not be responsible
            for any of the cost of such inspections, tests and investigations.
            The aforementioned rights granted herein to Landlord and its
            representatives shall not create (a) a duty on Landlord's part to
            inspect, test, investigate, monitor or otherwise observe the
            Premises, Building, Equipment Space, Property or the activities of
            Tenant and Tenant's employees, agents, contractors or
            representatives or invitees with respect to Hazardous Materials,
            including without limitation, Tenant's operation, use and any
            remediation related thereto, or (b) liability on the part of
            Landlord and its representatives for Tenant's use, storage, disposal
            or remediation of Hazardous Materials, it being understood that
            Tenant shall be solely responsible for all liability in connection
            therewith.

      (d)   Tenant's Environmental Obligations. Tenant shall give to Landlord
            immediate verbal and follow-up written Notice of any spills,
            releases, discharges, disposals, emissions, migrations, removals or
            transportation of Hazardous Materials on, under or about the
            Premises, Equipment Space, Building or Property. Tenant, at its sole
            cost and expense, covenants and warrants to promptly investigate,
            clean up, remove, restore and otherwise remediate (including,
            without limitation, preparation of any feasibility studies or
            reports and the performance of any and all closures) any spill,
            release, discharge, disposal, emission, migration or transportation
            of Hazardous Materials arising from or related to the intentional or
            negligent acts or omissions of Tenant or Tenant's employees, agents,
            contractors or representatives such that the affected portions of
            the Premises, Equipment Space, Building, Property and any adjacent
            property are returned to the condition existing prior to the
            appearance of such Hazardous Materials. Any such investigation,
            clean up, removal, restoration and other remediation shall only be
            performed after Tenant has obtained Landlord's prior written
            consent, which consent shall not be unreasonably withheld so long as
            such actions would not potentially have a material adverse long-term
            or short-term effect on any portion of the Premises, Equipment
            Space, the Building, or the Property. Notwithstanding the foregoing,
            Tenant shall be entitled to respond immediately to an emergency
            without first obtaining Landlord's prior written consent. Tenant, at
            its sole cost and expense, shall conduct and perform, or cause to be
            conducted and performed, all closures as required by any
            Environmental Laws or any agencies or other governmental authorities
            having jurisdiction thereof. If Tenant fails to so promptly
            investigate, clean up, remove, restore, provide closure or otherwise
            so remediate, Landlord may, but without obligation to do so, take
            any and all steps necessary to rectify the same and Tenant shall
            promptly reimburse Landlord, upon demand, for all costs and expenses
            to Landlord of performing investigation, clean up, removal,
            restoration, closure and remediation work. All such work undertaken
            by Tenant, as required herein, shall be performed in such a manner
            so as to enable Landlord to make full economic use of the Premises,
            Equipment Space, the Building and Property, and after the
            satisfactory completion of such work.

      (e)   Environmental Indemnity. In addition to Tenant's obligations as set
            forth hereinabove, to the fullest extent permitted under applicable
            law, Tenant agrees to, and shall, protect, indemnify, defend (with
            counsel reasonably acceptable to Landlord) and hold Landlord and,
            Landlord's Related Parties harmless from and against any and all
            claims, judgments, damages, penalties, fines, liabilities, losses
            (including, without limitation, diminution in value of any portion
            of the Premises, Equipment Space, the Building, the Property,
            damages for the loss of or restriction on the use of rentable or
            usable space, and from any adverse impact of Landlord's marketing of
            any space within the Premises, Equipment Space, Building and/or
            Property), suits, administrative proceedings and costs (including,
            but not limited to, attorneys' and consultant fees and court costs)
            arising at any time during or after the Term of this Lease in
            connection with or related to, directly or indirectly, the use,
            presence, transportation, storage, disposal, migration, removal,
            spill, release or discharge of Hazardous Materials on, in or about
            any portion of the Premises, Equipment Space, the Building, or the
            Property as a result (directly or indirectly) of the acts or
            omissions of Tenant or any of Tenant's employees, agents, invitees,
            contractors or representatives. Neither the written consent of
            Landlord

                                       29
<PAGE>   33
            to the presence, use or storage of Hazardous Materials in, on, under
            or about any portion of the Premises, Equipment Space, the Building,
            and/or the Property, nor the strict compliance by Tenant with all
            Environmental Laws shall excuse Tenant and Tenant's officers and
            directors from its obligations of indemnification pursuant hereto.
            Tenant shall not be relieved of its indemnification obligations
            under the provisions of this Section 32(e) due to Landlord's status
            as either an "owner" or "operator" under any Environmental Laws.

      (f)   Survival. Tenant's obligations and liabilities pursuant to the
            provisions of this Article 32 shall survive the expiration or
            earlier termination of this Lease. If it is determined by Landlord
            that the condition of all or any portion of the Premises, Equipment
            Space, the Building, and/or the Property is not in compliance with
            the provisions of this Lease with respect to Hazardous Materials,
            including without limitation all Environmental Laws at the
            expiration or earlier termination of this Lease, then in Landlord's
            sole discretion, Landlord may require Tenant to hold over possession
            of the Premises and/or Equipment Space until Tenant can surrender
            the Premises and/or Equipment Space to Landlord in the condition in
            which the Premises and/or Equipment Space existed as of the
            Commencement Date and prior to the appearance of such Hazardous
            Materials except for reasonable wear and tear, including without
            limitation, the conduct or performance of any closures as required
            by any Environmental Laws. The burden of proof hereunder shall be
            upon Tenant. For purposes hereof, the term "reasonable wear and
            tear" shall not include any deterioration in the condition or
            diminution of the value of any portion of the Premises, Equipment
            Space, the Building, and/or the Property in any manner whatsoever
            related to directly, or indirectly, Hazardous Materials. Any such
            holdover by Tenant will be with Landlord's consent, will not be
            terminable by Tenant in any event or circumstance and will otherwise
            be subject to the provisions of this Lease.

      (g)   Landlord's Obligation. (i) Except as disclosed hereby or by Landlord
            making available to Tenant, for Tenant's review, Landlord's "Phase
            I" and "Phase II" environmental reports (if any) and environmental
            remediation plan (if any) or other environmental reports in
            Landlord's possession ("Environmental Reports"), Landlord
            represents, to the best of its knowledge, that the Premises,
            Equipment Space and other areas in which Tenant's equipment and
            cable may be located will be free of Hazardous Materials in amounts
            and conditions which violate applicable Environmental Laws, and,
            (ii) Landlord, at Landlord's sole cost and expense following notice
            of any violation, will cause the Premises and Equipment Space (as
            configured and improved as of, and in the condition existing as of,
            the date of this Lease) to be in full compliance with any and all
            current governmental conditions and requirements including but not
            limited to those relating to asbestos, PCB's and other Hazardous
            Materials, subject to Tenant's obligations as set forth above
            regarding Tenant's acts or omissions in or about the Building or
            Property. Landlord, at Tenant's request, will make available all
            Environmental Reports to Tenant.

      (h)   Landlord's Environmental Indemnity. Landlord shall, indemnify,
            defend and hold harmless Tenant from and against any and all losses,
            claims, suits and damages incurred by Tenant as a result of the
            presence, use, generation, storage, release or disposal of Hazardous
            Materials on, under or in the Building or the Property in violation
            of applicable Environmental Laws to the extent resulting from the
            act or negligent omission of Landlord.

33.   MISCELLANEOUS.

      (a)   Governing Law. This Lease and the rights and obligations of the
            parties shall be interpreted, construed and enforced in accordance
            with the Laws of the state in which the Building is located and
            Landlord and Tenant hereby irrevocably consent to the jurisdiction
            and proper venue of such state. If any term or provision of this
            Lease shall to any extent be invalid or unenforceable, the remainder
            of this Lease shall not be affected, and each provision of this
            Lease shall be valid and enforced to the fullest extent permitted by
            Law. The headings and titles to the Articles and Sections of this
            Lease are for convenience only and shall have no effect on the
            interpretation of any part of the Lease.

                                       30
<PAGE>   34
      (b)   Memorandum of Lease. Tenant shall not record this Lease or any
            memorandum.

      (c)   Waiver of Jury Trial. Landlord and Tenant hereby waive any right to
            trial by jury in any proceeding based upon a breach of this Lease.

      (d)   Force Majeure. Whenever a period of time is prescribed for the
            taking of an action by Landlord or Tenant, the period of time for
            the performance of such action shall be extended by the number of
            days that the performance is actually delayed due to fire,
            windstorm, flood, explosion, collapse of structures, governmental
            preemption or prescription, unavailability of utilities, strikes,
            acts of God, shortages of labor or materials, war, civil
            disturbances and other causes beyond the reasonable control of the
            performing party ("Force Majeure"). However, events of Force Majeure
            shall not extend or delay any date or period of time for the payment
            of Rent or other sums payable by either party or any period of time
            for the written exercise of an option or right by either party.

      (e)   Brokers. Tenant represents that it has dealt directly with and only
            with the Broker(s) described in Article 1 as a broker in connection
            with this Lease. Tenant shall indemnify and hold Landlord and the
            Landlord Related Parties harmless from all claims of any other
            brokers claiming to have represented Tenant in connection with this
            Lease. Landlord agrees to indemnify and hold Tenant and the Tenant
            Related Parties harmless from all claims of any brokers claiming to
            have represented Landlord in connection with this Lease. Landlord
            shall pay a commission to Broker(s) pursuant to a separate
            agreement.

      (f)   Authorizations, Etc. Tenant covenants, warrants and represents that:
            (1) each individual executing, attesting and/or delivering this
            Lease on behalf of Tenant is authorized to do so on behalf of
            Tenant; (2) this Lease is binding upon Tenant; and (3) Tenant is
            duly organized and legally existing in the state of its organization
            and is qualified to do business in the state in which the Premises
            are located. If there is more than one Tenant, or if Tenant is
            comprised of more than one party or entity, the obligations imposed
            upon Tenant shall be joint and several obligations of all the
            parties and entities. Notices, payments and agreements given or made
            by, with or to any one person or entity shall be deemed to have been
            given or made by, with and to all of them.

      (g)   Time of Essence. Time is of the essence with respect to Tenant's
            exercise of any expansion, renewal or extension rights granted to
            Tenant (if any). This Lease shall create only the relationship of
            landlord and tenant between the parties, and not a partnership,
            joint venture or any other relationship. This Lease and the
            covenants and conditions in this Lease shall inure only to the
            benefit of and be binding only upon Landlord and Tenant and their
            permitted successors and assigns.

      (h)   Survival. The expiration of the Term, whether by lapse of time or
            otherwise, shall not relieve either party of any obligations which
            accrued prior to or which may continue to accrue after the
            expiration or early termination of this Lease.

      (i)   No Offer. Landlord has delivered a copy of this Lease to Tenant for
            Tenant's review only, and the delivery of it does not constitute an
            offer to Tenant or an option. This Lease shall not be effective
            against any party hereto until an original copy of this Lease has
            been signed and delivered by such party.

      (j)   Integration. All understandings and agreements previously made
            between the parties are superseded by this Lease, and neither party
            is relying upon any warranty, statement or representation not
            contained in this Lease. This Lease may be modified only by a
            written agreement signed by Landlord and Tenant.

      (k)   Graphics. Tenant shall have the right to (i) one listing in the
            Building's directory on the ground floor lobby, to be provided by
            Landlord using the Building's standard lettering and (ii) one
            Building

                                       31
<PAGE>   35
            standard entry sign on or adjacent to the entrance to the Premises,
            to be provided at Tenant's expense.

      (l)   Financial Information. Tenant, within fifteen (15) days after
            request by Landlord, shall provide Landlord with a current financial
            statement and such other information as Landlord may reasonably
            request. Landlord shall use reasonable efforts to maintain such
            information as confidential.

      (m)   Standard for Consent. Except where expressly stated herein to the
            contrary, wherever the consent of Landlord or Tenant is required
            hereunder, the consent of such parties shall not be unreasonably
            withheld, delayed or conditioned. Whenever any act is required to be
            done by a party hereto to the satisfaction of or satisfactory to the
            other party or upon the request or requirement of the other party,
            the other party shall not unreasonably request or require such
            action by the performing party or decline to express is satisfaction
            therewith. Except as expressly set forth in this Lease, whenever a
            party's judgment is specified as the required standard or a party is
            permitted to exercise its discretion, such judgment and discretion
            shall be reasonably exercised.

      (n)   Confidentiality.

            (i)   Landlord shall use reasonable efforts to keep all Confidential
                  Information of Tenant (defined below) confidential; as used
                  herein "Confidential Information of Tenant' shall mean any
                  data or information pertaining to Tenant or Tenant's business,
                  regardless of medium that is provided by Tenant to Landlord,
                  including Tenant's plans and specifications or electrical
                  power requirements, site plans, or copies of any such
                  information but shall exclude any information (a) approved in
                  writing by Tenant for release to third parties, (b) that
                  Landlord possess independently of Tenant, (c) that Tenant
                  places in the public domain or (d) except as may be approved
                  in writing by Tenant for release to third parties or as may be
                  required by applicable law or as Landlord may, in Landlord's
                  good faith business judgment, disclose in confidence to
                  Landlord's employees, partners, counsel, lenders, or
                  investors, contractors, engineers, architects, project
                  managers or other similar individuals or entities in the
                  course of the operation of the Building and Property.

            (ii)  Tenant agrees to use diligent efforts to keep confidential the
                  terms and conditions of this Lease, and not to disclose (or
                  allow Tenant's employees, representatives or brokers
                  (including Tenant's Broker) to disclose) the terms and
                  conditions of this Lease to any third parties except as may be
                  approved in writing by Landlord for release to third parties
                  or as may be required by applicable law, as reasonably
                  determined by Tenant, or as Tenant may, in Tenant's good faith
                  business judgment, disclose in confidence to Tenant's counsel,
                  lenders, or investors. The violation of this provision by
                  Tenant or Tenant's employees, representatives or brokers
                  shall, at Landlord's option, be an incurable default under
                  this Lease.

                                       32
<PAGE>   36
34.   ENTIRE AGREEMENT.

      This Lease and the following exhibits and attachments constitute the
      entire agreement between the parties and supersede all prior agreements
      and understandings related to the Premises, including all lease proposals,
      letters of intent and other documents:

      EXHIBIT A (Outline and Location of Premises and Landlord's Conduits)
      EXHIBIT B (INTENTIONALLY OMITTED)
      EXHIBIT C (Description of Property)
      EXHIBIT D (Rules and Regulations)
      EXHIBIT E (Commencement Letter)
      EXHIBIT F (HazMat Certificate)
      EXHIBIT G (Tenant Options)
      EXHIBIT H (Form of Landlord Consent and Subordination Agreement)

      Landlord and Tenant have executed this Lease as of the day and year first
      above written.

                                LANDLORD:  CARLYLE-CORE CHICAGO LLC
                                           A DELAWARE LIMITED LIABILITY COMPANY

                                    By:  /s/ Fred Ezra
                                         -------------------------------------
                                    Name:  Fred Ezra
                                         -------------------------------------
                                    Title: Manager
                                         -------------------------------------

                                TENANT:    NET 2000 COMMUNICATIONS, INC.,
                                           a Delaware corporation

                                    By:  /s/ MA Mendez
                                         -------------------------------------
                                    Name:  MA Mendez
                                         -------------------------------------
                                    Title: COO & Secretary
                                         -------------------------------------

                                    By:  /s/ James W. Mores
                                         -------------------------------------
                                    Name:  James W. Mores
                                         -------------------------------------
                                    Title: AVP of RE
                                         -------------------------------------

                                           33
<PAGE>   37
                                    EXHIBIT A

                              LOCATION OF PREMISES

                                       AND

                               LANDLORD'S CONDUITS

                               EXHIBIT A - Page 1

<PAGE>   38
                                   EXHIBIT A
                              LOCATION OF PREMISES

                             [GRAPHIC OF FLOORPLAN]
<PAGE>   39
                                   EXHIBIT A
                              LOCATION OF PREMISES

                  [GRAPHIC OF FLOORPLAN WITH LANDLORD CONDUIT]
<PAGE>   40
                                    EXHIBIT B
                                 EQUIPMENT SPACE
                             [INTENTIONALLY OMITTED]

                                 EXHIBIT B-Page 1
<PAGE>   41
                                    EXHIBIT C

                                    PROPERTY

CALUMET PLANT:

PARCEL l:

Lots 1, 2, 3, 4, 5, 6, 7, 8, and 9 in Gurley and Keith's subdivision of block 23
in assessor's division of the southwest fractional 1/4 of section 22, township
39 north, range 14, east of the third principal meridian, in Cook County,
Illinois.

PARCEL 2:

All that vacated part of the intersection of East Cermak Road and South Park
Avenue, described as follows: beginning at a point on the south line of lot 9
produced east across the entrance of a vacated alley to the southwesterly line
of the right of way of the I.C. R.R. Company in Gurley and Keith's subdivision
of block 23 in assessor's division of the southwest fractional 1/4 of section
22, township 39 north, range 14, east of the third principal meridian, 13 feet
west of the southwesterly line of the right of way of the I.C. R.R. Company;
thence east on said line to the southwesterly line of the right of way of the
I.C. R.R. Company; thence southeasterly on the last described line a distance of
40 feet; thence northwesterly on a straight line to the point of beginning; in
Cook County, Illinois.

PARCEL 3:

The northwesterly and southeasterly 30 feet wide vacated alley lying
northeasterly and adjoining the northeasterly line of lots 1 to 9, both
inclusive, in Gurley & Keith's subdivision of block 23 in assessor's division of
the southwest fractional 1/4 of section 22, township 39 north, range 14, east of
the third principal meridian, and lying southwesterly of and adjoining the
southwesterly line of the right of way of the I.C. R.R. Company, in Cook County,
Illinois.

PARCEL 4:

All that part of the south 1/2 of vacated East 21st Street lying north and
adjoining the north line of lot 1 in Gurley & Keith's subdivision of block 23 in
assessor's division aforesaid, produced east to the southwesterly right of way
line of the I.C. R.R. Company; lying southwesterly and adjoining the
southwesterly right of way line of the I.C. R.R. Company and lying southeasterly
of and adjoining a line drawn from a point on the southwesterly line of the
right of way of the I.C. R.R. Company, 5 feet southerly of the south line of lot
9 in block 6 of George Smith's addition to Chicago in the southwest fractional
1/4 of section 22, township 39 north, range 14, east of the third principal
meridian, to the northeast corner of lot 1 in Gurley & Keith's subdivision of
block 23 in assessor's division of the southwest fractional 1/4 of section 22,
township 39 north, range 14, east of the third principal meridian, in Cook
County, Illinois.

PARCEL 5:

The south 1/2 of vacated East 21st Street lying east of the east line of Calumet
Avenue and west of parcel no. 4 above described, all in Cook County, Illinois.

                               EXHIBIT C-Page 1
<PAGE>   42
PARCEL 6:

The north 1/2 of vacated East Cermak Road lying south of and adjoining the south
line of lot 9 in Gurley & Keith's subdivision of block 23 in assessor's division
aforesaid, produced east to the southwesterly right of way line of the I.C. R.R.
Company (except that part described as parcel no. 2 above), all in Cook County,
Illinois.

TRUCK LOT D:

PARCEL 1:

Lots 5, 6, 7, 8 and 9 in block 6 in George Smith's addition to Chicago of a
subdivision of blocks 17 to 22 in assessor's division of the south west
fractional 1/4 of section 22, township 39 north, range 14 east of the third
principal meridian, in Cook County, Illinois.

PARCEL 2:

The north 1/2 of vacated East 21st Street lying south of and adjoining parcel 1
aforesaid and lying southwesterly of and adjoining the southwesterly right of
way line of the Illinois Central Railroad.

                               EXHIBIT C-Page 2
<PAGE>   43
                                    EXHIBIT D

                         BUILDING RULES AND REGULATIONS

        The following rules and regulations shall apply, where applicable, to
the Premises, the Building, the parking garage (if any), the Property and the
appurtenances. Capitalized terms have the same meaning as defined in the Lease.

1.      Sidewalks, doorways, vestibules, halls, stairways and other similar
        areas shall not be obstructed by Tenant or used by Tenant for any
        purpose other than ingress and egress to and from the Premises. No
        rubbish, litter, trash, or material shall be placed, emptied, or thrown
        in those areas. At no time shall Tenant permit Tenant's employees to
        loiter in Common Areas or elsewhere about the Building or Property.

2.      Plumbing fixtures and appliances shall be used only for the purposes for
        which designed, and no sweepings, rubbish, rags or other unsuitable
        material shall be thrown or placed in the fixtures or appliances. Damage
        resulting to fixtures or appliances by Tenant, its agents, employees or
        invitees, shall be paid for by Tenant, and Landlord shall not be
        responsible for the damage.

3.      No signs, advertisements or notices shall be painted or affixed to
        windows, doors or other parts of the Building, except those of such
        color, size, style and in such places as are first approved in writing
        by Landlord as specifically provided for in the Lease.

5.      Landlord will be provided with keys to the Premises.

6.      All contractors, contractor's representatives and installation
        technicians performing work in the Building shall be subject to
        Landlord's prior approval and shall be required to comply with
        Landlord's standard rules, regulations, policies and procedures, which
        may be revised from time to time.

7.      Tenant shall not: (1) make or permit any improper, objectionable or
        unpleasant noises or odors in the Building, or otherwise interfere in
        any way with other tenants or persons having business with them; (2)
        solicit business or distribute, or cause to be distributed, in any
        portion of the Building, handbills, promotional materials or other
        advertising; or (3) conduct or permit other activities in the Building
        that might, in Landlord's sole opinion, constitute a nuisance.

8.      No animals, except those assisting handicapped persons, shall be brought
        into the Building or kept in or about the Premises.

9.      Tenant shall not use or occupy the Premises in any manner or for any
        purpose which might injure the reputation or impair the present or
        future value of the Premises or the Building. Tenant shall not use, or
        permit any part of the Premises to be used, for lodging, sleeping or for
        any illegal purpose.

10.     Tenant shall not install, operate or maintain in the Premises or in any
        other area of the Building, electrical equipment that would overload the
        electrical system beyond its capacity for proper, efficient and safe
        operation as determined solely by Landlord.

11.     Tenant shall not operate or permit to be operated a coin or token
        operated vending machine or similar device (including, without
        limitation, telephones, lockers, toilets, scales, amusement devices and
        machines for sale of beverages, foods, candy, cigarettes and other
        goods), except for machines for the exclusive use of Tenant's employees.

12.     Bicycles and other vehicles are not permitted inside the Building or on
        the walkways outside the Building, except in areas designated by
        Landlord.

                               EXHIBIT D-Page 1
<PAGE>   44
13.     Landlord may from time to time adopt systems and procedures for the
        security and safety of the Building, its occupants, entry, use and
        contents. Tenant, its agents, employees, contractors, guests and
        invitees shall comply with Landlord's systems and procedures. Subject to
        Landlord's security procedures, access shall be permitted three hundred
        sixty-five (365) days a year, twenty-four (24) hours a week.

14.     Landlord shall have the right to prohibit the use of the name of the
        Building or any other publicity by Tenant that in Landlord's sole
        opinion may impair the reputation of the Building or its desirability.
        Upon written notice from Landlord, Tenant shall refrain from and
        discontinue such publicity immediately.

15.     Tenant shall not canvass, solicit or peddle in or about the Building or
        the Property.

16.     Neither Tenant nor its agents, employees, contractors, guests or
        invitees shall smoke or permit smoking anywhere in the Building.

                               EXHIBIT D-Page 2
<PAGE>   45
                                    EXHIBIT E

                               COMMENCEMENT LETTER

                                    (EXAMPLE)

Date:

Tenant: Net2OOO Communications, Inc.

Address:

Re:     Commencement Letter with respect to that certain Lease dated as of
        ____________________, _______ by and between CARLYLE-CORE CHICAGO LLC, a
        Delaware limited liability company, as Landlord, and ___________________
        ______________, as Tenant, located at 350 East Cermak Road, Chicago,
        Illinois 60616.

Dear         :

In accordance with the terms and conditions of the above referenced Lease,
Tenant accepts possession of the Premises and agrees:

1.      The Commencement Date of the Lease is __________________;

2.      The Rent Commencement Date of the Lease is __________________;

3.      The Expiration Date of the Lease is __________________;

4.      The Rentable Square Footage of the Premises is __________________;

5.      The Rentable Square Footage of the Equipment Space is ________________;

6.      Tenant's Pro Rata Share is __________________%;

7.      The schedule of Base Rent payable under the Lease is _________________;

8.      The schedule of Equipment Space rent payable under the Lease is
        __________________;

9.      The last day on which Tenant may exercise the Renewal Option is
        __________________, __________________.

Please acknowledge your acceptance of possession and agreement to the terms set
forth above by signing all 3 counterparts of this Commencement Letter in the
space provided and returning 2 fully executed counterparts to my attention.

Sincerely,

__________________________

                               EXHIBIT E-Page 1
<PAGE>   46
Agreed and Accepted:

        Tenant: _________________________________
        By:     _________________________________
        Name:   _________________________________
        Title:  _________________________________
        Date:   _________________________________

                               EXHIBIT E-Page 2
<PAGE>   47
                                    EXHIBIT F

                   HAZARDOUS MATERIALS DISCLOSURE CERTIFICATE

Your cooperation in this matter is appreciated. Initially, the information
provided by you in this Hazardous Materials Disclosure Certificate is necessary
for the Landlord (identified below) to evaluate and finalize a lease agreement
with you as tenant. After a lease agreement is signed by you and the Landlord
(the "Lease"), on an annual basis in accordance with the provisions of the
Lease, you are to provide an update to the information initially provided by you
in this certificate. The information contained in the initial Hazardous
Materials Disclosure Certificate and each annual certificate provided by you
thereafter will be maintained in confidentiality by Landlord subject to release
and disclosure as required by (i) any lenders and owners and their respective
environmental consultants, (ii) any prospective purchaser(s) of all or any
portion of the property on which the Premises are located, (iii) Landlord to
defend itself or its lenders, partners or representatives against any claim or
demand, and (iv) any laws, rules, regulations, orders, decrees, or ordinances,
including, without limitation, court orders or subpoenas. Any and all
capitalized terms used herein, which are not otherwise defined herein, shall
have the same meaning ascribed to such term in the signed Lease. Any questions
regarding this certificate should be directed to, and when completed, the
certificate should be delivered to:

Landlord:        CARLYLE-CORE CHICAGO LLC
                 c/o Core Location Realty Associates of Chicago, LLC
                 4520 East-West Highway, Suite 650
                 Bethesda, Maryland 20814
                 Attn: Mark Ezra

Name of Tenant:           NET2000 COMMUNICATIONS, INC.
                          2180 Fox Mill Road
                          Herndon, Virginia 20171
                          Attention: Legal Department

Contact Person, Title and Telephone Number(s): _________________________________

Contact Person for Hazardous Waste Materials Management and Manifests and
Telephone Number(s): ___________________________________________________________
________________________________________________________________________________
________________________________________________________________________________

Address of Premises: 350 East Cermak Road, Chicago, Illinois 60616

1.      GENERAL INFORMATION:

        Describe the initial proposed operations to take place in, on, or
about the Premises or Equipment Space, including, without limitation, principal
products processed, manufactured or assembled services and activities to be
provided or otherwise conducted. Existing tenants should describe any proposed
changes to on-going operations.

________________________________________________________________________________
________________________________________________________________________________

2.      USE, STORAGE AND DISPOSAL OF HAZARDOUS MATERIALS

        2.1    Will any Hazardous Materials be used, generated, stored or
disposed of in, on or about the Premises or Equipment Space? Existing tenants
should describe any Hazardous Materials which continue to be used, generated,
stored or disposed of in, on or about the Premises or Equipment Space.

        Wastes                     Yes / /                      No / /

                                EXHIBIT F-Page 1
<PAGE>   48
        Chemical Products          Yes / /                      No / /
        Other                      Yes / /                      No / /

                     If Yes is marked, please explain: _________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________

        2.2 If Yes is marked in Section 2.1, attach a list of any Hazardous
Materials to be used, generated, stored or disposed of in, on or about the
Premises or Equipment Space, including the applicable hazard class and an
estimate of the quantities of such Hazardous Materials at any given time;
estimated annual throughput; the proposed location(s) and method of storage
(excluding nominal amounts of ordinary household cleaners and janitorial
supplies which are not regulated by any Environmental Laws); and the proposed
location(s) and method of disposal for each Hazardous Material, including, the
estimated frequency, and the proposed contractors or subcontractors. Existing
tenants should attach a list setting forth the information requested above and
such list should include actual data from on-going operations and the
identification of any variations in such information from the prior year's
certificate.

3.      STORAGE TANKS AND SUMPS

        3.1 Is any above or below ground storage of gasoline, diesel, petroleum,
or other Hazardous Materials in tanks or sumps proposed in, on or about the
Premises or Equipment Space? Existing tenants should describe any such actual or
proposed activities.

                     Yes / /                            No / /

                     If yes, please explain: ___________________________________
________________________________________________________________________________
________________________________________________________________________________

4.      WASTE MANAGEMENT

        4.1 Has your company been issued an EPA Hazardous Waste Generator I.D.
Number? Existing tenants should describe any additional identification numbers
issued since the previous certificate.

                  Yes / /                            No / /

        4.2 Has your company filed a biennial or quarterly reports as a
hazardous waste generator? Existing tenants should describe any new reports
filed.

                  Yes / /                            No / /

                   If yes, attach a copy of the most recent report filed.

5.      WASTEWATER TREATMENT AND DISCHARGE

        5.1 Will your company discharge wastewater or other wastes to:

            ______ storm drain?       ______ sewer?
            ______ surface water?     ______ no wastewater or other wastes
                                                discharged.

                               EXHIBIT F-Page 2
<PAGE>   49
        Existing tenants should indicate any actual discharges. If so, describe
the nature of any proposed or actual discharge(s).
________________________________________________________________________________
________________________________________________________________________________

        5.2 Will any such wastewater or waste be treated before discharge?

                  Yes / /             No / /

                  If yes, describe the type of treatment proposed to be
conducted. Existing tenants should describe the actual treatment conducted.

________________________________________________________________________________
________________________________________________________________________________

6.      AIR DISCHARGES

        6.1 Do you plan for any air filtration systems or stacks to be used in
your company's operations in, on or about the Premises or Equipment Space that
will discharge into the air; and will such air emissions be monitored? Existing
tenants should indicate whether or not there are any such air filtration systems
or stacks in use in, on or about the Premises or Equipment Space which discharge
into the air and whether such air emissions are being monitored.

                  Yes / /             No / /

                  If yes, please describe: _____________________________________
________________________________________________________________________________
________________________________________________________________________________

        6.2 Do you propose to operate any of the following types of
equipment, or any other equipment requiring an air emissions permit? Existing
tenants should specify any such equipment being operated in, on or about the
Premises or Equipment Space.

            ______ Spray booth(s)      ______ Incinerator(s)
            ______ Dip tank(s)         ______ Other (Please describe)
            ______ Drying oven(s)      ______ No Equipment Requiring Air Permits

            If yes, please describe: ___________________________________________
________________________________________________________________________________
________________________________________________________________________________

7.      HAZARDOUS MATERIALS DISCLOSURES

        7.1 Has your company prepared or will it be required to prepare a
Hazardous Materials management plan ("Management Plan") pursuant to Fire
Department or other governmental or regulatory agencies' requirements? Existing
tenants should indicate whether or not a Management Plan is required and has
been prepared.

            Yes / /                   No / /

        If yes, attach a copy of the Management Plan. Existing tenants should
attach a copy of any required updates to the Management Plan.

                               EXHIBIT F-Page 3
<PAGE>   50
8.      ENFORCEMENT ACTIONS AND COMPLAINTS

        8.1 With respect to Hazardous Materials or Environmental Laws, has your
company ever been subject to any agency enforcement actions, administrative
orders, or consent decrees or has your company received requests for
information, notice or demand letters, or any other inquiries regarding its
operations? Existing tenants should indicate whether or not any such actions,
orders or decrees have been, or are in the process of being, undertaken or if
any such requests have been received.

            Yes / /                   No / /

            If yes, describe the actions, orders or decrees and any continuing
compliance obligations imposed as a result of these actions, orders or decrees
and also describe any requests, notices or demands, and attach a copy of all
such documents. Existing tenants should describe and attach a copy of any new
actions, orders, decrees, requests, notices or demands not already delivered to
Landlord pursuant to the provisions of Article 32 of the signed Lease.

________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________

         8.2 Have there ever been, or are there now pending, any lawsuits
against your company regarding any environmental or health and safety concerns?

            Yes / /                   No / /

            If yes, describe any such lawsuits and attach copies of the
complaint(s), cross-complaint(s), pleadings and all other documents related
thereto as requested by Landlord. Existing tenants should describe and attach a
copy of any new complaint(s), cross-complaint(s), pleadings and other related
documents not already delivered to Landlord pursuant to the provisions of
Article 32 of the Lease.

________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________

9.      PERMITS AND LICENSES

        9.1 Attach copies of all Hazardous Materials permits and licenses
including a Transporter Permit number issued to your company with respect to its
proposed operations in, on or about the Premises or Equipment Space, including,
without limitation, any wastewater discharge permits, air emissions permits, and
use permits or approvals. Existing tenants should attach copies of any new
permits and licenses, as well as any renewals of permits or licenses previously
issued.

The undersigned hereby acknowledges and agrees that this Hazardous Materials
Disclosure Certificate is being delivered in connection with, and as required
by, Landlord in connection with the evaluation and finalization of a Lease and
will be attached thereto as an exhibit; that this Hazardous Materials Disclosure
Certificate is being delivered in accordance with, and as required by, the
provisions of Article 32 of the Lease; and that Tenant shall have and retain
full and complete responsibility and liability with respect to any of the
Hazardous Materials disclosed in the HazMat Certificate notwithstanding
Landlord's receipt and/or approval of such certificate.

Tenant further agrees that none of the following described acts or events shall
be construed or otherwise interpreted as either (a) excusing, diminishing or
otherwise limiting Tenant from the requirement to fully and faithfully perform
its obligations under the Lease with respect to Hazardous Materials, including,
without limitation, Tenant's indemnification of the Landlord and all Landlord
Related Parties and compliance with all Environmental Laws, or (b) imposing upon
Landlord, directly or indirectly, any duty or liability with respect to any such
Hazardous Materials, including, without limitation, any duty on Landlord to
investigate or otherwise verify the accuracy of the representations and
statements made therein or to ensure that Tenant is in compliance with all
Environmental Laws: (i) the delivery of such certificate to Landlord and/or

                               EXHIBIT F-Page 4
<PAGE>   51
Landlord's acceptance of such certificate, (ii) Landlord's review and approval
of such certificate, (iii) Landlord's failure to obtain such certificate from
Tenant at any time, or (iv) Landlord's actual or constructive knowledge of the
types and quantities of Hazardous Materials being used, stored, generated,
disposed of or transported on or about the Premises or Equipment Space by Tenant
or Tenant's employees, agents, contractors or representatives. Notwithstanding
the foregoing or anything to the contrary contained herein, the undersigned
acknowledges and agrees that Landlord and its partners, lenders and
representatives may, and will, rely upon the statements, representations,
warranties, and certifications made herein and the truthfulness thereof in
entering into the Lease and the continuance thereof throughout the term, and any
renewals thereof, of the Lease.

I (print name) ______________________, acting with full authority to bind the
(proposed) Tenant and on behalf of the (proposed) Tenant, certify, represent and
warrant that the information contained in this certificate is true and correct.

TENANT:

By:     ________________________________

Title:  ________________________________

Date:   ________________________________

                               EXHIBIT F-Page 5
<PAGE>   52
                                    EXHIBIT G

                                 TENANT OPTIONS

1.      RENEWAL OPTION

        (a)     Generally. Tenant shall have the right to extend the Term (the
                "Renewal Option") for one (1) additional period of five (5)
                years ("Renewal Term") if:

                (i)     Landlord receives notice of exercise of the Renewal
                        Option ("Initial Renewal Notice") no earlier than
                        fifteen (15) full calendar months prior to the
                        expiration of the initial Term and no later than twelve
                        (12) full calendar months prior to the expiration of the
                        initial Term; and

                (ii)    Tenant is not in default under the Lease beyond the
                        applicable notice and cure period at the time that
                        Tenant delivers its Initial Renewal Notice or at the
                        time Tenant delivers its Binding Notice (as defined
                        below) or as of the Commencement of the Renewal Term;
                        and

                (iii)   The Premises or any portion thereof has not been sublet
                        (other than pursuant to a Permitted Transfer) at the
                        time that Tenant delivers its Initial Renewal Notice or
                        at the time Tenant delivers its Binding Notice; and

                (iv)    This Lease has not been assigned by Tenant (other than
                        pursuant to a Permitted Transfer) prior to the date that
                        Tenant delivers its Initial Renewal Notice or prior to
                        the date Tenant delivers its Binding Notice; and

                (v)     Tenant executes and returns the Renewal Amendment
                        (hereinafter defined) within thirty (30) days after
                        submission to Tenant of an accurate Renewal Amendment;
                        and

                (vi)    Tenant (or a transferee pursuant to a Permitted
                        Transfer) is in occupancy of all of the Premises at the
                        time Tenant delivers its Initial Renewal Notice, at the
                        time Tenant delivers its Binding Notice and as of the
                        commencement of the Renewal Term.

        (b)     Rent. The initial Base Rent rate and Equipment Space Rent rate
                during the Renewal Term shall equal the Prevailing Market
                (hereinafter defined) rate per Rentable Square Foot, as
                determined by Landlord, but in any event not less than the Base
                Rent rate and Equipment Space Rent rate payable by Tenant
                immediately prior to the commencement of the Renewal Term.

        (c)     Additional Rent. Tenant shall pay Additional Rent (i.e.
                Operating Expenses and Property Taxes) for the Premises during
                the Renewal Term in accordance with the Lease.

        (d)     Determination of Base Rent. Within thirty (30) days after
                receipt of Tenants Initial Renewal Notice, Landlord shall advise
                Tenant of the applicable Base Rent rate for the Premises and
                Equipment Space Rent rate for the Renewal Term. Tenant, within
                thirty (30) days after the date on which Landlord advises Tenant
                of the Base Rent rate and Equipment Space Rent rate for the
                Renewal Term, shall either (i) give Landlord final binding
                written notice ("Binding Notice") of Tenant's exercise of its
                option, or (ii) if Tenant disagrees with Landlord's
                determination, provide Landlord with written notice of rejection
                (the "Rejection Notice"). If Tenant falls to provide Landlord
                with either a Binding Notice or Rejection Notice within such
                thirty (30) day period, Tenants Renewal Option shall be null and
                void and of no further force and effect. If Tenant provides
                Landlord with a Binding Notice, Landlord and Tenant shall enter
                into the Renewal

                               EXHIBIT G-Page 1
<PAGE>   53
                Amendment (as defined below) upon the terms and conditions set
                forth herein. If Tenant provides Landlord with a Rejection
                Notice, Landlord and Tenant shall work together in good faith to
                agree upon the Prevailing Market Base Rent rate and Equipment
                Space Rent rate during the Renewal Term. Upon agreement,
                Landlord and Tenant shall enter into the Renewal Amendment in
                accordance with the terms and conditions hereof. Notwithstanding
                the foregoing, if Landlord and Tenant are unable to agree upon
                the Prevailing Market Base Rent rate and Equipment Space Rent
                rate for the Premises within thirty (30) days after the date on
                which Tenant provides Landlord with a Rejection Notice, then
                Tenant's Initial Renewal Notice and Tenant's exercise of the
                Renewal Option shall be null and void and of no further force or
                effect.

        (e)     Renewal Amendment. If Tenant is entitled to and properly
                exercises its Renewal Option, Landlord shall prepare an
                amendment (the "Renewal Amendment") to reflect changes in the
                Base Rent, Equipment Space Rent, Term, Expiration Date and other
                appropriate terms. The Renewal Amendment shall be:

                (i)     Sent to Tenant within a reasonable time after receipt of
                        the Binding Notice; and

                (ii)    Executed by Tenant and returned to Landlord in
                        accordance with Section 1.(a)(v) above.

                An otherwise valid exercise of the Renewal Option shall be fully
                effective whether or not the Renewal Amendment is executed.

        (f)     Prevailing Market. For purpose hereof, "Prevailing Market"
                shall mean the arms length fair market annual rent rate per
                rentable square foot under renewal leases and amendments for
                comparable space (if any), the Building entered into on or
                about the date on which the Prevailing Market is being
                determined hereunder for space comparable to the Premises and
                Equipment Space in the Building.

                               EXHIBIT G-Page 2

<PAGE>   54
                                    EXHIBIT H

              FORM OF LANDLORD CONSENT AND SUBORDINATION AGREEMENT

        This Landlord Consent and Subordination Agreement (this "Agreement") is
executed effective as of _______________________, by CARLYLE-CORE CHICAGO, LLC
(the "Landlord"), to and for the benefit of NORTEL NETWORKS INC., both in its
individual capacity and as agent for the Lenders (hereinafter defined) and as a
Lender under the Credit Agreement (hereinafter defined) (in each such capacity,
hereinafter called "Nortel Networks"), and the Lenders.

                                    RECITALS:

        A. Pursuant to that certain Lease dated _________________ 2000 (as
amended, supplemented, restated or replaced from time to time, the "Lease") by
and between the Landlord, as lessor, and NET2000 COMMUNICATIONS INC., as tenant
or lessee (the "Lessee"), the Landlord leased certain real property and related
interests (the "Premises"), to the Lessee, which Premises include approximately
______ square feet located on the second (2nd) floor of the Building located at
350 East Cermak Road, Chicago, Illinois 60606, the legal description of which is
attached hereto as Schedule A.

        B. Nortel Networks and Lessee are parties to that certain Master
Purchase Agreement dated as of November 2, 1998 (as amended, supplemented or
restated from time to time, the "Supply Agreement") pursuant to which Nortel
Networks has sold and/or will sell and Lessee has purchased and/or will purchase
certain equipment and services.

        C. Nortel Networks, individually as a lender and as administrative agent
for certain other lenders to be identified (collectively, including Nortel
Networks and the successors and assigns of such other lenders and Nortel
Networks, the "Lenders") and Lessee have entered into that certain Amended and
Restated Credit Agreement dated as of July 30, 1999 (as amended, modified,
supplemented, and/or restated from time to time, the "Amended Credit Agreement")
pursuant to which the Lenders have agreed to make loans and perhaps provide
other credit extensions to the Lessee to, among other things, finance Lessee's
purchase of equipment under the Supply Agreement (the "Equipment").

        D. All amounts at any time owned or owing by Lessee to Nortel Networks
under the Supply Agreement and all loans and other extensions of credit that may
be made by the Lenders to Lessee pursuant to the Credit Agreement are or would
be, respectively, secured by various assets, including, without limitation, the
Equipment and other personal property of the Lessee and Lessee and/or Nortel
Networks now or hereafter located on or about the Premises.

        E. Nortel Networks requires that this Agreement be executed by the
Landlord in connection with the Supply Agreement and the Credit Agreement.

        NOW, THEREFORE, in consideration of the Premises and or other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Landlord hereby covenants and agrees with Nortel Networks and
the Lenders as follows (notwithstanding anything to the contrary contained in
the Lease):

        1.      Subordination of Liens, etc.

                (a) All equipment (including, without limitation, the Equipment)
and other property of the Lessee and/or Nortel Networks from time to time
located on or about the Premises (the "Personal Property") is and shall remain
personal property of the Lessee and/or Nortel Networks, (as applicable, as the
Lessee and Nortel Networks may agree) and shall not become any part of the
Premises regardless of the manner of the affixation thereto, and Nortel Networks
and/or any Lender may at any time and from to time enter upon and otherwise have
access to the Premises to inspect, guard, maintain, prepare for sale, sell,
repossess and/or remove the Personal Property from the Premises in accordance
with the terms of this Agreement and/or the Lease, which sale, repossession,
and/or removal shall be free and clear of any lien, security interest, right or
claim ("Lien") which the Landlord may now or hereafter have, such right and
remedy of Nortel Networks and the Lenders being independent of any other right
or remedy Nortel Networks and/or any Lender may

                                EXHIBIT H-Page 1

<PAGE>   55
have, and the Landlord will not in any manner hinder, interfere or prevent any
of the foregoing if carried out in accordance with the terms of this Agreement.
Notwithstanding the foregoing consent of the Landlord (which consent shall not
be unreasonably withheld, conditioned or delayed), enter upon or otherwise have
access to the Premises for the foregoing purposes at any time after the
expiration of the Access Period. For purposes hereof, the term "Access Period"
shall mean:

                     (i) in the case of a termination of the Lease by Landlord
due to a default by Tenant thereunder, the period of time ending on the date
that is the later to occur of (A) thirty (30) days after the initial date upon
which the Lease is terminated and Nortel Networks (or any successor
"Administrative Agent" under the Credit Agreement) has received written notice
from the Landlord that such termination has occurred (which notice may not be
given prior to the date of termination of the Lease) or (B) the date upon which
the Landlord recovers possession of the Premises from the Lessee, whether by
eviction in accordance with the laws of the State of Illinois or the voluntary
surrender of possession of the Premises by the Lessee to the Landlord or

                     (ii) in the case of termination of the Lease due to
casualty or condemnation or due to the natural expiration of the Term of the
Lease, the period expiring as of the date of termination of the Lease. Nortel
Networks and the Lenders agree that they will, from time to time promptly after
any request by the Landlord to do so, reimburse the Landlord for any and all
damages directly caused by their removal of the Personal Property from the
Premises or repair such damages.

                (b) Any and all liens, security interests, rights and claims of
every kind (whether contractual, statutory or otherwise) which the Landlord may
now or hereafter have with respect to the Personal Property or any portion
thereof (collectively, the "Landlord's Liens"), and any and all rights or
remedies of every kind (whether contractual, statutory or otherwise) which the
Landlord may now or hereafter have to levy or distrain upon any Personal
Property or any interests therein or to claim or assert title to the Personal
Property or any portion thereof or to make any other claim against the Personal
Property or any portion thereof, are in each case hereby expressly made and
shall be subject and subordinate in every respect to any and all liens, security
interests, rights and claims and rights and remedies of every kind (whether
contractual, statutory or otherwise) which Nortel Networks and/or any Lender
may now or hereafter have with respect to the Personal Property or any portion
thereof (whether the same secure the indebtedness, liabilities and/or
obligations of the Lessee under the Supply Agreement and/or the Credit Agreement
or otherwise) (collectively, the "Nortel Networks Liens"), including, without
limitation, any rights to seize, hold, restrain, levy upon, take possession of,
Personal Property or proceeds thereof shall in all respects be senior to and
have priority over all Landlord's Liens in and to any Personal Property or
proceeds thereof irrespective of the time or order of the creation or
perfection of any Landlord's Liens.

                (c) If at any time the Landlord comes into possession or
control of any proceeds of any Personal Property, such proceeds shall be held
by the Landlord for the benefit of Nortel Networks and the Lenders, to the
extent of their interest therein, and the same shall forthwith be paid and
delivered to Nortel Networks.

        2.      Assignment of Lease, etc.

                (a) The Lessee shall be permitted, pursuant to the provisions of
the Lease, to transfer and assign all right, title and interest of the Lessee in
and to the Lease to Nortel Networks and/or the Lenders and/or their successor
and assigns and, in the event of any such transfer or assignment, and provided
Nortel Networks and/or the Lenders and/or their successors or assigns (as
applicable) expressly assume in writing and agree to perform each of the
Lessee's covenants, duties and obligations which will arise and accrue from and
after the date of such transfer or assignment, the Landlord agrees that it will
recognize Nortel Networks and/or the Lenders and/or their successors and assigns
(as applicable) as the successor(s)-in-interest to the Lessee under the Lease as
if Nortel Networks and/or the Lenders and/or their successors or assigns (as
applicable) were the Lessee under the Lease; provided, however, that the
Landlord shall not be obligated to recognize Nortel Networks or any Lender as
successor-in-interest to the Lessee under the Lease unless such
successor-in-interest is at least as credit worthy as was the Lessee as of the
initial date of the Lease.

                (b) The Landlord hereby (i) confirms the existence and validity
of the Lease, (ii) confirms that the Landlord is the owner and holder of the
Lease, (iii) confirms that, to the Landlord's current, actual knowledge, no
monetary default and no other default has occurred under the terms of the Lease,
(iv) agrees to provide Nortel Networks (or its

                               EXHIBIT H-Page 2
<PAGE>   56
successors or assigns), at its address specified below (or at the address of its
successors or assigns of which the Landlord is subsequently notified), a copy of
any notice of default delivered to the Lessee under the Lease substantially
concurrently with the delivery of such notice to the Lessee and (v) agrees that,
prior to the termination of the Lease as a result of a default of the Lessee
thereunder, the Landlord will provide written notice of such default to Nortel
Networks (or its successors or assigns) and the Lenders a period of time, after
notice of such default is given to Nortel Networks (or its successors or
assigns), equal to the applicable cure period specified in the Lease within
which to cure such default. For purposes of this Paragraph 2, the address of
Nortel Networks is as follows:

           Nortel Networks Inc.
           GMS 991 15 A4)
           2221 Lakeside Blvd.
           Richardson, Texas 75082-4399
           Attention:        Charles M. Helm, Esq.
           Telephone:        (972) 685-7839
           Telecopier:       (972) 684-3679

In addition, within fifteen business days after written request by Nortel
Networks (or its successors or assigns) or any Lender (which request may not
occur more than twice during any calendar year in the case of an estoppel
certificate or other instrument referred to in clause (A) succeeding), the
Landlord will execute and deliver in favor of Nortel Networks (or its successors
or assigns) and/or the Lenders (as may be requested) (A) an estoppel certificate
or other instrument in form reasonably acceptable to Nortel Networks (or its
successors or assigns) or such Lender (as applicable) pursuant to which the
Landlord will, as of the then current date, reconfirm each of the matters
referred to in clauses (i), (ii) and (iii) preceding (or specify any facts which
prevent any such reconfirmation) and (B) in the event that Nortel Networks (or
its successor or assigns) or any Lender has succeeded to the rights of the
Lessee under the Lease in accordance with Section 2(a) hereof, a new lease with
respect to the Premises in form and substance identical to the Lease, except
that such lease shall name Nortel Networks (or its successor or assigns) and/or
the Lenders (as may be requested) as lessee and the Landlord as lessor.

        3. No Obligation of Nortel Networks or Lenders. Nothing contained
herein shall be deemed or construed to obligate Nortel Networks or any Lender to
take any action hereunder or under to with respect to the Lease or to perform or
discharge any indebtedness, liability, obligation or duty of the Lessee under
the Lease.

        4. Successors and Assigns. This Agreement shall inure to the benefit of
Nortel Networks and the Lenders and their successors and assigns, including any
person or entity who shall have succeeded to Nortel Networks' or any Lender's
interest by, through or under judicial foreclosure or private sale or other
proceedings, or deed in lieu of foreclosure, or otherwise. Without limiting the
generality of the foregoing, all rights, remedies, benefits and privileges of
Nortel Networks under this Agreement shall insure to the benefit of the
"Administrative Agent" and the "Lenders", as such terms are defined in the
Credit Agreement, under the Credit Agreement, and all such rights, remedies,
benefits and privileges may, at any time, at the option of Nortel Networks and
without the necessity of any consent or approval of the Landlord or the Lessee,
be transferred or assigned to the "Administrative Agent" as such term is defined
in the Credit Agreement.

                               EXHIBIT H-Page 3
<PAGE>   57
Executed as of the date first above written.

                            LANDLORD:

                            CARLYLE-CORE CHICAGO LLC

                            By: __________________________________________
                            Name: ________________________________________
                            Title: _______________________________________

                            LESSEE:

                            NET 2000 COMMUNICATIONS

                            By: __________________________________________
                            Name: ________________________________________
                            Title: _______________________________________

State of ___________________)
                            )ss:
County of___________________)

        This instrument was acknowledged before me ______________________, 2000,
by _________________________ of ___________________, a ____________________, on
behalf of said entity.

                         _____________________________________________
                         Notary Public for the State of ______________

                         _____________________________________________
                         Print Name of Notary

My Commission Expires: ___________________

State of ___________________)
                            )ss:
County of___________________)

        This instrument was acknowledged before me ______________________, 2000,
by _________________________ of ___________________, a ____________________, on
behalf of said entity.

                         _____________________________________________
                         Notary Public for the State of ______________

                         _____________________________________________
                         Print Name of Notary

My Commission Expires: ___________________

                               EXHIBIT H-Page 4

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