Document:

<PAGE>

                                                                   EXHIBIT 10.33

                           THREE DULLES TECH CENTER

                                LEASE AGREEMENT

                                BY AND BETWEEN

                         DULLES TECH, INC, AS LANDLORD

                                      AND

                NETWORK ACCESS SOLUTIONS CORPORATION, AS TENANT

                               October 27, 1999
<PAGE>

                                LEASE AGREEMENT

                               TABLE OF CONTENTS

<TABLE>
<S>                                                                          <C>
ARTICLE I.  BASIC LEASE PROVISIONS

ARTICLE II.
     Section 2.1   Premises.................................................  1
     Section 2.2   Term.....................................................  2
     Section 2.3   Use......................................................  2

ARTICLE III.
     Section 3.1   Rental Payments..........................................  2
     Section 3.2   Additional Rent..........................................  3
     Section 3.3   Security.................................................  6
     Section 3.4   Tenant's Review Right....................................  7

ARTICLE IV.
     Section 4.1   Services.................................................  7
     Section 4.2   Keys and Locks...........................................  8
     Section 4.3   Graphics and Building Directory..........................  9

ARTICLE V.
     Section 5.1   Occupancy of Premises....................................  9
     Section 5.2   Entry for Repairs and Inspection.........................  9
     Section 5.3   Hazardous Materials......................................  9

ARTICLE VI.
     Section 6.1   Leasehold Improvements................................... 10
     Section 6.2   Repairs by Landlord...................................... 11
     Section 6.3   Repairs by Tenant........................................ 11
     Section 6.4   Liens.................................................... 12
     Section 6.5   Indemnification.......................................... 12

ARTICLE VII.
     Section 7.1   Condemnation............................................. 12
     Section 7.2   Force Majeure............................................ 13
     Section 7.3   Fire or Other Casualty Damage............................ 13
     Section 7.4   Insurance................................................ 14
     Section 7.5   Waiver of Subrogation Rights............................. 14

ARTICLE VIII.
     Section 8.1   Default by Tenant........................................ 15
     Section 8.2   Landlord's Remedies...................................... 15
     Section 8.3   Waiver of Duty to Relet or Mitigate...................... 16
     Section 8.4   Reentry.................................................. 17
     Section 8.5   Rights of Landlord in Bankruptcy......................... 17
     Section 8.6   Waiver of Certain Rights................................. 17
     Section 8.7   NonWaiver................................................ 17
     Section 8.8   Holding Over............................................. 17
     Section 8.9   Abandonment of Personal Property......................... 17

ARTICLE IX.
     Section 9.1   Transfers................................................ 17
     Section 9.2   Assignment by Landlord................................... 19
     Section 9.3   Limitation of Landlord's Liability....................... 19

ARTICLE X.
     Section 10.1  Subordination............................................ 19
</TABLE>
<PAGE>

<TABLE>
<S>                                                                          <C>
     Section 10.2  Estoppel Certificate or Three-Party Agreement............ 19
     Section 10.3  Notices.................................................. 20

ARTICLE XI.
     Section 11.1   Right to Relocate Tenant................................ 20
     Section 11.2   Rights and Remedies Cumulative.......................... 20
     Section 11.3   Legal Interpretation.................................... 20
     Section 11.4   Authority............................................... 21
     Section 11.5   No Brokers.............................................. 21
     Section 11.6   Consents by Landlord.................................... 21
     Section 11.7   Joint and Several Liability............................. 21
     Section 11.8   Independent Covenants................................... 21
     Section 11.9   Attorneys' Fees and Other Expenses...................... 21
     Section 11.10  Recording............................................... 21
     Section 11.11  Disclaimer; Waiver of Jury Trial........................ 21
     Section 11.12  Access to Roof.......................................... 22
     Section 11.13  Parking................................................. 22
     Section 11.14  No Accord or Satisfaction............................... 22
     Section 11.15  Acceptance.............................................. 22
     Section 11.16  Waiver of Counterclaim.................................. 22
     Section 11.17  Time Is of the Essence.................................. 22
     Section 11.18  Counterparts............................................ 22
</TABLE>

EXHIBITS

     Exhibit A - Land
     Exhibit B - Floor Plan(s) of Premises
     Exhibit C - Special Stipulations
     Exhibit D - Commencement Date
                    Agreement
     Exhibit E - Work Letter Agreement
     Exhibit F - Building Rules and Regulations
     Exhibit G - Proposed Tenant Signage
     Exhibit H - Cleaning Specifications
     Exhibit I - Parking Area
<PAGE>

                                LEASE AGREEMENT

THIS LEASE AGREEMENT (this "Lease") is made and entered into as of the 27th day
                            -----
of October, 1999, by and between DULLES TECH, INC., a Delaware corporation
("Landlord"), whose address is c/o West World Management, Inc., 4 Manhattanville
 ---------
Road, Purchase, New York 10577, and NETWORK ACCESS SOLUTIONS CORPORATION, a
Delaware corporation ("Tenant"), whose address is 100 Carpenter Drive, Suite
                       ------
206, Sterling, Virginia 20164, Attention:  Manager, Facilities.  Subject to all
of the terms, provisions, covenants and conditions of this Lease, and in
consideration of the mutual covenants, obligations and agreements contained in
this Lease, and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, Landlord and Tenant agree as
follows:

                                  ARTICLE I.

                            BASIC LEASE PROVISIONS

Landlord, for and in consideration of the rents and all other charges and
payments hereunder and of the covenants, agreements, terms, provisions and
conditions to be kept and performed hereunder by Tenant, demises and leases to
Tenant, and Tenant hereby hires and takes from Landlord, the premises described
below, subject to all matters hereinafter set forth and upon and subject to the
covenants, agreements, terms, provisions and conditions of this Lease for the
term hereinafter stated. For purposes of this Lease, the following terms shall
have the meanings ascribed to them below:

Base Year shall mean calendar year 2000.
---------

Building shall mean the approximately 113,093 rentable square foot structure
--------
situated upon the Land (hereinafter defined) commonly known as Three Dulles Tech
Center located at 13650 Dulles Technology Drive, Herndon, Virginia 20171, County
of Fairfax, State of Virginia as the same currently exists or as it may from
time to time hereafter be expanded or modified.

Commencement Date shall mean March 1, 2000, provided that the First Phase
-----------------
Premises are Substantially Complete (as defined in Exhibit E to this Lease).  In
the event the First Phase Premises are not Substantially Complete by March 1,
2000, the Commencement Date will be extended day for day until Landlord makes
the First Phase Premises Substantially Complete.

Land shall mean that certain tract of 12.14 acres of land situated in Fairfax
----
County, Virginia and more particularly described on Exhibit A attached hereto
and hereby made a part hereof.

Lease Year shall mean each consecutive twelve (12) month period during the Term
----------
commencing with the Commencement Date.

Prepaid Rent shall mean the amount of $227,822.63 for the first and a portion of
------------
the second month of the Term. Prepaid Rent shall be paid by Tenant to Landlord
no later than January 1, 2000.

Project shall mean the Building, together with the Land and the parking area
-------
serving the Building, all other improvements situated on the Land or directly
benefitting the Building, and all additional facilities or improvements directly
benefitting the Building that may be constructed in subsequent years.

Security Deposit shall mean the amount of $1,600,000 as shall be posted and
----------------
reduced during the Term of this Lease as set forth in Section 3.3.

Term shall mean One Hundred Twenty (120) months from the Commencement Date, as
----
the same may be extended pursuant to Section C of Exhibit C attached hereto.

                                  ARTICLE II.
<PAGE>

     Section 2.1  Premises.  The Premises demised by this Lease are deemed to be
                  --------
(i) 57,709 rentable square feet consisting of an approximately 10,397 rentable
square foot portion of the first floor, as shown on Exhibit B attached hereto,
                                                    ---------
and the entirety of Floors four and five of the Building (the "First Phase
                                                               -----------
Premises"); (ii) 46,022 rentable square feet known or to be known as Suites 200
--------
and 300, on Floors two and three, respectively, of the Building (with each Suite
occupying the entire floor) (the "Second Phase Premises"); and (iii) 9,362
                                  ---------------------
rentable square feet on the first floor of the Building, as shown on Exhibit B
attached hereto, which is to serve as a network and/or telecommunications
operations center or for similar use by Tenant (the "Third Phase Premises"),
                                                     --------------------
together with the nonexclusive use of the common areas of the Project made
available by Landlord from time to time to all tenants of the Project (the First
Phase Premises, the Second Phase Premises and the Third Phase Premises are
collectively referred to herein as the "Premises"). The Premises are outlined on
                                        --------
Exhibit B attached hereto and hereby made a part hereof.  All square footage
---------
utilized in this Lease has been or will be as to future space, made in
accordance with "Standard Method for Measuring Floor Area in Office Buildings",
published by the Secretariat, Buildings Owners and Managers Association
International (ANSI/BOMA Z65.1 - 1996), approved June 7, 1996 (the "Standard
                                                                    --------
Measure").  Unless otherwise specifically designated, all references to square
-------
footage or square feet in this Lease are to rentable square footage or square
feet. Landlord shall have its space planner or architect re-measure the Premises
upon completion of the Tenant Space Plan (as defined in Exhibit E) and/or
                                                        ---------
Tenant's Work (as defined in Exhibit E), and at no time thereafter, to confirm
                             ---------
that the measurement provided herein is accurate and conforms to the Standard
Measure. In the event that such re-measurement shows a different rentable square
footage for the Premises, all relevant terms of this Lease shall be adjusted to
conform to such re-measurement.

     Section 2.2  Term.  The Term of this Lease shall begin on the Commencement
                  ----
Date and shall continue in full force and effect for the Term of this Lease
unless extended or sooner terminated in accordance with the provisions of this
Lease.  After the occurrence of the Commencement Date, Tenant and Landlord shall
execute a certificate in the form attached as Exhibit D stipulating and agreeing
                                              ---------
to the Commencement Date.  If the Commencement Date should be changed for any
reason, including a change pursuant to the terms of Exhibit E hereto, Landlord
                                                    ---------
shall not be liable or responsible for any claims, damages or liabilities in
connection therewith or by reason thereof. If the First Phase Premises are not
Substantially Complete as of March 1, 2000 for any reason other than a Tenant
Delay, then the term Commencement Date shall mean such subsequent date upon
which the First Phase Premises are Substantially Complete, and such failure to
Substantially Complete the First Phase Premises on the earlier date shall not
constitute a default by Landlord hereunder or render Landlord liable for any
loss or damage that may be incurred as a result of such failure.

     Section 2.3  Use.  The Premises are to be used only for general office
                  ---
purposes, including but not limited to, use of a portion of the first floor of
the Building, to the extent permitted by law or covenant, as a network and/or
telecommunications operations center or related use and for no other business or
purpose without the prior written consent of Landlord which consent shall not be
unreasonably withheld or delayed. No act shall be done in or about the Premises
that is unlawful or that will increase the existing rate of insurance on the
Building. In the event of a breach of this covenant, Tenant shall, after written
notice, (a) immediately cease the performance of any unlawful act and (b) with
respect to acts that will or has increased the existing rate of insurance,
Tenant shall either cease such act that is increasing or has increased the
existing rate of insurance (and pay for any such increases theretofor charged to
Landlord) or shall pay to Landlord any and all increases in insurance premiums
resulting from such breach. Tenant shall not commit or allow to be committed any
waste upon the Premises, or any public or private nuisance or other act or thing
which disturbs the quiet enjoyment of any other tenant in the Building. If any
of Tenant's office machines or equipment disturb any other tenant in the
Building, then Tenant shall provide adequate insulation, or take such other
action as may be necessary to eliminate the noise or disturbance at its sole
cost and expense. Tenant shall not, without Landlord's prior consent which
consent shall not be unreasonably withheld or delayed, install any equipment,
machine, device, tank or vessel which is subject to any federal, state or local
permitting requirement. Tenant, at its expense, shall comply with all laws,
statutes, ordinances and governmental rules, regulations or requirements
governing the installation, operation and removal of any such equipment,
machine, device, tank or vessel. Tenant, at its expense, shall comply with all
laws, statutes, ordinances, governmental rules, regulations or
requirements, and the provisions of any recorded documents now existing or
hereafter in effect
<PAGE>

relating to its use, operation or occupancy of the Premises and shall observe
such reasonable and non-discriminatory rules and regulations as may be adopted
and made available to Tenant by Landlord from time to time for the safety, care
and cleanliness of the Premises or the Building and for the preservation of good
order therein; provided, however, that such rules and regulations do not
               --------  -------
conflict with this Lease, materially increase Tenant's obligations or liability
with respect to the Premises and to the extent such rules and regulations do
conflict with the terms of this Lease, the terms of this Lease shall govern. The
current rules and regulations for the Building are attached hereto as Exhibit F.
                                                                      ---------
Without limiting the foregoing, Tenant agrees to be wholly responsible at
Tenant's sole cost and expense for any accommodations or alterations which need
to be made to the Premises to comply with the provisions of the Americans With
Disabilities Act of 1990, as amended (the "ADA").  Landlord will be responsible
                                           ---
for compliance of the common areas of the Building as well as the Building shell
(as described in Exhibit E) with the provisions of ADA.

                                 ARTICLE III.

     Section 3.1  Rental Payments.
                  ---------------

     (a)  Base Rent.  Commencing (i) on the Commencement Date as to the First
          ---------
Phase Premises, (ii) on the date of Substantial Completion of the Second Phase
Premises (or such earlier date as the Second Phase Premises would have been
Substantially Complete but for Tenant Delays) as to the Second Phase Premises,
and (iii) on the earlier of July 1, 2000 or the date of Substantial Completion
of the Third Phase Premises as to the Third Phase Premises, and continuing
thereafter throughout the Term, Tenant shall pay the Base Rent, which is due and
payable each Lease Year during the Term hereof in twelve (12) equal installments
on the first (1st) day of each calendar month during the Term to Landlord at
Landlord's address specified in this Lease (or such other address as may be
designated by Landlord from time to time) monthly in advance at the following
rates:

<TABLE>
<CAPTION>
          Lease     Base Rent Per
          Year      Rentable Square Foot
          ----      --------------------
          <S>       <C>
          1          $ 25.50
          2          $ 25.94
          3          $ 25.95
          4          $ 25.94
          5          $ 25.50
          6          $ 25.50
          7          $ 25.50
          8          $ 25.50
          9          $ 25.50
          10         $ 25.50
</TABLE>

So long as Tenant is not then in default under this Lease, in the event Tenant
has paid Landlord any Prepaid Rent such Prepaid Rent shall be applied to the
first (1st) monthly and a portion of the second (2nd) installment of Base Rent
due hereunder.

     (b)  First Year Credit. Notwithstanding anything to the contrary in Section
          -----------------
3.1(a), Tenant shall receive a credit against the Base Rent payable during the
first year of the Term of the Lease in an aggregate amount of Twelve Thousand
Five Hundred and No/100's Dollars ($12,500.00) per month.

     (c)  Annual CPI Adjustment.  On each anniversary of the Commencement Date,
          ---------------------
the annual Base Rent for the entire Premises (but, for purposes of this
Subsection, excluding from the Base Rent in respect of the second, third and
fourth lease years, the sums per rentable square foot of $0.44, $0.45 and $0.44
respectively) shall be adjusted as follows:  beginning the first day of the
second lease year following the Commencement Date, the Base Rent shall be
increased by an amount equal to three hundred percent (300%) of any increase in
the CPI.  The amount of the adjustment shall be determined by multiplying the
previous year's adjusted Base Rent by a product of (a) three hundred percent
(300%) and (b) a fraction, the numerator of which shall be (i) the CPI for the
period immediately preceding the anniversary date of the lease year for which
the adjustment is to be made, minus (ii) the CPI for the period immediately
preceding the
<PAGE>

previous lease year, and the denominator of which shall be the CPI for the
period immediately preceding the previous lease year. Notwithstanding this
calculation, the adjustment to the Base Rent shall not exceed three percent (3%)
of the Base Rent for the immediately preceding Lease Year.

     The CPI as used herein shall mean the United States Bureau of Labor
Statistics, Consumer Price Index for Urban Consumers, all items for Washington,
D.C.-MD-VA (CPI-U) (1982 - 1984 = 100). If the CPI shall be discontinued with no
successor or comparable successor index, Landlord shall promptly so notify
Tenant and the parties shall attempt to agree within thirty (30) days after
Tenant's receipt of such notice upon a substitute index which measures, on at
least an annual basis, fluctuations in the cost of goods to consumers of such
goods in the Washington, D.C. metropolitan area. If the parties are unable to
agree upon a substitute index, then the matter shall be determined by
arbitration in accordance with the rules of the American Arbitration Association
then prevailing.

     (d)  Partial Month.  If the date for Tenant to start paying any of the
          -------------
amounts of Basic Rent set forth above is other than the first (1st) day of a
calendar month or if this Lease expires or terminates on a day other than the
last day of a calendar month, then the installments of Base Rent for such month
or months shall be prorated based upon multiplying the applicable Base Rent by a
fraction, the numerator of which shall be the number of days of the Term
occurring during said commencement or termination month, as the case may be, and
the denominator of which shall be the number of days in such month.

     (e)  Payment; Late Charge; Past Due Rate.  The Base Rent, the Additional
          -----------------------------------
Rent (hereinafter defined), any Prepaid Rent and any and all other payments
which Tenant is obligated to make to Landlord under this Lease shall constitute
and are sometimes hereinafter collectively referred to as "Rent". Tenant shall
pay all Rent and other sums of money as shall become due from and payable by
Tenant to Landlord in lawful money of the United States of America at the times
and in the manner provided in this Lease, without demand, deduction, abatement,
setoff, counterclaim or prior notice. Tenant hereby acknowledges that late
payment to Landlord of Rent or other sums due hereunder will cause Landlord to
incur costs not contemplated by this Lease, the exact amount of which will be
extremely difficult to ascertain. If any Rent or other sum due from Tenant is
not received on or before its due date, then Tenant shall pay to Landlord
immediately upon Landlord's demand therefor, in addition to such overdue amount,
a late charge in an amount equal to Five Thousand and No/100's Dollars ($5,000),
plus any reasonable attorneys' fees and costs incurred by Landlord by reason of
Tenant's failure to pay Rent and other charges when due hereunder; provided,
                                                                   --------
however, that Landlord shall waive such charge as to the first such instance in
-------
any Lease year (but in no event more than three (3) times during the Term of the
Lease) as to which such late charge would otherwise be payable. Additionally,
all Rent under this Lease shall bear interest from the date due until paid at
the lesser of twelve percent (12%) or the maximum nonusurious rate of interest
then permitted by the applicable laws of the state in which the Building is
located or the United States of America, whichever shall permit the higher
nonusurious rate, such interest being in addition to and cumulative of any other
rights and remedies which Landlord may have with regard to the failure of Tenant
to make any such payments under this Lease.

     Section 3.2  Additional Rent.
                  ---------------

     (a)  Definitions:
          -----------

          (i)  "Base Operating Expenses" means Operating Expenses (hereinafter
                -----------------------
defined) for the Base Year.

          (ii) "Operating Expenses" means all expenses, costs and disbursements
                ------------------
of every kind and nature, provided such expenses, costs and disbursements are
actually incurred, relating to or incurred or paid in connection with the
ownership and operation of the Project, computed on an accrual basis in
accordance with generally accepted accounting principles consistently applied,
including but not limited to the following:

               (A)  the proportionate share of wages and salaries of all persons
directly engaged in the operation, maintenance, security or access control of
the Project, including all
<PAGE>

taxes, insurance and benefits relating thereto, provided that no such amounts
are allowed for any employee above the level of property engineer;

               (B)  the cost of all supplies, tools, equipment and materials
used in the operation and maintenance of the Project, including rental fees for
the same, if such items are not purchased and amortized pursuant to this Section
                                                                         -------
3.2 below;
---

               (C)  the cost of all utilities for the Project, including but not
limited to the cost of water and power, heating, lighting, air conditioning and
ventilating (excluding those costs billed to specific tenants) of the Building
and Project;

               (D)  the cost of all maintenance and service agreements for the
Project and the equipment therein, including but not limited to alarm service,
security service, access control, landscaping, window cleaning, pest control,
elevator maintenance and janitorial service;

               (E)  the cost of repairs and general maintenance, excluding (y)
repairs and general maintenance paid by proceeds of insurance, by Tenant or by
other third parties, and (z) alterations attributable solely to tenants of the
Building;

               (F)  amortization (at an interest rate of 8% per annum) of the
cost of capital investment items which are installed for the purpose of reducing
operating expenses, promoting safety, complying with governmental requirements
or maintaining the quality of the Building over the useful life of such item;

               (G)  the cost of all insurance relating to the Project,
including, but not limited to, the cost of property insurance, casualty, rental
loss and liability insurance applicable to the Project and Landlord's personal
property used in connection therewith and the cost of commercially reasonable
deductibles paid on claims made by Landlord;

               (H)  Landlord's and/or Landlord's managing agent's reasonable
accounting and audit costs and attorneys' fees applicable to the Project;

               (I)  all property management fees for the Project, provided that
such fees shall not exceed three percent (3%) of gross receipts for the Project;
and

               (J)  all taxes, assessments and governmental charges, whether or
not directly paid by Landlord, whether federal, state, county or municipal and
whether they are imposed by taxing districts or authorities currently taxing the
Project or by others subsequently created or otherwise, and any other taxes and
assessments, assessed against or attributable to the Project or its operation,
excluding, however, (i) federal and state taxes on income, death taxes,
---------  -------
franchise taxes and any taxes imposed or measured on or by the income of
Landlord from the operation of the Project, (ii) transfer taxes or fees imposed
in connection with any change of ownership of the Project together with the
reasonable cost (including attorneys, consultants and appraisers) of any
negotiation, contest or appeal pursued by Landlord in an effort to reduce any
such tax, assessment or charge, and all of Landlord's administrative costs in
relation to the foregoing ("Real Estate Taxes"); provided, however, that if at
                            -----------------    --------  -------
any time during the Term the present method of taxation or assessment shall be
so changed that the whole or any part of the taxes, assessments, levies,
impositions or charges now levied, assessed or imposed on real estate and the
improvements thereof shall be changed and as a substitute therefor, or in lieu
of or in addition thereto, taxes, assessments, levies, impositions or charges
shall be levied, assessed or imposed wholly or partially as a capital levy or
otherwise on the rents received from the Project or the rents reserved herein or
any part thereof, then such substitute or additional taxes, assessments, levies,
impositions or charges, to the extent so levied, assessed or imposed, shall be
deemed to be included within the Real Estate Taxes to the extent that such
substitute or additional tax would be payable if the Project were the only
property of the Landlord subject to such tax, (iii) any environment assessments,
charges or liens arising in connection with the remediation of Hazardous
Materials from the Project, the causation of which arose prior to the
Commencement Date or was caused by Landlord, its agents, employees or
contractors or any tenant of the Project (other than Tenant or its sublessees or
assignees), (iv) costs or fees payable to public authorities in connection with
any future construction, renovation and/or improvements to the Project other
than Tenant's Work, including fees for transit, housing, schools, open space,
<PAGE>

child care, arts programs, traffic mitigation measures, environmental impact
reports, traffic studies, and transportation system management plans or (v)
reserves for future taxes.

     Notwithstanding the foregoing provisions of this Section 3.2(a)(ii),
                                                      ------------------
Operating Expenses shall not include any of the following:

     (A)  legal fees, brokerage commissions, advertising costs or related
expenses in connection with the leasing of the Project and/or administration of
Landlord's ownership entity;

     (B)  except as allowable under Section 3.2(a)(ii)(F), capital repairs,
                                    ---------------------
alterations, additions, improvements or replacements connected with or arising
from the renovation of the Project or any repairs or replacements made to
rectify or correct any defect in the design, materials or workmanship of any
portion of the Project or Commons Areas;

     (C)  costs incurred in connection with damage or repairs which are covered
under any insurance policy carried by Landlord in connection with the Project or
Common Areas (except for commercially reasonable deductibles);

     (D)  expenses for repair or replacement paid by condemnation awards;

     (E)  costs associated with damage or repairs to the Project or the Common
Areas necessitated by the gross negligence or willful misconduct of Landlord or
Landlord's employees, agents, contractors or invitees;

     (F)  increases in insurance premiums over those in effect on the
Commencement Date to the extent any other tenant causes Landlord's insurance
premiums to increase or obligates Landlord to purchase additional insurance;

     (G)  reserves for Landlord's repair, replacement or improvement of the
Project or any portion thereof;

     (H)  charitable or political contributions or fees paid to trade
associates;

     (I)  Landlord's general overhead expenses not related to the Project or
Common Areas;

     (J)  all principal, interest, loan fees, and other carrying costs related
to any mortgage or deed of trust encumbering the Project and all rental and
other payables due under any ground or underlying lease;

     (K)  legal fees, accountant fees and other expenses incurred in disputes
with other tenants or occupants of the Project or associated with the
enforcement of any other leases or defense of Landlord's title to or interest in
the Project or any part thereof;

     (L)  costs (including permit, license and inspection fees) incurred in
renovating or otherwise improving, decorating, painting, expanding or altering
space for other tenants or other occupants of vacant space in the Project;

     (M)  any costs, fines, or penalties incurred due to violations by Landlord
or any tenant of the Project (other than Tenant) of any governmental rule or
authority, this Lease or any other lease in the Project, or due to Landlord's
gross negligence or willful misconduct;

     (N)  payments for rented equipment, the cost of which equipment would be a
capital expenditure if such equipment were purchased by Landlord;

     (O)  the cost of any special service provided to Tenant or other occupants
of the Project for which Landlord is entitled, pursuant to the terms of leases,
to be reimbursed;

     (P)  the costs of major repairs and/or replacements of the roof,
foundation, and structural supports of the Premises unless such costs are
amortized over the useful life of the item;
<PAGE>

     (Q)  any amounts paid to any person, firm or corporation related to or
otherwise affiliated with Landlord or any general partner, officer, director or
shareholder of Landlord or any of the foregoing, to the extent the same exceeds
arm's length competitive prices paid in Fairfax County, Virginia for similar
services or goods; and

     (R)  costs of acquisition of sculpture or other objects of art for the
Project.

     Operating Expenses shall be reduced by all cash discounts, trade discounts
or quantity discounts received by Landlord or Landlord's managing agent in the
purchase of any goods, utilities or services in connection with the prudent
operation of the Building. In the calculation of any expenses hereunder, it is
understood that no expense shall be charged more than once. Landlord shall use
its reasonable efforts in good faith to effect an equitable proration of bills
for services rendered to the Building and to any other property owned by
Landlord or an affiliate of Landlord.

     Landlord agrees that, upon Tenant's request from time to time, Landlord
shall confer with Tenant to consider mutually acceptable ways to minimize or
reduce Operating Expenses.

          (iii)  "Adjustment Period" means each calendar year occurring during
                  -----------------
the Term beginning with calendar year 2001, which shall be the first Adjustment
Period.

          (iv)   "Tenant's Pro Rata Share" means the percentage calculated by
                  -----------------------
dividing the rentable area of the Premises (numerator) by the rentable area of
the Building (denominator), and expressing the fraction as a percentage.

     (b)  Gross-Up Adjustment. If the Building is less than fully occupied or if
          -------------------
standard Landlord services are not provided to the entire Building during the
Base Year or any Adjustment Period, then Operating Expenses for the Base Year or
such Adjustment Period shall be "grossed up" by Landlord to that amount of
Operating Expenses that, using reasonable projections, would normally be
expected to be incurred during the Base Year or Adjustment Period if the
Building was one hundred percent (100%) occupied and receiving building standard
Landlord services during the Base Year or Adjustment Period, as determined under
generally accepted accounting principles consistently applied.

     (c)  Payment by Tenant. If the Operating Expenses for any Adjustment Period
          -----------------
exceed the Base Operating Expenses (any such excess being known collectively as
the "Expense Increase"), then Tenant agrees to pay Landlord as additional rent
     ----------------
(the "Additional Rent") Tenant's Pro Rata Share of the Expense Increase;
      ---------------
provided, however, that notwithstanding any other provision of this Lease to the
--------  -------
contrary, no such payment with respect to excess Operating Expenses shall be due
from Tenant during the first twelve (12) months commencing with the Commencement
Date.

     (d)  Manner of Payment.
          -----------------

          (i)    Landlord shall give Tenant notice of Landlord's estimate of
amounts payable under this Section 3.2 for each Adjustment Period based upon
                           -----------
generally accepted accounting principles consistently applied.  By the first day
of each month during the Adjustment Period, Tenant shall pay Landlord one-
twelfth (1/12th) of the estimated amount.  If for any reason the estimate is not
given before the Adjustment Period begins, Tenant shall continue to pay on the
basis of the previous year's estimate, if any, until the month after the new
estimate is given.

          (ii)   Within one hundred twenty (120) days after each Adjustment
Period ends, or as soon thereafter as reasonably practical, Landlord shall give
Tenant a statement (the "Statement"), in reasonable detail as to line items,
                         ---------
showing the: (A) actual Operating Expenses for the Adjustment Period; (B) Base
Operating Expenses; (C) the Expense Increase for the Adjustment Period; (D) the
amount of Tenant's Pro Rata Share of the Expense Increase; (E) the amount, if
any, paid by Tenant during the Adjustment Period towards the Expense Increase;
and (F) the amount Tenant owes towards the Expense Increase or the amount
Landlord owes as a refund. Delay by Landlord in providing to Tenant any
Statement shall not relieve Tenant from the obligation to pay any
<PAGE>

Expense Increase upon the rendering of such Statements nor shall it relieve
Landlord from paying any refund if so due.

          (iii)  If the Statement shows that the actual amount Tenant owes for
the Adjustment Period is less than any estimated Expense Increase paid by Tenant
during the Adjustment Period, Landlord shall return the difference (the
"Overpayment"). If the Statement shows that the actual amount Tenant owes is
 -----------
more than any estimated Expense Increase paid by Tenant during the Adjustment
Period, Tenant shall pay the difference (the "Underpayment").  The Overpayment
                                              ------------
or Underpayment shall be paid within thirty (30) days after the Statement is
delivered to Tenant.

          (iv)   During any Adjustment Period in which this Lease is not in
effect for a complete calendar year, unless it was ended due to Tenant's
default, Tenant's obligation for Additional Rent for those Adjustment Periods
shall be prorated by multiplying the Additional Rent for the Adjustment Period
by a fraction expressed as a percentage, the numerator of which is the number of
days of the Adjustment Period included in the Term and the denominator of which
is 365.

     Section 3.3  Security.  (a)  Tenant has delivered to Landlord, as security
                  --------
for the performance of Tenant's obligations under this Lease, either (i) the sum
of One Million Six Hundred Thousand and No/100 Dollars ($1,600,000.00) by good
check (the "Security Deposit"), (ii) an unconditional, irrevocable letter of
            ----------------
credit in the amount of One Million Six Hundred Thousand and No/100 Dollars
($1,600,000.00) in a form satisfactory to Landlord, issued by a New York
Clearinghouse member bank, including First Union National Bank, or a bank
reasonably satisfactory to Landlord and available for presentation in the
Borough of Manhattan in New York, New York ("Letter of Credit") or (iii) a
                                             ----------------
Security Deposit and a Letter of Credit, the sum of which equals One Million Six
Hundred Thousand and No/100 Dollars ($1,600,000.00; such amount whether in the
form of a Security Deposit or Letter of Credit or both being herein referred to
as the "Initial Amount").  The Letter of Credit shall either (i) expire on the
        --------------
date which is sixty (60) days after the expiration or earlier termination of
this Lease (the "LC Date") or (ii) be automatically self-renewing until the LC
                 -------
Date.  If Landlord, at any time during the Term, is not reasonably satisfied
with the bank issuing the Letter of Credit, it may so notify Tenant, and Tenant,
within ten (10) business days after receipt of such notice, shall replace the
Letter of Credit then held by Landlord with a substitute letter of credit (the
"Substitute Letter of Credit") issued by a New York Clearinghouse member bank
 ---------------------------
(or other bank reasonably acceptable to Landlord) which satisfies the terms of
this Section 3.3(a). If the Letter of Credit or any replacement Letter of Credit
     --------------
has an expiration date or is otherwise scheduled to terminate prior to the LC
Date, then at least thirty (30) days prior to such expiration or termination
date, Tenant shall deliver to Landlord a replacement Letter of Credit issued by
the issuing bank of the then current Letter of Credit, or a bank reasonably
satisfactory to Landlord, available for presentation in the Borough of Manhattan
in New York, New York, in substantially the same form as the original Letter of
Credit, and in the amount provided for herein. If Tenant shall not have provided
such replacement Letter of Credit by the date which is thirty (30) days prior to
the expiration or other scheduled termination of the then current Letter of
Credit, then Landlord shall have the right to draw down the full amount the then
current Letter of Credit, at which time the amount so drawn shall become the
Security Deposit.

     (b)  On the third (3rd) anniversary of the Commencement Date, the Initial
Amount shall be reduced to an amount equal to Nine Hundred Twenty Thousand and
No/100 Dollars ($920,000.00), provided that no default shall then be continuing
                              --------
and any amounts drawn by Landlord upon the Security Deposit or the Letter of
Credit have been replaced by Tenant.  On the fourth (4th) anniversary of the
Commencement Date, the amount of the Security Deposit or Letter of Credit or
both, as applicable, shall then be reduced to an amount equal to Two Hundred
Forty Thousand and No/100 Dollars ($240,000.00), provided that no default shall
                                                 --------
then be continuing and any amounts drawn by Landlord upon the Security Deposit
or the Letter of Credit have been replaced by Tenant.

     (c)  On or before the LC Date:  (i) if there shall be no uncured defaults
hereunder, Landlord shall return to Tenant the Security Deposit or Letter of
Credit or Substitute Letter of Credit then held by Landlord or (ii) if Landlord
shall have drawn upon such Security Deposit or Letter of Credit or Substitute
Letter of Credit to remedy defaults by Tenant in the payment or performance of
any of Tenant's obligations under this Lease, Landlord shall return to Tenant
that
<PAGE>

portion, if any, of such Security Deposit or of the proceeds of the Letter of
Credit or Substitute Letter of Credit remaining in Landlord's possession, which
has not been applied to remedy, and will not be required to remedy, any Tenant
default. If Landlord shall have so drawn upon the Security Deposit or the Letter
of Credit, Tenant shall, upon written demand made prior to the LC Date, deposit
with Landlord, or cause the Letter of Credit to be increased by, a sum equal to
the amount so drawn by Landlord.

     Section 3.4  Tenant's Review Right.  Following Tenant's receipt of the
                  ---------------------
annual Statement for any Lease Year until ninety (90) days thereafter, Tenant
shall have the right to dispute items on such Statement. In such event, Landlord
and Tenant will consult in a good faith effort to resolve the dispute within
thirty (30) days after Landlord receives notice of such dispute. In the event
that such consultations within such thirty (30) day period do not resolve the
matter, Tenant shall be entitled, provided that Tenant shall have paid to
Landlord the amounts shown thereon as due from Tenant, to have an independent
certified public accounting firm hired by Tenant and reasonably approved by
Landlord review the books, receipts and records pertaining to such disputed
items for such Lease Year. Tenant shall have the right to make copies of such
books, receipts and records. The results of any such review shall be provided
simultaneously to Landlord and Tenant by the accounting firm and shall be
binding upon Landlord and Tenant and, in the event that any such review reveals
a net underpayment or overpayment with respect to Operating Expenses and/or the
Expense Increase, the applicable party shall pay to the other, within ten (10)
business days following demand therefor, the amount necessary to effect the
appropriate adjustments. In the event an overpayment exceeds 7%, Landlord shall
pay the costs of the accounting firm's review, not to exceed $2,500.00. No more
than one such review may be conducted with respect to any Lease Year. Tenant
shall keep all information gained in connection with any review or inspection of
Landlord's records, and all information contained in any annual Statement,
confidential and shall not disclose it to third parties except to carry out the
purposes of this Section and except as required by law; provided, however, that
                                                        --------  -------
Tenant may disclose such information to the extent reasonably needed in
connection with financing arrangements or assignments of Tenant's interests in
the Premises so long as Tenant takes reasonable steps to assure that the
applicable lender or proposed assignee keeps such information confidential.

                                  ARTICLE IV.

Section 4.1  Services.
             --------

     (a)     Services Provided. Landlord shall furnish to Tenant while Tenant is
             -----------------
occupying the Premises:

             (i)   Hot and cold domestic water in common use restrooms and
toilets in locations provided for general use and as reasonably deemed by
Landlord to be in keeping with the Project standards.

             (ii)  Heating and air conditioning in season from 8:00 a.m. to 6:00
p.m. on Monday through Friday and 9:00 a.m. to 1:00 p.m. on Saturday ("Business
                                                                       --------
Hours"), excluding the hereinafter defined Holidays, subject to curtailment as
-----
required by governmental laws, rules or regulations, in such amounts as are
considered by Landlord to be standard, but such service at times during weekdays
other than the hours stated above, and on Saturdays, Sundays and Holidays, shall
be furnished only upon request of Tenant, and for such service Tenant shall pay
Landlord upon demand an amount equal to  Landlord's actual costs at that time of
providing such service.

             (iii) Electric lighting service for all public areas and special
service areas of the Building in the manner and to the extent deemed by Landlord
to be standard.

             (iv)  Janitor service on a five (5) day week basis in a manner
considered by Landlord to be standard for similar projects in the area and as
described in Exhibit H attached hereto; provided, however, if Tenant's floor
             ---------                  --------  -------
coverings or other improvements require special care, Tenant shall pay the
additional cleaning cost attributable thereto.

             (v)   Access control for the Project comparable as to coverage,
control and responsiveness (but not necessarily as to means for accomplishing
same) to other similarly
<PAGE>

situated multi-tenant office buildings in the vicinity; provided, however,
                                                        --------  -------
Landlord shall have no responsibility to prevent, and shall not be liable to
Tenant for, any liability or loss to Tenant, its agents, employees and visitors
arising out of losses due to theft, burglary, or damage or injury to persons or
property caused by persons gaining access to the Premises, and Tenant hereby
releases Landlord from all liability for such losses, damage or injury.

             (vi)  Sufficient electrical capacity to operate (i) incandescent
lights, typewriters, calculating machines, photocopying machines and other
machines of similar voltage electrical consumption (120/220 volts), provided
that the total rated electrical design load for said lighting and machines of
low electrical voltage shall not exceed four and one-half (4.50) watts per
square foot of rentable area; and (ii) lighting and equipment of high voltage
electrical consumption (277/480 volts), provided that the total rated electrical
design load for said lighting and equipment of high electrical voltage shall not
exceed two (2.00) watts per square foot of rentable area (each such rated
electrical design load to be hereinafter referred to as the "Building standard
rated electrical design load").  Tenant shall be allocated Tenant's pro rata
share of the Building standard circuits provided on the floor(s) Tenant
occupies.

     Should Tenant's fully connected electrical design load exceed the Building
standard rated electrical design load for either low or high voltage electrical
consumption, or if Tenant's electrical design requires low voltage or high
voltage circuits in excess of Tenant's share of the Building standard circuits,
Landlord will (at Tenant's expense) install one (1) additional high voltage
panel and/or one (1) additional low voltage panel with associated transformer,
space for which has been provided in the base building electrical closets based
on a maximum of two (2) such additional panels per floor for all tenants on the
floor (which additional panels and transformers shall be hereinafter referred to
as the "additional electrical equipment"). If the additional electrical
equipment is installed because Tenant's low or high voltage rated electrical
design load exceeds the applicable Building standard rated electrical design
load, then a meter shall also be added (at Tenant's expense) to measure the
electricity used through the additional electrical equipment.

     The design and installation of any additional electrical equipment (or
related meter) required by Tenant shall be subject to the prior approval of
Landlord (which approval shall not be unreasonably withheld). All expenses
incurred by Landlord in connection with the review and approval of any
additional electrical equipment shall also be reimbursed to Landlord by Tenant.
Tenant shall also pay on demand the actual metered cost of electricity consumed
through the additional electrical equipment (if applicable), plus any actual
accounting expenses incurred by Landlord in connection with the metering
thereof.

     If any of Tenant's electrical equipment requires conditioned air in excess
of Building standard air conditioning, the same shall be installed by Landlord
(on Tenant's behalf), and Tenant shall pay all design, installation, metering
and operating costs relating thereto.

     If Tenant requires that certain areas within the Premises must operate in
excess of the Business Hours set forth above, the electrical service to such
areas shall be separately circuited and metered such that Tenant shall be billed
the actual costs associated with electricity consumed during hours other than
the Business Hours. Without limiting the foregoing, Tenant shall arrange to have
its network and/or telecommunications operating center separately circuited and
metered as aforesaid.

          (vii)  All fluorescent bulb and ballast replacement for Building
standard lighting in all areas and all incandescent bulb replacement in public
areas, toilet and restroom areas and stairwells.

          (viii) Nonexclusive operatorless passenger elevator service to the
Premises twenty-four (24) hours per day; provided, that Landlord may reasonably
limit the number of elevators in operation on weekdays after the Business Hours.

     (b)  Cessation of Services. To the extent the services described in Section
          ---------------------                                          -------
4.1(a) of this Lease require electricity, gas and water supplied by public
------
utilities, Landlord's covenants thereunder shall only impose on Landlord the
obligation to use its reasonable efforts to cause the applicable public
utilities to furnish the same. Failure by Landlord to furnish the services
described in this Section 4.1 to any extent, or any cessation thereof, shall
                  -----------
not, unless such failure
<PAGE>

was caused by the gross negligence or willful misconduct of Landlord or of
Landlord's employees, agents and contractors, (i) render Landlord in default
hereunder or liable in any respect for damages to either person or property, or
(ii) be construed as an eviction of Tenant, or (iii) work an abatement of Rent,
or (iv) relieve Tenant from fulfillment of any covenant or agreement hereof. In
addition to the foregoing, should any of the equipment or machinery break down,
cease to function properly for any cause other than the gross negligence or
willful misconduct of Landlord or Landlord's employees, agents or contractors or
be intentionally turned off for testing or maintenance purposes, Tenant shall
have no claim for abatement or reduction of Rent or damages on account of an
interruption in service occasioned thereby or resulting therefrom; provided,
                                                                   --------
however, Landlord agrees to use diligent efforts to repair said equipment or
-------
machinery and to restore said services and Tenant's rent shall abate after five
(5) consecutive business days of such cessation of services for the duration of
the cessation so long as the Premises are not and cannot reasonably be used for
the conduct of Tenant's business operation and are not being so used by Tenant.

     (c)  Holidays.  The following dates shall collectively be known as
          --------
"Holidays" and individually known as a "Holiday":  New Year's Day; Memorial Day;
 --------                               -------
Independence Day; Labor Day; Thanksgiving Day; Friday following Thanksgiving
Day; Christmas Day; any other holiday recognized and taken by tenants occupying
at least one-half (1/2) of the rentable area of office space of the Building and
any other holiday recognized and taken by any unions which service the Building
in any manner.  If in the case of any Holiday, a different day shall be observed
than the respective day above described, then that day which constitutes the day
observed by national banks in the city or proximate area in which the Building
is located, on account of such Holiday, shall constitute the Holiday under this
Lease.

     Section 4.2   Keys and Locks.  Subject to the terms and provisions of this
                   --------------
Lease, Tenant shall have access to the Premises 24 hours a day, 7 days a week.
Landlord shall initially furnish Tenant with [five hundred thirty-one (531)]
card keys or keys, respectively, for the building entrance and for the standard
corridor doors serving the Premises.  Additional keys will be furnished by
Landlord upon an order signed by Tenant and at Tenant's expense.  All such keys
shall remain the property of Landlord.  Without the prior written consent of
Landlord, no additional locks shall be allowed on any door of the Premises, and
Tenant shall not make or permit to be made any duplicate keys, except those
furnished by Landlord.  Upon termination or expiration of this Lease or a
termination of possession of the Premises by Tenant, Tenant shall surrender to
Landlord all keys to any locks on doors entering or within the Premises.
Landlord shall also provide card-key controlled access (or other similar access
control device or mechanism as Landlord may from time to time elect to provide)
intended to limit the general public's access to the Building during other than
Business Hours.  Landlord, however, shall have no liability to Tenant, its
employees, agents, invitees or licensees for any loss, damage or injury of any
kind or nature caused by or as a result of the presence of any unauthorized
person in the Premises, the Building or the Project, including without
limitation any loss, damage or injury due to theft, burglary or other criminal
conduct by any person, nor shall Landlord be required to insure against any such
loss, damage or injury

     Section 4.3   Graphics and Building Directory.  Landlord shall provide and
                   -------------------------------
install, at Tenant's expense, all letters or numerals at the entrance to the
Premises, and a strip containing a listing of Tenant's name on the Building
directory board to be placed in the main lobby of the Building.  All such
letters and numerals shall be in Building standard graphics.  Landlord shall not
be liable for any inconvenience or damage occurring as a result of any error or
omission in any directory or graphics.  No signs, numerals, letters or other
graphics shall be used or installed by Tenant on the exterior of, or which may
be visible from outside, the Premises, unless approved in writing by Landlord.
Additionally, Landlord agrees to provide to Tenant, at Tenant's sole cost and
expense, prominent and exclusive signage (subject however to the provisions of
Section 5.2) at or about the top of the Building to the maximum size permitted
under the signage provisions of the Fairfax County Zoning Ordinance and any
other applicable laws or covenants.  The design, size, placement, style,
lighting, colors and materials of such sign shall require Landlord's prior
approval, which approval will not be unreasonably withheld, conditioned or
delayed, and will be subject further to Tenant's obtaining approval from the
Dulles Tech Center association and applicable governmental authorities.  Upon
the expiration or earlier termination of this Lease, Tenant shall remove all
such signage and/or graphics and repair any and all damage caused by or
resulting from the installation, maintenance, operation and/or removal of such
signage or graphics at Tenant's sole cost and expense.  Tenant's proposed
signage is attached
<PAGE>

hereto as Exhibit G, and Landlord approves such signage, subject to Tenant's
obtaining the other approvals and permits referred to hereinabove.

                                  ARTICLE V.

     Section 5.1   Occupancy of Premises.  Tenant shall throughout the Term of
                   ---------------------
this Lease, at its own expense, maintain the Premises and all improvements
thereon and keep them free from waste, damage or nuisance, and shall deliver up
the Premises in a clean and sanitary condition at the expiration or termination
of this Lease or the termination of Tenant's right to occupy the Premises by
Tenant, in good repair and condition, reasonable wear and tear excepted.  In the
event Tenant should neglect to maintain and/or return the Premises in such
manner at any time, Landlord shall have the right, but not the obligation, to
cause repairs or corrections to be made, and any reasonable costs therefor shall
be payable by Tenant to Landlord within ten (10) days of demand therefor by
Landlord.  Upon the expiration or termination of this Lease or the termination
of Tenant's right to occupy the Premises by Tenant, Landlord shall have the
right to reenter and resume possession of the Premises.  No act or thing done by
Landlord or any of Landlord's agents (hereinafter defined) during the Term of
the Lease shall be deemed an acceptance of a surrender of the Premises, and no
agreement to accept a surrender of the Premises shall be valid unless the same
be made in writing and executed by Landlord.  Tenant shall notify Landlord at
least ten (10) days prior to vacating the Premises and shall arrange to meet
with Landlord for a joint inspection of the Premises.  If Tenant fails to give
such notice or to arrange for such inspection, then Landlord's inspection of the
Premises shall be deemed correct for the purpose of determining Tenant's
responsibility for repair and restoration of the Premises.

     Section 5.2   Entry for Repairs and Inspection.  Tenant shall permit
                   --------------------------------
Landlord and its agents to enter the Premises (provided Landlord gives Tenant
reasonable prior notice and Tenant has the option to have a representative
accompanying Landlord during such entry) at all reasonable times to inspect the
same; to show the Premises to prospective tenants (within twelve (12) months of
the expiration of the term of this Lease), or interested parties such as
prospective lenders and purchasers; to exercise its rights under this Lease; to
clean, repair, alter or improve the Premises or the Building; to discharge
Tenant's obligations when Tenant has failed to do so within the time required
under this Lease or within a reasonable time after written notice from Landlord,
whichever is earlier; to post notices of nonresponsibility and similar notices
and "For Sale" signs at any time and to place "For Lease" signs upon or adjacent
to the Building or the Premises at any time within twelve (12) months of the
expiration of the term of this Lease.  Tenant shall permit Landlord and its
agents to enter the Premises at any time in the event of an emergency.  When
reasonably necessary, Landlord may temporarily close entrances, doors,
corridors, elevators or other facilities without liability to Tenant by reason
of such closure.

     Section 5.3   Hazardous Materials.
                   -------------------

     (a)  As used in this Lease, the term "Hazardous Materials" shall mean and
                                           -------------------
include any substance that is or contains petroleum, asbestos, polychlorinated
biphenyls, lead, or any other substance, material or waste which is now or is
hereafter classified or considered to be hazardous or toxic under any federal,
state or local law, rule, regulation or ordinance relating to pollution or the
protection or regulation of human health, natural resources or the environment
(collectively "Environmental Laws") or poses or threatens to pose a hazard to
               ------------------
the health or safety of persons on the Premises or any adjacent property.
Landlord represents and warrants that to the best of Landlord's actual
knowledge, there are no Hazardous Materials located in, on or under the Building
or the Land, and Landlord has received no notices concerning violation of any
laws relating to Hazardous Materials with respect to the Building or the Land.
If Hazardous Materials are discovered in the Building or on the Land after the
Commencement Date and were not caused or permitted by Tenant or Tenant's
employees, assignees agents or invitees, then Landlord will be responsible for
all costs and expenses associated with regulatory requirements to eliminate any
violations of law resulting from such presence and Landlord shall indemnify,
defend, and hold Tenant and Tenant's employees, assignees, agents and invitees
harmless from any and all claims, costs, liabilities or expenses associated with
such Hazardous Materials.

     (b)  Tenant agrees that during its use and occupancy of the Premises it
will not permit Hazardous Materials to be present on or about the Premises
except in a manner and quantity necessary for the ordinary performance of
Tenant's business and that it will comply with all Environmental Laws relating
to the use, storage or disposal of any such Hazardous Materials.
<PAGE>

     (c)  If Tenant's use of Hazardous Materials on or about the Premises
results in a release, discharge or disposal of Hazardous Materials on, in, at,
under, or emanating from, the Premises or the property in which the Premises are
located, Tenant agrees to investigate, clean up, remove or remediate such
Hazardous Materials in full compliance with (a) the requirements of (i) all
Environmental Laws and (ii) any governmental agency or authority responsible for
the enforcement of any Environmental Laws; and (b) any additional requirements
of Landlord that are reasonably necessary to protect the value of the Premises
or the property in which the Premises are located. Landlord shall also have the
right, but not the obligation, to take whatever action with respect to any such
Hazardous Materials that it deems reasonably necessary to protect the value of
the Premises or the property in which the Premises are located. All costs and
expenses paid or incurred by Landlord in the exercise of the right set forth in
this Section 5.3(c) shall be payable by Tenant upon demand.
     --------------

     (d)  Upon reasonable notice to Tenant, Landlord may, at its sole cost and
expense unless a violation is discovered, inspect the Premises for the purpose
of determining whether there exists on the Premises any Hazardous Materials or
other condition or activity that is in violation of the requirements of this
Lease or of any Environmental Laws.  The right granted to Landlord herein to
perform inspections shall not create a duty on Landlord's part to inspect the
Premises, or liability on the part of Landlord for Tenant's use, storage or
disposal of Hazardous Materials, it being understood that Tenant shall be solely
responsible for all liability in connection therewith.

     (e)  Tenant shall surrender the Premises to Landlord upon the expiration or
earlier termination of this Lease free of debris, waste or Hazardous Materials
placed on or about the Premises by Tenant or its agents, employees, contractors
or invitees, and in a condition which complies with all Environmental Laws.

     (f)  Tenant agrees to indemnify and hold harmless Landlord and Landlord's
employees, assignees, agents and invitees from and against any and all claims,
losses (including, without limitation, loss in value of the Premises or the
property in which the Premises are located), liabilities and expenses (including
reasonable attorney's fees) sustained by Landlord attributable to (i) any
Hazardous Materials placed on or about the Premises by Tenant or its agents,
employees, contractors or invitees or (ii) Tenant's breach of any provision of
this Section 5.3.
     -----------

     (g)  The provisions of this Section 5.3 shall survive the expiration or
                                 -----------
earlier termination of this Lease.

                                  ARTICLE VI.

     Section 6.1   Leasehold Improvements.
                   ----------------------

     (a)  Acceptance of Premises.  Tenant has made a complete inspection of the
          ----------------------
Premises and, except as set forth in this Section 6.1 and Exhibit E, shall
                                          -----------     ---------
accept the Premises and the Project in their "AS IS," "WHERE IS," and "WITH ALL
FAULTS" condition on the Commencement Date without recourse to Landlord, subject
to the terms of Exhibit E attached hereto and hereby made a part hereof.  Except
                ---------
as expressly provided in this Lease, Landlord shall have no obligation to
furnish, equip or improve the Premises or the Project.  The taking of possession
of the Premises by Tenant shall be, except as set forth in this Section 6.1 and
                                                                -----------
Exhibit E, conclusive evidence against Tenant that (i) Tenant accepts the
---------
Premises and the Project as being suitable for its intended purpose and in a
good and satisfactory condition, (ii) acknowledges that the Premises and the
Project comply fully with Landlord's covenants and obligations under this Lease
and (iii) waives any defects in the Premises and its appurtenances and in all
other parts of the Project.  Notwithstanding the foregoing,  Landlord agrees
that upon the Commencement Date, the Building, its common areas, and all central
mechanical, electrical and plumbing systems will be in good working order,
condition and repair, and the Building and the Land will be in compliance with
all applicable laws in effect at the Commencement Date (subject to Tenant's
performance of the Tenant Work).  In the event of a material breach of the
covenant contained in the preceding sentence, Landlord shall promptly after
receipt of written notice from Tenant setting forth the nature and extent of
such material breach, rectify same at Landlord's cost and expense, as Tenant's
sole remedy therefor.  After the Commencement Date,
<PAGE>

Landlord will be responsible for the costs of compliance with applicable laws
with respect to the common areas of the Building and the Land as well as all
structural elements of the Building, provided that such costs are not the result
of Tenant's use, occupancy, manner of use or occupancy, or the negligence of
Tenant.

     (b)  Improvements and Alterations.  Tenant shall not make or allow to be
          ----------------------------
made (except as otherwise provided in this Lease) any improvements, alterations
or physical additions (including fixtures) in or to the Premises or the Project,
without first obtaining the written consent of Landlord, which approval shall
not be unreasonably withheld, conditioned or delayed (except in the case of
structural changes or changes to any Building system, in which case Landlord may
withhold such approval in its sole discretion), including Landlord's written
approval of Tenant's contractor(s) and of the plans, working drawings and
specifications relating thereto (none of which shall be unreasonably withheld,
conditioned or delayed, except in the case of structural changes or changes to
any Building system, in which case Landlord may withhold such approval in its
sole discretion).  Approval by Landlord of any of Tenant's drawings and plans
and specifications prepared in connection with any alterations, improvements,
modifications or additions to the Premises or the Project shall not constitute a
representation or warranty of Landlord as to the adequacy or sufficiency of such
drawings, plans and specifications, or alterations, improvements, modifications
or additions to which they relate, for any use, purpose or conditions, but such
approval shall merely be the consent of Landlord as required hereunder.  Except
as otherwise expressly provided in Exhibit E attached hereto, any and all
furnishing, equipping and improving of or other alteration and addition to the
Premises shall be: (i) made at Tenant's sole cost, risk and expense, and Tenant
shall pay for Landlord's reasonable costs incurred in connection with and as a
result of such alterations or additions; (ii) performed in a good and
workmanlike manner with labor and materials of such quality as Landlord may
reasonably require; (iii) constructed in accordance with all plans and
specifications approved in writing by Landlord prior to the commencement of any
such work; (iv) prosecuted diligently and continuously to completion so as to
minimize interference with the normal business operations of other tenants in
the Building, the performance of Landlord's obligations under this Lease or any
mortgage or ground lease covering or affecting all or any part of the Building
or the Land and any work being done by contractors engaged by Landlord with
respect to or in connection with the Building; and (v) performed by contractors
approved in writing by Landlord, which approval shall not be unreasonably
withheld, conditioned or delayed.  Tenant shall have no (and hereby waives all)
rights to payment or compensation for any such item.  Tenant shall notify
Landlord upon completion of such alterations, improvements, modifications or
additions and Landlord shall inspect same for workmanship and compliance with
the approved plans and specifications.  Tenant and its contractors shall comply
with all commercially reasonable requirements Landlord may impose on Tenant or
its contractors with respect to such work (including but not limited to,
insurance and indemnity requirements), and shall deliver to Landlord a complete
copy of the "as-built" or final plans and specifications for all alterations or
physical additions so made in or to the Premises within thirty (30) days of
completing the work.  Tenant shall not place safes, vaults, filing cabinets or
systems, libraries or other heavy furniture or equipment within the Premises
without Landlord's prior written consent, which approval shall not be
unreasonably withheld, conditioned or delayed.

          Notwithstanding the foregoing provisions of this Section 6.1(b),
                                                           --------------
Tenant shall notify Landlord of, but shall not be obligated to obtain Landlord's
prior consent for any improvement, alteration or physical addition which costs
less than $20,000.00 and does not affect the Building's structure or the
Building's HVAC, electrical or plumbing systems.

     (c)  Title to Alterations.  All alterations, physical additions,
          --------------------
modifications or improvements in or to the Premises (including fixtures) shall,
when made, become the property of Landlord and shall be surrendered to Landlord
upon termination or expiration of this Lease or termination of Tenant's right to
occupy the Premises, whether by lapse of time or otherwise, without any payment,
reimbursement or compensation therefor; provided, however, that (i) Tenant shall
                                        --------  -------
retain title to and shall remove from the Premises movable equipment or
furniture owned by Tenant, (ii) Tenant repairs any damage caused by a removal
pursuant to Section 6.1(c)(i), and (iii) Tenant returns the Premises to their
            -----------------
condition existing immediately prior to removal  (with respect to a removal of
an improvement pursuant to Section 6.1(c)(i) only).  Notwithstanding any of the
                           -----------------
foregoing to the contrary, Landlord may require Tenant to remove all
alterations, additions or improvements to the Premises (including, but not
limited to, the network and/or telecommunications operations center) that are
other than a standard office buildout in the
<PAGE>

Reston/Herndon area in which the Building is located, including, without
limitation, any cabling or other computer, satellite or telecommunications
equipment or hardware, whether or not such alterations, additions, or
improvements are located in the Premises upon the expiration or earlier
termination of this Lease or the termination of Tenant's right to possession of
the Premises and restore the same to Building standard condition, reasonable
wear and tear excepted. If Tenant fails to remove any movable equipment or
furniture or any alterations, additions or improvements so required hereunder to
be removed, then Landlord may remove such items, at Tenant's sole cost and
expense. The rights conferred to Landlord under this Section 6.1(c) shall be in
                                                     --------------
addition to (and not in conflict with) any other rights conferred on Landlord by
this Lease, in equity or at law. Notwithstanding the foregoing provisions of
this Section 6.1(c), Tenant shall not be required to remove any addition,
     --------------
modification or improvement to the Premises unless Landlord informs Tenant in
writing, either at the time Landlord gives its consent to such addition,
modification or improvement or within ten (10) business days of Tenant's written
request for an addition, modification or improvement which does not require
Landlord's consent, that it will have to remove such addition, modification or
improvement at the expiration or earlier termination of this Lease.

     (d)  Personal Property Taxes; Sales, Use and Excise Taxes.  Tenant shall be
          ----------------------------------------------------
responsible for and shall pay ad valorem taxes and other taxes, assessments or
charges levied upon or applicable to Tenant's personal property, the value of
Tenant's leasehold improvements in the Premises in excess of Building standard
(and if the taxing authorities do not separately assess Tenant's leasehold
improvements, Landlord may make a reasonable allocation of the taxes assessed on
the Project to give effect to this Section 6.l(d)) and all license fees and
                                   --------------
other fees or charges imposed on the business conducted by Tenant on the
Premises before such taxes, assessments, charges or fees become delinquent.
Tenant shall also pay to Landlord with all Rent due and owing under this Lease
an amount equal to any sales, rental, excise and use taxes levied, imposed or
assessed by the State or any political subdivision thereof or other taxing
authority upon any amounts classified as Rent.

     Section 6.2   Repairs by Landlord.  All repairs, alterations or additions
                   -------------------
that affect the Project's structural components  shall be made by Landlord or
its contractors only, and, in the case of any damage to such components or
systems caused the negligence or willful misconduct of Tenant or Tenant's
agents, shall be paid for by Tenant in an amount equal to Landlord's costs plus
twelve percent (12%) as an overhead expense.  Unless otherwise provided herein,
Landlord shall not be required to make any improvements to or repairs of any
kind or character to the leasehold improvements located in the Premises during
the Term, except such repairs as Landlord deems necessary for normal maintenance
operations of the Building.

     Section 6.3   Repairs by Tenant.  Subject to Section 6.2 of this Lease,
                   -----------------              -----------
Tenant shall be responsible, at its own cost and expense, for all repair or
replacement of any damage to the leasehold improvements in the Premises (unless
such damage is caused by the negligence or willful misconduct of Landlord or
Landlord's employees, agents or contractors), together with any damage to the
Project or any part thereof caused by Tenant or any of Tenant's agents.  Except
insofar as Landlord is expressly obligated under this Lease to maintain and
repair the Building, in addition to the maintenance and repair obligations of
Tenant otherwise expressly set forth in this Lease, Tenant is also obligated to
perform, at Tenant's own cost and expense and risk, all other maintenance and
repairs necessary or appropriate to cause the Premises to be maintained in good
condition and suitable for Tenant's intended commercial purpose reasonable wear
and tear excepted.

     Section 6.4   Liens.  Tenant shall keep the Premises and the Building free
                   -----
from any liens, including but not limited to liens filed against the Premises by
any governmental agency, authority or organization, arising out of any work
performed, materials ordered or obligations incurred by or on behalf of Tenant,
and Tenant hereby agrees to indemnify and hold Landlord, its agents, employees,
independent contractors, officers, directors, partners, and shareholders
harmless from any liability, cost or expense associated  with any lien caused by
Tenant.  Tenant shall cause any lien imposed as a result of Tenant's actions or
inaction to be released of record by payment or posting of the proper bond
acceptable to Landlord within ten (10) days after the earlier of imposition of
the lien or written request by Landlord.  Tenant shall give Landlord written
notice of Tenant's intention to perform work on the Premises which might result
in any claim of lien, at least ten (10) days prior to the commencement of such
work to enable Landlord to post and record a notice of nonresponsibility or
other notice deemed proper before
<PAGE>

commencement of any such work. If Tenant fails to remove any lien within the
prescribed ten (10) day period, then Landlord may do so at Tenant's expense and
Tenant's reimbursement to Landlord for such amount, including reasonable
attorneys' fees and costs, shall be deemed Additional Rent. Tenant shall have no
power to do any act or make any contract which may create or be the foundation
for any lien, mortgage or other encumbrance upon the reversion or other estate
of Landlord, or of any interest of Landlord in the Premises.

     Section 6.5   Indemnification.  Tenant shall defend, indemnify and hold
                   ---------------
harmless Landlord, its agents, employees, officers, directors, partners and
shareholders ("Landlord's Related Parties") from and against any and all
               --------------------------
liabilities, judgments, demands, causes of action, claims, losses, damages,
costs and expenses, including reasonable attorneys' fees and costs, arising out
of the use, occupancy, conduct, operation, or management of the Premises by, or
the willful misconduct or negligence of, Tenant, its officers, contractors,
licensees, agents, servants, employees, guests, invitees, or visitors in or
about the Building or Premises or arising from any breach or default under this
Lease by Tenant, or arising from any accident, injury, or damage, howsoever and
by whomsoever caused, to any person or property, occurring in or about the
Building or Premises.  This indemnification shall survive termination or
expiration of this Lease.  This provision shall not be construed to make Tenant
responsible for loss, damage, liability or expense resulting from injuries to
third parties caused by the  negligence or willful misconduct of Landlord, or
its officers, contractors, licensees, agents, employees, or invitees.

     Landlord shall indemnify, defend and hold harmless Tenant as well as
Tenant's employees, agents and invitees ("Tenant's Related Parties") from and
                                          ------------------------
against all liability, claims, losses and expenses (i) resulting from the
negligent acts, omissions or willful misconduct of Landlord or Landlord's
Related Parties in connection with Landlord's or Landlord's Related Parties'
activities in, on or about the Project except to the extent that such liability
or claim is for damage to Tenant's personal property, fixtures or furniture in
the Premises and is covered by insurance that Tenant is required to obtain under
this Lease (or would have been covered had Tenant carried the insurance required
under this Lease) and (ii) Landlord's breach of this Lease.  This provision
shall not be construed to make Landlord responsible for any losses, liabilities,
damages or expenses resulting from injuries or damage caused by the negligence
or willful misconduct of Tenant, or its officers, contractors, licensees,
agents, employees or invitees.

                                 ARTICLE VII.

     Section 7.1   Condemnation.
                   ------------

     (a)  Total Taking.  In the event of a taking or damage related to the
          ------------
exercise of the power of eminent domain, by any agency, authority, public
utility, person, corporation or entity empowered to condemn property (including
without limitation a voluntary conveyance by Landlord in lieu of such taking or
condemnation) (individually, a "Taking") of (i) the entire Premises, (ii) so
                                ------
much of the Premises as to prevent or substantially impair its use by Tenant
during the Term of this Lease or (iii) portions of the Building or Project
required for reasonable access to, or reasonable use of, the Premises including,
without limitation, material portions of the parking areas (individually, a
"Total Taking"), the rights of Tenant under this Lease and the leasehold estate
 ------------
of Tenant in and to the Premises shall cease and terminate as of the date upon
which title to the property taken passes to and vests in the condemnor or the
effective date of any order for possession if issued prior to the date title
vests in the condemnor ("Date of Taking").
                         --------------

     (b)  Partial Taking.  In the event of a Taking of only a part of the
          --------------
Premises or of a part of the Project which does not constitute a Total Taking
during the Term of this Lease (individually, a "Partial Taking"), the rights of
                                                --------------
Tenant under this Lease and the leasehold estate of Tenant in and to the portion
of the property taken shall cease and terminate as of the Date of Taking, and an
adjustment to the Rent shall be made based upon the reduced area of the
Premises.

     (c)  Termination by Landlord.  In the event of a Taking of the Building
          -----------------------
(other than the Premises) such that, in Landlord's reasonable opinion, the
Building cannot be restored in a manner that makes its continued operation
practically or economically feasible, Landlord may terminate this Lease by
giving notice to Tenant within ninety (90) days after the date notice of such
Taking is received by Landlord.
<PAGE>

     (d)  Rent Adjustment.  If this Lease is terminated pursuant to this Section
          ---------------                                                -------
7.1, Landlord shall refund to Tenant any prepaid unaccrued Rent and any other
---
sums due and owing to Tenant (less any sums then due and owing Landlord by
Tenant), and Tenant shall pay to Landlord any remaining sums due and owing
Landlord under this Lease, each prorated as of the Date of Taking where
applicable.

     (e)  Repair.  If this Lease is not terminated as provided for in this
          ------
Section 7.1, then Landlord at its expense shall promptly repair and restore the
-----------
Building, Project and/or the Premises to approximately the same condition that
existed at the time Tenant entered into possession of the Premises, wear and
tear excepted (and Landlord shall have no obligation to repair or restore
Tenant's improvements to the Premises or Tenant's Property), except for the part
taken, so as to render the Building or Project as complete an architectural unit
as practical, but only to the extent of the condemnation award received by
Landlord for the damage.

     (f)  Awards and Damages.  Except as expressly provided below, Landlord
          ------------------
reserves all rights to damages and awards paid because of any Partial or Total
Taking of the Premises or the Project.  So long as it does not reduce the amount
of the award payable to Landlord, Tenant (i) shall be entitled to receive any
amount attributable to any excess of the market value of the Premises for the
remainder of the Term over the present value as of the Expiration Date of the
rent payable for the remainder of the Term and (ii) shall have the right to make
a separate claim in any condemnation proceeding for the taking of the
unamortized or undepreciated value of the improvements and alterations owned by
Tenant which Tenant may remove at the expiration or earlier termination of this
Lease, reasonable removal and relocation costs for any improvements Tenant has
the right to remove and elects to remove, relocation costs, the claim for which
Tenant may pursue by separate action independent of this Lease and any other
amount.  Tenant shall have the right to negotiate directly with the condemnor
for the recovery of the portion of the award that Tenant is entitled to under
subsection (ii) above.  Further, Tenant shall not make claims against Landlord
or the condemning authority for damages.  If a temporary taking of part of the
Premises or a portion of the Project which prevents Tenant's use or occupancy of
all or a material portion of the Premises occurs through (a) the exercise of any
government power (by legal proceedings or otherwise) by condemnor or (b) a
voluntary sale or transfer by Landlord to any condemnor, either under threat of
exercise of eminent domain by a condemnor or while legal proceedings for
condemnation are pending, Rent shall abate during the time of such taking in
proportion to the portion of the Premises taken.  The entire award relating to
the temporary taking shall be and remain the property of Landlord.  Tenant
irrevocably assigns and transfers to Landlord all rights to and interest in such
award and fully releases and relinquishes any claim to, right to make a claim
on, and any other interest in the award.

     Section 7.2   Force Majeure.  Neither Landlord nor Tenant shall be required
                   -------------
to perform any term, provision, agreement, condition or covenant in this Lease
(other than the obligations of Tenant to pay Rent as provided herein) so long as
such performance is delayed or prevented by "Force Majeure", which shall mean
                                             -------------
acts of God, strikes, injunctions, lockouts, material or labor restrictions by
any governmental authority, civil riots, floods, fire, theft, public enemy,
insurrection, war, court order, requisition or order of governmental body or
authority, and any other cause not reasonably within the control of Landlord or
Tenant and which by the exercise of due diligence Landlord or Tenant is unable,
wholly or in part, to prevent or overcome.  Neither Landlord nor any mortgagee
shall be liable or responsible to Tenant for any loss or damage to any property
or person occasioned by any Force Majeure, or for any damage or inconvenience
which may arise through repair or alteration of any part of the Project as a
result of any Force Majeure.

     Section 7.3   Fire or Other Casualty Damage.
                   -----------------------------

     (a)  Damage.  If any portion of the Premises shall be destroyed or damaged
          ------
by fire or any other casualty, Tenant shall immediately give notice thereof to
Landlord.   Within thirty (30) days of the date of Tenant's notice, Landlord
shall provide Tenant with a reasonable written estimate, calculated in good
faith, of the number of days that it will take to restore the Building and/or
Premises (the "Restoration Estimate").  If the Restoration Estimate is greater
               --------------------
than 180 days, both Landlord and Tenant shall have the right to terminate this
Lease by giving 30 days written notice to the other.  If the Restoration
Estimate is less than 180 days, Landlord shall promptly commence and diligently
pursue through completion the restoration of the Building
<PAGE>

and/or Premises and this Lease shall continue in full force and effect. If,
however, the cost of the restoration exceeds the insurance proceeds Landlord
reasonably expects to receive due to the casualty (provided, however, that the
                                                   --------  -------
insurance required to be carried by Landlord by this Lease was in effect on the
date of the casualty) or Landlord's lender demands that such insurance proceeds
be paid to it, Landlord may terminate the Lease, subject to Tenant's right to
propose keeping the Lease in effect by Tenant's paying for the restoration. If
Tenant elects to do so, Tenant shall notify Landlord within ten (10) business
days of receiving Landlord's notice of termination of the Lease, and the parties
shall engage in good faith negotiations to determine the terms of Tenant's
election to pay for the restoration; provided, however, that if the parties do
                                     --------  -------
not reach agreement to keep this Lease in effect within ten (10) business days
after Tenant delivers such written notice to Landlord, then this Lease shall
terminate as of the date set forth in Landlord's notice of termination.
Following a casualty, Tenant's obligation to pay Rent shall be abated in
proportion to the interference caused to its use and occupation of the Premises
provided that Tenant no longer occupies or uses such affected Premises for the
active conduct of its business.

     Notwithstanding the terms of the foregoing paragraph, if the casualty
occurs in the last year of the Term (unless Tenant shall have renewed this Lease
as provided herein) and materially affects Tenant's use or occupation of the
Premises (i.e., more than 25% of the Premises has been damaged, or the cost to
repair is reasonably estimated by Landlord to exceed $250,000), either Landlord
or Tenant may elect to terminate this Lease by giving the other party 30 days
prior written notice.  Notwithstanding the provisions of the immediately
preceding paragraph to the contrary, if Landlord elects to terminate this Lease
as a result of such casualty occurring in the last year of the Term (unless
Tenant shall have renewed this Lease as provided herein), Tenant shall not have
the right to keep this Lease in effect by paying for the restoration.

     (b)  Repair.  Landlord shall use reasonable efforts to give Tenant written
          ------
notice of its decisions, estimates or elections under this Section 7.3 within
                                                           -----------
thirty (30) days after any such damage or destruction.  If Landlord is obligated
to repair and restore the Premises or other portion of the Project, this Lease
shall continue in full force and effect, and the repairs will be made as
promptly as is commercially reasonable (not to exceed 120 days from the date of
the Restoration Estimate, subject to the provisions of Section 7.2 of this
                                                       -----------
Lease.  Should the repairs, despite Landlord's use of commercially reasonable
efforts, not be completed within that period, both Landlord and Tenant shall
each have the option of terminating this Lease by written letter of termination.
If this Lease is terminated as herein permitted, Landlord shall refund to Tenant
any prepaid Rent (unaccrued as of the date of damage or destruction) and any
other sums due and owing by Landlord to Tenant (less any sums then due and owing
Landlord by Tenant) and any remaining sums due and owing by Tenant to Landlord
shall be paid to Landlord.  If Landlord has elected to repair and reconstruct
the Premises or other portion of the Project to the extent stated above, the
Term will be extended for a time equal to the period from the occurrence of such
damage to the completion of such repair and reconstruction.  If Landlord elects
to rebuild the Premises or other portion of the Project, Landlord shall only be
obligated to restore or rebuild the Premises or other portion of the Project to
approximately the same condition as existed at the time Tenant entered into
possession of the Premises, wear and tear excepted and not be required to
rebuild, repair or replace any part of Tenant's Property or Tenant's leasehold
improvements.  Notwithstanding anything contained in this Lease to the contrary,
if Landlord shall elect to repair and restore the Premises or other portion of
the Project pursuant to this Section 7.3, in no event shall Landlord be required
                             -----------
to expend under this Article VII any amount in excess of the proceeds actually
                     -----------
received from the insurance carried by Landlord pursuant to Section 7.4(a) of
                                                            --------------
this Lease.  Landlord shall not be liable for any inconvenience or annoyance to
Tenant or injury to the business of Tenant resulting in any way from such damage
or destruction or the disregard of the repair thereof.

     (c)  Negligence of Tenant.  Notwithstanding the provisions of Sections
          --------------------                                     --------
7.3(a) and 7.3(b) of this Lease, if the Premises, the Project or any portion
-----------------
thereof, are damaged by fire or other casualty resulting from the fault or
negligence of Tenant or any of Tenant's agents, the Rent under this Lease will
not be abated during the repair of that damage, and Tenant will be liable to
Landlord for the cost and expense of the repair and restoration of the Premises,
the Project or any part thereof, caused thereby to the extent that cost and
expense is not covered by insurance proceeds (including without limitation the
amount of any insurance deductible).

     Section 7.4   Insurance.
                   ---------
<PAGE>

     (a)  Landlord shall maintain, or cause to be maintained, standard fire and
extended coverage insurance on the Buildings and Building standard tenant
improvements (excluding leasehold improvements by Tenant in excess of Building
standard and Tenant's Property) in amounts considered by Landlord to be
reasonable and customary.  The insurance required to be obtained by Landlord may
be obtained by Landlord through blanket or master policies insuring other
entities or properties owned or controlled by Landlord.

     (b)  Tenant shall, at its sole cost and expense, procure and maintain
during the Term of this Lease (and during any period prior to the Commencement
Date in which Tenant is performing work in any portion of the Building) all such
policies of insurance as Landlord may require, including without limitation
commercial general liability insurance (including personal injury liability,
premises/operation, property damage, independent contractors) in amounts of not
less than a combined single limit of $5,000,000; comprehensive automobile
liability insurance; business interruption insurance for a period of at least
twelve (12) months; contractual liability insurance; property insurance with
respect to Tenant's Property, and all leasehold improvements, alterations and
additions in excess of Building standard, to be written on an "all risk" basis
for full replacement cost; worker's compensation and employer's liability
insurance; and comprehensive catastrophe liability insurance; all maintained
with companies, on forms and in such amounts as Landlord may, from time to time,
reasonably require and endorsed to include Landlord as an additional insured (on
all but the workers compensation coverage), with the premiums fully paid on or
before the due dates. The insurer must be licensed to do business in the state
in which the Building is located. Tenant, and not Landlord, will be liable for
any costs or damages in excess of the statutory limit for which Tenant would, in
the absence of worker's compensation, be liable. In the event that Tenant fails
to take out or maintain any policy required by this Section 7.4 to be maintained
                                                    -----------
by Tenant, such failure shall be a defense to any claim asserted by Tenant
against Landlord by reason of any loss sustained by Tenant that would have been
covered by such policy, notwithstanding that such loss may have been proximately
caused solely or partially by the negligence or willful misconduct of Landlord
or any of Landlord's Related Parties. If Tenant does not procure insurance as
required, Landlord may, upon advance written notice to Tenant, cause this
insurance to be issued and Tenant shall pay to Landlord the premium for such
insurance within ten (10) days of Landlord's demand, plus interest at the past
due rate provided for in Section 3.1(c) of this Lease until repaid by Tenant.
                         --------------
All policies of insurance required to be maintained by Tenant shall specifically
provide that Landlord shall be given at least thirty (30) days' prior written
notice of any cancellation or nonrenewal of any such policy. A certificate
evidencing each such policy shall be deposited with Landlord by Tenant on or
before the Commencement Date, and a replacement certificate evidencing each
subsequent policy shall be deposited with Landlord at least thirty (30) days
prior to the expiration of the preceding such policy. All insurance policies
obtained by Tenant shall be written as primary policies (primary over any
insurance carried by Landlord), not contributing with and not in excess of
coverage which Landlord may carry, if any.

     Section 7.5   Waiver of Subrogation Rights.  Each party hereto waives all
                   ----------------------------
rights of recovery, claims, actions or causes of actions arising in any manner
in its (the "Injured Party's") favor and against the other party for loss or
damage to the Injured Party's property located within or constituting a part or
all of the Project, to the extent the loss or damage: (a) is covered by the
Injured Party's insurance; or (b) would have been covered by the insurance the
Injured Party is required to carry under this Lease, whichever is greater,
regardless of the cause or origin, including the sole, contributory, partial,
joint, comparative or concurrent negligence of the other party.  This waiver
also applies to each party's directors, officers, employees, shareholders,
partners, representatives and agents.  All insurance carried by either Landlord
or Tenant covering the losses and damages described in this Section 7.5 shall
provide for such waiver of rights of subrogation by the Injured Party's
insurance carrier to the maximum extent that the same is permitted under the
laws and regulations governing the writing of insurance within the state in
which the Building is located.  Both parties hereto are obligated to obtain such
a waiver and provide evidence to the other party of such waiver.  The waiver set
forth in this Section 7.5 shall be in addition to, and not in substitution for,
any other waivers, indemnities or exclusions of liability set forth in this
Lease.

                                 ARTICLE VIII.
<PAGE>

     Section 8.1  Default by Tenant.  The occurrence of any one or more of the
                  -----------------
following events shall constitute a default by Tenant under this Lease:

     (a)  Tenant shall fail to pay to Landlord any Rent or any other monetary
charge due from Tenant hereunder as and when due and payable;

     (b)  Tenant breaches or fails to comply with any term, provisions,
conditions or covenant of this Lease, other than as described in Section 8.1(a),
                                                                 --------------
or with any of the Building rules and regulations now or hereafter established
to govern the operation of the Project;

     (c)  A Transfer (hereinafter defined) shall occur, without the prior
written approval of Landlord;

     (d)  The interest of Tenant under this Lease shall be levied on under
execution or other legal process;

     (e)  Any petition in bankruptcy or other insolvency proceedings shall be
filed by or against Tenant, or any petition shall be filed or other action taken
to declare Tenant a bankrupt or to delay, reduce or modify Tenant's debts or
obligations or to reorganize or modify Tenant's capital structure or
indebtedness or to appoint a trustee, receiver or liquidator of Tenant or of any
property of Tenant, or any proceeding or other action shall be commenced or
taken by any governmental authority for the dissolution or liquidation of Tenant
and, within thirty (30) days hereafter, Tenant fails to secure a discharge
thereof;

     (f)  Tenant shall become insolvent, or Tenant shall make an assignment for
the benefit of creditors, or Tenant shall make a transfer in fraud of creditors,
or a receiver or trustee shall be appointed for Tenant or any of its properties;
or

     (g)  Tenant shall abandon the Premises or any substantial portion thereof
for any reason other than destruction or condemnation of the Premises.

     Section 8.2  Landlord's Remedies.  Upon occurrence of any default by Tenant
                  -------------------
under this Lease and (i) if the event of default described in Section 8.l(a) is
                                                              --------------
not cured within five (5) days after receipt by Tenant of written notice from
Landlord of such default stating the nature of the default; or (ii) the events
described in Sections 8.1 (b), (d), (f) and (g) are not cured within thirty (30)
             ----------------  ---  ---     ---
days after receipt by Tenant of written notice stating the nature of the default
from Landlord of such default provided that if such default cannot be cured
within thirty (30) days after receipt by Tenant of such notice, Tenant shall not
be in default hereunder so long as Tenant promptly commences curative action
within such thirty (30) day period and thereafter diligently and continuously
pursues such cure to completion within ninety (90) days after delivery of such
notice (there being no notice and cure period for events of defaults described
in Sections 8.1 (c) and (e) except as otherwise set forth herein), the Landlord
   ----------------     ---
shall have the option to do and perform any one or more of the following in
addition to, and not in limitation of, any other remedy or right permitted it by
law or in equity by this Lease:

     (a)  Continue this Lease in full force and effect, and this Lease shall
continue in full force and effect as long as Landlord does not terminate this
Lease, and Landlord shall have the right to collect Rent, Additional Rent and
other charges when due.

     (b)  Terminate this Lease, and Landlord may forthwith repossess the
Premises and be entitled to recover as damages a sum of money equal to the total
of (i) the cost of recovering the Premises, (ii) the cost of removing and
storing Tenant's or any other occupant's property, (iii) the unpaid Rent and any
other sums accrued hereunder at the date of termination, (iv) a sum equal to the
amount, if any, by which the present value of the total Rent and other benefits
which would have accrued to Landlord under this Lease for the remainder of the
Term, if the terms of this Lease had been fully complied with by Tenant,
discounted at five percent (5%) per annum exceeds the total fair market value of
the Premises for the balance of the Term (it being the agreement of the parties
hereto that Landlord shall receive the benefit of its bargain), (v) the cost of
any attempted reletting or reletting and the collection of rent accruing from
such reletting, (vi) the cost of any reasonable brokerage fees or commission
payable by Landlord in connection with any reletting or attempted reletting,
(vii) any other costs reasonably incurred by Landlord in connection with any
such reletting or attempted reletting, (viii) any increase in insurance
<PAGE>

premiums caused by the vacancy of the Premises and (ix) any other sum of money
or damages owed by Tenant to Landlord at law, in equity or hereunder. In the
event Landlord shall elect to terminate this Lease, Landlord shall at once have
all the rights of reentry upon the Premises, without becoming liable for
damages, or guilty of trespass.

     (c)  Terminate Tenant's right of occupancy of the Premises and reenter and
repossess the Premises by entry, forcible entry or detainer suit or otherwise,
without demand or notice of any kind to Tenant and without terminating this
Lease, without acceptance of surrender of possession of the Premises, and
without becoming liable for damages or guilty of trespass, in which event
Landlord may, but shall be under no obligation to, relet the Premises or any
part thereof for the account of Tenant (nor shall Landlord be under any
obligation to relet the Premises before Landlord relets or leases any other
portion of the Project or any other property under the ownership or control of
Landlord) for a period equal to or lesser or greater than the remainder of the
Term of the Lease on whatever terms and conditions Landlord, at Landlord's sole
discretion, deems advisable.  Tenant shall be liable for and shall pay to
Landlord all Rent payable by Tenant under this Lease (plus interest at the past
due rate provided in Section 3.1(c) of this Lease if in arrears) plus an amount
                     --------------
equal to (i) the cost of recovering possession of the Premises, (ii) the cost of
removing and storing any of Tenant's or any other occupant's property left on
the Premises or the Project after reentry, (iii) the cost of decorations,
repairs, changes, alterations and additions to the Premises and the Project,
(iv) the cost of any attempted reletting or reletting and the collection of the
rent accruing from such reletting, (v) the cost of any brokerage fees or
commissions payable by Landlord in connection with any reletting or attempted
reletting, (vi) any other costs incurred by Landlord in connection with any such
reletting or attempted reletting, (vii) the cost of any increase in insurance
premiums caused by the termination of possession of the Premises, (viii) the
amount of any unamortized improvements to the Premises paid for by Landlord,
(ix) the amount of any unamortized brokerage commissions or other costs paid by
Landlord in connection with the leasing of the Premises and (x) any other sum of
money or damages owed by Tenant to Landlord at law, in equity or hereunder, all
reduced by any sums received by Landlord through any reletting of the Premises;
provided, however, that in no event shall Tenant be entitled to any excess of
-----------------
any sums obtained by reletting over and above Rent provided in this Lease to be
paid by Tenant to Landlord.  For the purpose of such reletting Landlord is
authorized to decorate or to make any repairs, changes, alterations or additions
in or to the Premises that may be necessary.  Landlord may file suit to recover
any sums falling due under the terms of this Section 8.2(c) from time to time,
                                             --------------
and no delivery to or recovery by Landlord of any portion due Landlord hereunder
shall be any defense in any action to recover any amount not theretofore reduced
to judgment in favor of Landlord.  No reletting shall be construed as an
election on the part of Landlord to terminate this Lease unless a written notice
of such intention is given to Tenant by Landlord.  Notwithstanding any such
reletting without termination, Landlord may at any time thereafter elect to
terminate this Lease for such previous default and/or exercise its rights under
Section 8.3(b) of this Lease.
--------------

     (d)  Enter upon the Premises and do whatever Tenant is obligated to do
under the terms of this Lease; and Tenant agrees to reimburse Landlord on demand
for any expenses which Landlord may incur in effecting compliance with Tenant's
obligations under this Lease twelve percent (12%) of such cost to cover overhead
plus interest at the past due rate provided in this Lease, and Tenant further
agrees that Landlord shall not be liable for any damages resulting to Tenant
from such action. No action taken by Landlord under this Section 8.2(d) shall
                                                         --------------
relieve Tenant from any of its obligations under this Lease or from any
consequences or liabilities arising from the failure to perform such
obligations.

     (e)  Without waiving such default, apply all or any part of  any unapplied
Prepaid Rent to cure the default or to any damages suffered as a result of the
default to the extent of the amount of damages suffered.  Tenant shall reimburse
Landlord for the amount of such depletion of  any Prepaid Rent on demand.

     (f)  Change all door locks and other security devices of Tenant at the
Premises and/or the Project, and Landlord shall not be required to provide the
new key to the Tenant except during Tenant's regular business hours, and only
upon the condition that Tenant has cured any and all defaults hereunder and in
the case where Tenant owes Rent to the Landlord, reimbursed Landlord for all
Rent and other sums due Landlord hereunder.  Landlord, on terms and conditions
satisfactory to Landlord in its sole discretion, may upon request from Tenant's
employees, enter
<PAGE>

the Premises for the purpose of retrieving therefrom personal property of such
employees, provided, Landlord shall have no obligation to do so.

     (g)  Exercise any and all other remedies available to Landlord in this
Lease, at law or in equity.

     Section 8.3  Waiver of Duty to Relet or Mitigate.  Notwithstanding anything
                  -----------------------------------
contained herein to the contrary, to the full extent permitted under applicable
law, Tenant and Landlord agree that Landlord shall have no duty to relet the
Premises or otherwise mitigate damages under this Lease and Tenant hereby
releases Landlord from any and all duty to relet the Premises or otherwise
mitigate damages.  Tenant agrees that Landlord shall not be liable, nor shall
Tenant's obligations hereunder be diminished, because of Landlord's failure to
relet the Premises or collect rent due with respect to such reletting.
Furthermore, Tenant hereby waives any and all rights to plead such failure of
Landlord to mitigate damages as affirmative defense in any proceeding based on
any Default by Tenant under this Lease.  In the event, and only in the event,
that (despite such waiver and contrary to the intent of the parties hereunder)
applicable law requires Landlord to attempt to mitigate damages, Landlord and
Tenant agree that any such duty to mitigate shall be satisfied and Landlord
shall be deemed to have used objectively reasonable efforts to fill the Premises
by doing the following: (a) posting a "For Lease" sign on the Premises; (b)
advising Landlord's leasing agent of the availability of the Premises; and (c)
advising at least one outside commercial brokerage entity of the availability of
the Premises; provided, however, that Landlord shall not be obligated to relet
              -----------------
the Premises before leasing any other unoccupied portions of the Project and any
other property under the ownership or control of Landlord.  If Landlord receives
any payments from the reletting of the Premises and is required to mitigate
damages (despite the intent of the parties hereunder), any such payment shall
first be applied to any costs or expenses incurred by Landlord as a result of
Tenant's Default under this Lease.

     Section 8.4  Reentry.  If Tenant fails to allow Landlord to reenter and
                  -------
repossess the Premises, Landlord shall have full and free license to enter into
and upon the Premises with or without process of law for the purpose of
repossessing the Premises, expelling or removing Tenant and any others who may
be occupying or otherwise within the Premises, removing any and all property
therefrom and changing all door locks of the Premises.  Landlord may take these
actions without being deemed in any manner guilty of trespass, eviction or
forcible entry or detainer, without accepting surrender of possession of the
Premises by Tenant, and without incurring any liability for any damage resulting
therefrom, including without limitation any liability arising under applicable
state law and without relinquishing Landlord's right to Rent or any other right
given to Landlord hereunder or by operation of law or in equity, Tenant hereby
waiving any right to claim damage for such reentry and expulsion, including
without limitation any rights granted to Tenant by applicable state law.

     Section 8.5  Rights of Landlord in Bankruptcy.  Nothing contained in this
                  --------------------------------
Lease shall limit or prejudice the right of Landlord to prove for and obtain in
proceedings for bankruptcy or insolvency, by reason of the expiration or
termination of this Lease or the termination of Tenant's right of occupancy, an
amount equal to the maximum allowed by any statute or rule of law in effect at
the time when, and governing the proceedings in which, the damages are to be
proved, whether or not the amount be greater, equal to, or less than the amount
of the loss or damages referred to in this Section 8.5. In the event that under
                                           -----------
applicable law, the trustee in bankruptcy or Tenant has the right to affirm this
Lease and continue to perform the obligations of Tenant hereunder, such trustee
or Tenant shall, in such time period as may be permitted by the bankruptcy court
having jurisdiction, cure all defaults of Tenant hereunder outstanding as of the
date of the affirmance of this Lease and provide to Landlord such adequate
assurances as may be necessary to ensure Landlord of the continued performance
of Tenant's obligations under this Lease.

     Section 8.6  Waiver of Certain Rights.  Tenant hereby expressly waives any
                  ------------------------
and all rights Tenant may have under applicable state law to its right to
recover possession of the Premises or terminate this Lease.  Tenant hereby
waives any and all liens (whether statutory, contractual or constitutional) it
may have or acquire as a result of a breach by Landlord under this Lease.
Tenant also waives and releases any statutory lien and offset rights it may have
against Landlord, including without limitation the rights conferred upon
applicable state law.
<PAGE>

     Section 8.7   NonWaiver.  Failure on the part of Landlord to complain of
                   ---------
any action or nonaction on the part of Tenant, no matter how long the same may
continue, shall not be deemed to be a waiver by Landlord of any of its rights
under this Lease.  Further, it is covenanted and agreed that no waiver at any
time of any of the provisions hereof by Landlord shall be construed as a waiver
of any of the other provisions hereof and that a waiver at any time of any of
the provisions hereof shall not be construed as a waiver at any subsequent time
of the same provisions.  The consent or approval by Landlord to or of any action
by Tenant requiring Landlord's consent or approval shall not be deemed to waive
or render unnecessary Landlord's consent or approval to or of any subsequent
similar act by Tenant.

     Section 8.8   Holding Over.  In the event Tenant remains in possession of
                   ------------
the Premises after the expiration or termination of this Lease without the
execution of a new lease, then Tenant, at Landlord's option, shall be deemed to
be occupying the Premises as a tenant at will at a base rental equal to one
hundred fifty percent (150%) of the then applicable Base Rent, and shall
otherwise remain subject to all the conditions, provisions and obligations of
this Lease insofar as the same are applicable to a tenancy at will, including
without limitation the payment of all other Rent; provided, however, nothing
                                                  -----------------
contained herein shall require Landlord to give Tenant more than thirty (30)
days prior written consent to terminate Tenant's tenancy-at-will.  No holding
over by Tenant after the expiration or termination of this Lease shall be
construed to extend or renew the Term or in any other manner be construed as
permission by Landlord to hold over.  Tenant shall indemnify Landlord (y)
against all claims for damages by any other tenant to whom Landlord may have
leased all or any part of the Premises, effective upon the date that is forty-
five (45) days after the date of termination or expiration of this Lease and (z)
for all other losses, costs and expenses, including reasonable attorneys' fees,
incurred by reason of such holding over after such 45th day.

     Section 8.9   Abandonment of Personal Property.  Any personal property left
                   --------------------------------
in the Premises or any personal property of Tenant left about the Project at the
expiration or termination of this Lease, the termination of Tenant's right to
occupy the Premises or the abandonment, desertion or vacating of the Premises by
Tenant, shall be deemed abandoned by Tenant and may, at the option of Landlord,
be immediately removed from the Premises or such other space by Landlord and
stored by Landlord at the full risk, cost and expense of Tenant.  Landlord shall
in no event be responsible for the value, preservation or safekeeping thereof.
In the event Tenant does not reclaim any such personal property and pay all
costs for any storage and moving thereof within thirty (30) days after the
expiration or termination of this Lease, the termination of Tenant's right to
occupy the Premises or the abandonment, desertion or vacating of the Premises by
Tenant, Landlord may dispose of such personal property in any way that it deems
proper.  If Landlord shall sell any such personal property, it shall be entitled
to retain from the proceeds the amount of any Rent or other expenses due
Landlord, together with the cost of storage and moving and the expense of the
sale.  Notwithstanding anything contained herein to the contrary, in addition to
the rights provided herein with respect to any such property, Landlord shall
have the option of exercising any of its other rights or remedies provided in
the Lease or exercising any rights or remedies available to Landlord at law or
in equity.

                                  ARTICLE IX.

     Section 9.1   Transfers.  Tenant shall not, by operation of law or
                   ---------
otherwise, (a) assign, transfer, mortgage, pledge, hypothecate or otherwise
encumber this Lease, the Premises or any part of or interest in this Lease or
the Premises, (b) grant any concession or license within the Premises, (c)
sublet all or any part of the Premises or any right or privilege appurtenant to
the Premises, or (d) permit any other party to occupy or use all or any part of
the Premises (collectively, a "Transfer"), without the prior written consent of
                               --------
Landlord, which consent shall not be unreasonably withheld, conditioned or
delayed.  This prohibition against a Transfer includes, without limitation, (i)
any subletting or assignment which would otherwise occur by operation of law,
merger, consolidation, reorganization, transfer or other change of Tenant's
corporate or proprietary structure; (ii) an assignment or subletting to or by a
receiver or trustee in any federal or state bankruptcy, insolvency, or other
proceedings; (iii) the sale, assignment or transfer of all or substantially all
of the assets of Tenant, with or without specific assignment of Lease; (iv) the
change in control in a partnership; or (v) conversion of Tenant to a limited
liability entity.  If Tenant converts to a limited liability entity without
obtaining the prior written consent of Landlord: (i) the conversion shall be
null and void for purposes of the Lease, including the determination of all
obligations and liabilities of Tenant and its partners to Landlord; (ii) all
<PAGE>

partners of Tenant immediately prior to its conversion to a limited liability
shall be fully liable, jointly and severally, for obligations of Tenant accruing
under this Lease pre-conversion and post-conversion, and all members and other
equity holders in Tenant post-conversion shall be fully liable for all
obligations and liabilities of Tenant accruing under the Lease after the date
such members and other equity holders are admitted to the limited liability
entity as if such person or entity had become a general partner in a
partnership; and (iii) Landlord shall have the option of declaring Tenant in
default under this Lease.  If Tenant requests Landlord's consent to any
Transfer, then Tenant shall provide Landlord with a written description of all
terms and conditions of the proposed Transfer, copies of the proposed
documentation, and the following information about the proposed transferee: name
and address; reasonably satisfactory information about its business and business
history; its proposed use of the Premises; a copy of the proposed sublease or
assignment agreement;  banking, financial and other credit information; and
general references sufficient to enable Landlord to determine the proposed
transferee's creditworthiness and character.  In addition to its right to
approve or reject the proposed Transfer, Landlord shall have the option, upon
written notice to Tenant within thirty (30) days after the receipt of such
information concerning the proposed transferee, to (x) sublease the applicable
space on the terms and conditions of this Lease or (y) in the case of a proposed
assignment or proposed subletting for all or substantially all of the Term, to
terminate this Lease as to the space so affected as of the date of the proposed
assignment or such subletting, in which event the provisions of this Lease
governing such space shall terminate (except for any provisions that pursuant to
this Lease expressly survive such termination); provided, however, that
                                                --------  -------
Landlord's rights set forth in this sentence shall not apply if (A) the proposed
subletting is for less than fifty percent (50%) of the Premises and (B) the
proposed term of such subletting is for less than a four (4) year term
(including any renewal terms). Landlord's consent to a Transfer shall not
release Tenant from performing its obligations under this Lease, but rather
Tenant's transferee shall assume all of Tenant's obligations under this Lease in
a writing satisfactory to Landlord, and Tenant and its transferee shall be
jointly and severally liable therefor.  Landlord's consent to any Transfer shall
not waive Landlord's rights as to any subsequent Transfer.  While the Premises
or any part thereof are subject to a Transfer, Landlord may collect directly
from such transferee all rents or other sums relating to the Premises becoming
due to Tenant or Landlord and apply such rents and other sums against the Rent
and any other sums payable hereunder.  If the aggregate rental, bonus or other
consideration paid by a transferee for any such space exceeds the sum of (y)
Tenant's Rent to be paid to Landlord for such space during such period and (z)
Tenant's costs and expenses actually incurred in connection with such Transfer,
including reasonable brokerage fees, reasonable costs of finishing or renovating
the space affected and reasonable cash rental concessions, which costs and
expenses are to be amortized over the term of the Transfer, then fifty percent
(50%) of such excess shall be paid to Landlord within thirty (30) days after
such amount is earned by Tenant.  Such overage amounts in the case of a sublease
shall be calculated and adjusted (if necessary) on a Lease Year (or partial
Lease Year) basis, and there shall be no cumulative adjustment for the Term.
Landlord shall have the right to audit Tenant's books and records relating to
the Transfer.  Tenant authorizes its transferees to make payments of rent and
any other sums due and payable, directly to Landlord upon receipt of notice from
Landlord to do so.  Any attempted Transfer by Tenant in violation of the terms
and covenants of this Article IX shall be void and shall constitute a default by
                      ----------
Tenant under this Lease.  In the event that Tenant requests that Landlord
consider a sublease or assignment hereunder, Tenant shall pay Landlord's
reasonable attorneys' fees and costs incurred by Landlord in connection with the
consideration of such request or such sublease or assignment.

     Notwithstanding the prohibition against assignment and subleasing contained
in the immediately preceding paragraph, Tenant may, without the prior written
consent of Landlord, but only after giving Landlord at least thirty (30) days
prior written notice (which notice shall include the identity of the Affiliate
(hereinafter defined) and the relationship of the Affiliate to Tenant), sublet
the Premises or any part thereof to an affiliate or assign this Lease to an
Affiliate or permit occupancy of any portion of the Premises by an Affiliate
(each a "Permitted Transfer").  If Tenant is a partnership, the term "Affiliate"
shall mean (i) any corporation which, directly or indirectly, controls or is
controlled by or is under common control with the general partner of Tenant,
(ii) any
<PAGE>

corporation not less than fifty percent (50%) of whose outstanding stock shall,
at the time be owned directly or indirectly by Tenant's general partner or (iii)
any partnership or joint venture in which Tenant or the general partner of
Tenant is a general partner or joint venturer (with joint and several liability
for all of the partnership's or venture's obligations). If Tenant is a
corporation or individual, the term "Affiliate" shall mean (i) any corporation
which, directly or indirectly, controls or is controlled by or is under common
control with Tenant or (ii) any corporation not less than fifty percent (50%) of
whose outstanding stock shall, at the time, be owned directly or indirectly by
Tenant or Tenant's parent corporation. An "Affiliate" shall also include any
entity resulting from the merger, consolidation or other reorganization with
Tenant, whether or not Tenant is the surviving entity or any person or legal
entity which acquires all or substantially all of the assets or stock of Tenant.
Before such transfer shall be effective, (y) in the event of an assignment of
this Lease, said Affiliate shall assume, in full, the obligations of Tenant
under this Lease and (z) the use of the Premises by the Affiliate shall be as
set forth in Section 2.3. For purposes of this paragraph, a public or private
             -----------
offering of Tenant stock is a Permitted Transfer and the term "control" means
the possession, directly or indirectly, of the power to direct or cause the
direction of the management, affairs and policies of anyone, whether through the
ownership of voting securities, by contract or otherwise. The bonus rental
provisions of this Section 9.1 shall not apply to a transfer by Tenant to a
                   -----------
Permitted Transfer. A Permitted Transfer shall not constitute a Transfer for
purposes of this Lease.

     Section 9.2   Assignment by Landlord.  Landlord shall have the right at any
                   ----------------------
time to sell, transfer or assign, in whole or in part, by operation of law or
otherwise, its rights, benefits, privileges, duties, obligations or interests in
this Lease or in the Premises, the Building, the Land, the Project and all other
property referred to herein, without the prior consent of Tenant, and such sale,
transfer or assignment shall be binding on Tenant provided that (i) Tenant is
notified of the transfer and (ii) except as provided in any SNDA, any such
transferee shall assume, in writing, all non-accrued obligations of Landlord
under this Lease.  After such sale, transfer or assignment, Tenant shall attorn
to such purchaser, transferee or assignee, and Landlord shall be released from
all liability and obligations under this Lease accruing after the effective date
of such sale, transfer or assignment.

     Section 9.3   Limitation of Landlord's Liability.  Any provisions of this
                   ----------------------------------
Lease to the contrary notwithstanding, Tenant hereby agrees that no personal,
partnership or corporate liability of any kind or character (including, without
limitation, the payment of any judgment) whatsoever now attaches or at any time
hereafter under any condition shall attach to Landlord or any of Landlord's
Related Parties or any mortgagee for payment of any amounts payable under this
Lease or for the performance of any obligation under this Lease.  The exclusive
remedies of Tenant for the failure of Landlord to perform any of its obligations
under this Lease shall be to proceed against the interest of Landlord in and to
the Project and/or the proceeds of insurance or condemnation.  The provision
contained in the foregoing sentence is not intended to, and shall not, limit any
right that Tenant might otherwise have to obtain injunctive relief against
Landlord or Landlord's successors in interest or any suit or action in
connection with enforcement or collection of amounts which may become owing or
payable under or on account of insurance maintained by Landlord.  In no event
shall Landlord be liable to Tenant, or any interest of Landlord in the Project
be subject to execution by Tenant, for any indirect, special, consequential or
punitive damages.

                                  ARTICLE X.

     Section 10.1  Subordination.  This Lease shall be subject and subordinated
                   -------------
at all times to (a) all ground or underlying leases  which may hereinafter be
executed affecting the Project, and (b) the lien or liens of all mortgages and
deeds of trust in any amount or amounts whatsoever hereafter placed on the
Project or Landlord's interest or estate therein or on or against such ground or
underlying leases and to all renewals, modifications, consolidations,
replacements and extensions thereof and to each advance made or hereafter to be
made thereunder; provided, however, that Tenant obtains from the holder of such
mortgage or deed of trust a Tenant's non-disturbance agreement in such party's
standard form (the "SNDA").  Tenant shall execute and deliver upon demand any
                    ----
instruments, releases or other commercially reasonable documents requested by
any lessor or mortgagee for the purpose of subjecting and subordinating this
Lease to such ground leases, mortgages or deeds of trust, subject to Tenant's
receipt of the SNDA.  Tenant shall, subject to its receipt of the SNDA, attorn
to any party succeeding to Landlord's interest in the Premises, whether by
purchase, foreclosure, deed in lieu of foreclosure, power of sale, termination
of lease or otherwise, only upon such party's request and at such party's sole
discretion but not otherwise.  Notwithstanding such attornment, Tenant agrees
that any such successor in interest shall not be (a) liable for any act or
omission of, or subject to any rights of setoff, claims or defenses otherwise
assertable by Tenant against, any prior owner of the Project (including without
limitation, Landlord), (b) bound by any rents paid more than one (1) month in
advance to any prior owner,  and (d) if such successor is a mortgagee or a
ground lessor whose
<PAGE>

address has been previously given to Tenant, bound by any modification,
amendment, extension or cancellation of the Lease not consented to in writing by
such mortgagee or ground lessor. Subject to Tenant's receipt of the SNDA, Tenant
shall execute all such commercially reasonable agreements confirming such
attornment as such party may reasonably request. Tenant shall not seek to
enforce any remedy it may have for any default on the part of Landlord without
first giving written notice by certified mail, return receipt requested,
specifying the default in reasonable detail, to any mortgagee or lessor under a
lien instrument or lease covering the Premises whose address has been given to
Tenant, and affording such mortgagee or lessor a reasonable opportunity to
perform Landlord's obligations hereunder. Notwithstanding the generality of the
foregoing, any mortgagee or ground lessor may at any time subordinate any such
deeds of trust, mortgages, other security instruments or ground leases to this
Lease on such terms and conditions as such mortgagee or ground lessor may deem
appropriate. Tenant shall execute any such subordination or attornment documents
as described herein within ten (10) days after demand therefor, subject to
Tenant's receipt of the SNDA. Landlord represents and warrants that, as of the
date of this Lease, there is no mortgagee or holder of a deed of trust on the
Project.

     Section 10.2  Estoppel Certificate or Three-Party Agreement.  Tenant agrees
                   ---------------------------------------------
within ten (10) days following written request therefor by Landlord (a) to
execute, acknowledge and deliver to Landlord and any other persons specified by
Landlord, a certificate or three-party agreement among Landlord, Tenant and/or
any third party dealing with Landlord, certifying (i) that this Lease is
unmodified and in full force and effect, or, if modified, stating the nature of
such modification (ii) the date to which the Rent and other charges are paid in
advance, if any, (iii) that there are not, to Tenant's knowledge, any uncured
defaults on the part of Landlord hereunder, or so specifying such defaults, if
any, as are claimed and/or (iv) any other matters as such third party may
reasonably require in connection with the business dealings of Landlord and/or
such third party and (b) to deliver to Landlord current financial statements of
Tenant, including a balance sheet and a profit and loss statement for at least
two (2) years, all prepared in accordance with generally accepted accounting
principles consistently applied.  Tenant's failure to deliver such certificate
or three-party agreement within such ten (10) day period shall be conclusive
upon Tenant (x) that this Lease is in full force and effect without modification
except as may be represented by Landlord, (y) that to Tenant's knowledge there
are no uncured defaults in Landlord's performance, and (z) that no Rent has been
paid in advance except as set forth in this Lease.

     Section 10.3  Notices.  Any Notice, demand, request, consent, approval,
                   -------
disapproval or certificate ("Notice") required or desired to be given under this
                             ------
Lease shall be in writing and given by certified mail, return receipt requested,
by personal delivery or by Federal Express or a similar nationwide over-night
delivery service providing a receipt for delivery.  Notices may not be given by
facsimile.  Notwithstanding anything to the contrary herein, whenever any
provision of the Lease provided the Tenant with a grace period in which to
perform an obligation of Tenant hereunder, such time period shall not commence
until Tenant has actually received (or has refused receipt of) a copy of such
written notice by one of the methods described in this Section 10.3.  Any
                                                       ------------
written notice whose receipt is refused by either Landlord or Tenant shall be
deemed given on the date that such written notice is refused.  All notices,
demands, requests, consents, approvals, disapprovals, or certificates shall be
addressed as follows:

     To Landlord:
     -----------

     DULLES TECH, INC.
     C/o West World Management, Inc.
     4 Manhattanville Road, 2/nd/ Floor
     Purchase, NY 10577

     To Tenant (if prior to Commencement Date):
     -----------------------------------------

     Network Access Solutions Corporation
     100 Carpenter Drive
     Suite 206
     Sterling, VA 20164
     Attn: Manager, Facilities

<PAGE>

     To Tenant (if after Commencement Date):
     --------------------------------------

     Network Access Solutions Corporation
     at the Premises
     Attn: Manager, Facilities

     With a copy to:
     ---------------

     Watt, Tieder, Hoffar & Fitzgerald, L.L.P.
     7929 Westpark Drive, Suite 400
     McLean, Virginia 22102
     Attention: John G. Lavoie, Esquire

Either party may change its address by giving notice of same in accordance with
the methods described in this paragraph reasonably in advance.

                                  ARTICLE XI.

     Section 11.1  Right to Relocate Tenant.  [Intentionally Omitted.]
                   ------------------------

     Section 11.2  Rights and Remedies Cumulative.  The rights and remedies of
                   ------------------------------
Landlord under this Lease shall be nonexclusive and each right or remedy shall
be in addition to and cumulative of all other rights and remedies available to
Landlord under this Lease or at law or in equity.  Pursuit of any right or
remedy shall not preclude pursuit of any other rights or remedies provided in
this Lease or at law or in equity, nor shall pursuit of any right or remedy
constitute a forfeiture or waiver of any Rent due to Landlord or of any damages
accruing to Landlord by reason of the violation of any of the terms of this
Lease.

     Section 11.3  Legal Interpretation.  This Lease and the rights and
                   --------------------
obligations of the parties hereto shall be interpreted, construed and enforced
in accordance with the laws of the state in which the Building is located and
the United States.  The determination that one or more provisions of this Lease
is invalid, void, illegal or unenforceable shall not affect or invalidate any
other provision of this Lease, and this Lease shall be construed as if such
invalid, illegal or unenforceable provision had never been contained in this
Lease, and, so far as is reasonable and possible, effect shall be given to the
intent manifested by the portion held invalid or inoperative.  All obligations
of either party hereunder not fully performed as of the expiration or
termination of the Term of this Lease shall survive the expiration or
termination of the Term of this Lease and shall be fully enforceable in
accordance with those provisions pertaining thereto.  Article and section titles
and captions appearing in this Lease are for convenient reference only and shall
not be used to interpret or limit the meaning of any provision of this Lease.
No custom or practice which may evolve between the parties in the administration
of the terms of this Lease shall waive or diminish the right of Landlord to
insist upon the performance by Tenant in strict accordance with the terms of
this Lease.  This Lease is for the sole benefit of Landlord and Tenant, and,
without the express written consent thereto, no third party shall be deemed a
third party beneficiary hereof.  Tenant agrees that this Lease supersedes and
cancels any and all previous statements, negotiations, arrangements, brochures,
agreements and understandings, if any, between Landlord and Tenant with respect
to the subject matter of this Lease or the Premises and that this Lease,
including written extrinsic documents referred to herein, is the entire
agreement of the parties, and that there are no representations, understandings,
stipulations, agreements, warranties or promises (express or implied, oral or
written) between Landlord and Tenant with respect to the subject matter of this
Lease or the Premises.  It is likewise agreed that this Lease may not be
altered, amended, changed or extended except by an instrument in writing signed
by both Landlord and Tenant.  The terms and provisions of this Lease shall not
be construed against or in favor of a party hereto merely because such party is
the "Landlord" or the "Tenant" hereunder or because such party or its counsel is
the draftsman of this Lease.  All references to days in this Lease and any
Exhibits or Addenda hereto mean calendar days, not working or business days,
unless otherwise stated.

     Section 11.4  Authority.  Each party warrants and represents to the other
                   ---------
that (a) it is a duly organized and validly existing legal entity, in good
standing and qualified to do business in the state in which the Building is
located, with no proceedings pending or contemplated for its dissolution or
reorganization, voluntary or involuntary, (b) it has full right, power and
authority
<PAGE>

to execute, deliver and perform this Lease, (c) the person executing this Lease
on its behalf is authorized to do so, and (d) upon execution of this Lease by
such party, this Lease shall constitute a valid and legally binding obligation
of such party.

     Section 11.5  No Brokers.  Landlord and Tenant warrant and represent to the
                   ----------
other that it has not dealt with any real estate broker and/or salesman (other
than Trammell Crow Real Estate Services, Inc. who represented Landlord and The
Irving Group, who represented Tenant) in connection with the negotiation or
execution of this Lease and no such broker or salesman has been involved in
connection with this Lease, and each party agrees to defend, indemnify and hold
harmless the other party from and against any and all costs, expenses,
attorneys' fees or liability for any compensation, commission and charges
claimed by any real estate broker and/or salesman (other than the aforesaid
brokers) due to acts of such party or such party's representatives.  Landlord
shall pay the brokers identified above pursuant to separate agreements.

     Section 11.6  Consents by Landlord.  In all circumstances under this Lease
                   --------------------
where the prior consent or permission of Landlord is required before Tenant is
authorized to take any particular type of action, such consent must be in
writing and the matter of whether to grant such consent or permission shall,
except as otherwise expressly provided herein, be within the sole and exclusive
judgment and discretion of Landlord, and it shall not constitute any nature of
breach by Landlord under this Lease or any defense to the performance of any
covenant, duty or obligation of Tenant under this Lease that Landlord delayed or
withheld the granting of such consent or permission, whether or not the delay or
withholding of such consent or permission was prudent or reasonable or based
upon good cause.

     With respect to any provision of this Lease which provides that Landlord
shall not unreasonably withhold or unreasonably delay any consent or any
approval, Tenant, in no event, shall be entitled to make nor shall Tenant make
any claim for, and Tenant hereby waives any claim for money damages; nor shall
Tenant claim any money damages by way of setoff, counterclaim or defense, based
upon any claim or assertion by Tenant that Landlord has unreasonably withheld or
unreasonably delayed any consent or approval; but, unless Landlord shall have
acted in bad faith, Tenant's sole remedy shall be an action or proceeding to
enforce any such provision, or for specific performance, injunction or
declaratory judgment.

     Section 11.7  Joint and Several Liability.  If there is more than one
                   ---------------------------
Tenant, then the obligations hereunder imposed upon Tenant shall be joint and
several.

     Section 11.8  Independent Covenants.  The obligation of Tenant to pay Rent
                   ---------------------
and other monetary obligations provided to be paid by Tenant under this Lease
and the obligation of Tenant to perform Tenant's other covenants and duties
under this Lease constitute independent, unconditional obligations of Tenant to
be performed at all times provided for under this Lease, save and except only
when an abatement thereof or reduction therein is expressly provided for in this
Lease and not otherwise, and Tenant acknowledges and agrees that in no event
shall such obligations, covenants and duties of Tenant under this Lease be
dependent upon the condition of the Premises or the Project, or the performance
by Landlord of its obligations hereunder.

     Section 11.9  Attorneys' Fees and Other Expenses.  In the event either
                   ----------------------------------
party hereto defaults in the faithful performance or observance of any of the
terms, covenants, provisions, agreements or conditions contained in this Lease,
the party in default shall be liable for and shall pay to the nondefaulting
party all reasonable expenses incurred by such party in enforcing any of its
remedies for any such default, and if the nondefaulting party places the
enforcement of all or any part of this Lease in the hands of an attorney, the
party in default agrees to pay the nondefaulting party's reasonable attorneys'
fees in connection therewith.

     Section 11.10 Recording.  Neither Landlord nor Tenant shall record this
                   ---------
Lease, but a short- form memorandum hereof may be recorded at the request of
Landlord.

     Section 11.11 Disclaimer; Waiver of Jury Trial.  LANDLORD AND TENANT
                   --------------------------------
EXPRESSLY ACKNOWLEDGE AND AGREE, AS A MATERIAL PART OF THE CONSIDERATION FOR
LANDLORD'S ENTERING INTO THIS LEASE WITH TENANT, THAT, EXCEPT AS OTHERWISE SET
FORTH IN THIS LEASE, (a) LANDLORD HAS MADE NO WARRANTIES TO TENANT AS TO THE
USE OR CONDITION OF THE PREMISES OR THE PROJECT, EITHER EXPRESS OR IMPLIED, AND
(b) LANDLORD
<PAGE>

AND TENANT EXPRESSLY DISCLAIM ANY IMPLIED WARRANTY THAT THE PREMISES OR THE
PROJECT ARE SUITABLE FOR TENANT'S INTENDED COMMERCIAL PURPOSE OR ANY OTHER
WARRANTY (EXPRESS OR IMPLIED) REGARDING THE PREMISES OR THE PROJECT. EXCEPT AS
EXPRESSLY SET FORTH IN THIS LEASE, LANDLORD AND TENANT EXPRESSLY AGREE THAT
THERE ARE NO, AND SHALL NOT BE ANY, IMPLIED WARRANTIES OF MERCHANTABILITY,
HABITABILITY, FITNESS FOR A PARTICULAR PURPOSE OR ANY OTHER KIND ARISING OUT OF
THIS LEASE, ALL SUCH OTHER EXPRESS OR IMPLIED WARRANTIES IN CONNECTION HEREWITH
BEING EXPRESSLY DISCLAIMED AND WAIVED.

          LANDLORD AND TENANT WAIVE THE RIGHT TO A TRIAL BY JURY IN ANY ACTION
OR PROCEEDING BASED UPON, OR RELATED TO, THE SUBJECT MATTER OF THIS LEASE.  THIS
WAIVER IS KNOWINGLY, INTENTIONALLY, AND VOLUNTARILY MADE BY TENANT AND TENANT
ACKNOWLEDGES THAT NEITHER LANDLORD NOR ANY PERSON ACTING ON BEHALF OF LANDLORD
HAS MADE ANY REPRESENTATIONS OF FACT TO INDUCE THIS WAIVER OF TRIAL BY JURY OR
IN ANY WAY TO MODIFY OR NULLIFY ITS EFFECT.  TENANT FURTHER ACKNOWLEDGES THAT IT
HAS BEEN REPRESENTED (OR HAS HAD THE OPPORTUNITY TO BE REPRESENTED) IN THE
SIGNING OF THIS LEASE AND IN THE MAKING OF THIS WAIVER BY INDEPENDENT LEGAL
COUNSEL, SELECTED OF ITS OWN FREE WILL, AND THAT IT HAS HAD THE OPPORTUNITY TO
DISCUSS THIS WAIVER WITH COUNSEL.  TENANT FURTHER ACKNOWLEDGES THAT IT HAS READ
AND UNDERSTANDS THE MEANING AND RAMIFICATIONS OF THIS WAIVER PROVISION AND AS
EVIDENCE OF SAME HAS EXECUTED THIS LEASE.

     Section 11.12  Access to Roof.  At no additional charge by Landlord during
                    --------------
the Term and any renewal thereof, Tenant shall have the sole and exclusive
access to the Building's (i) roof to install, repair and maintain upon the
Building's roof telecommunication devices, such as satellite dishes and antennae
or other similar devices, for the purpose of receiving and sending radio,
television, computer, telephone or other communications signals for its own use
and (ii) risers and conduits in order to connect such telecommunication devices
to the Premises as well as to outside cable, fiber and/or telephone lines,
including easements or rights of way, as reasonably required.  Tenant shall
advise Landlord at least ten (10) days in advance of the planned installation of
such devices which such installation shall be subject to Landlord's prior
approval, which approval shall not be unreasonably withheld, conditioned or
delayed.  Tenant will be responsible for complying and/or obtaining all required
association or governmental approvals or permits with respect to the
installation of the telecommunication devices set forth herein (including
screening of such telecommunication devices if so required).  To the extent that
any telecommunication devices installed by Tenant interferes with other
telecommunication devices installed by Landlord or any of Landlord's tenants at
13600 Dulles Technology Drive, Landlord may require that Tenant relocate, at
Landlord's sole cost and expense, such telecommunication device to another area
of the Building's roof such that it does not interfere with such other
telecommunication device.  Tenant shall remove the telecommunication devices and
any connecting equipment from the Building upon the expiration or earlier
termination of this Lease.  Tenant shall be solely responsible and shall pay for
any damage to the Building arising out of or resulting from the installation,
operation, maintenance and/or removal of the antennae.

     Section 11.13  Parking.  Tenant's occupancy of the Premises shall include,
                    -------
at no additional cost, the use of five hundred thirty-one (531) parking spaces
(at a ratio of 4.7/1000 rentable square feet) which shall be used in common with
other tenants, invitees and visitors of the Building, as shown on Exhibit I
                                                                  ---------
attached hereto.  Tenant shall have access to up to fifteen (15) visitor's
spaces reserved for Tenant's use in locations proximate to the Building mutually
acceptable to Landlord and Tenant. Tenant agrees not to overburden the parking
facilities, to cooperate with Landlord and other tenants in use of the parking
facilities and that neither it nor shall any of its employees, agents or
invitees park any vehicles overnight in the parking facilities. Landlord
reserves the right in its absolute discretion to determine whether the parking
facilities are becoming overburdened and to allocate and reassign parking spaces
among Tenant and other tenants, and to reconfigure the parking area and modify
the existing ingress to and egress from the parking area as Landlord shall deem
reasonably appropriate provided that Tenant continues to have use of and access
to the [five hundred thirty-one (531)] parking spaces set forth above.
<PAGE>

     Section 11.14  No Accord or Satisfaction.  No payment by Tenant or receipt
                    -------------------------
by Landlord of a lesser amount than the Rent and other sums due hereunder shall
be deemed to be other than on account of the earliest Rent or other sums due,
nor shall any endorsement or statement on any check or accompanying any check or
payment be deemed an accord and satisfaction; and Landlord may accept such check
or payment without prejudice to Landlord's right to recover the balance of such
Rent or other sum and to pursue any other remedy provided in this Lease.

     Section 11.15  Acceptance.  The submission of this Lease by Landlord does
                    ----------
not constitute an offer by Landlord or other option for, or restriction of, the
Premises, and this Lease shall only become effective and binding upon Landlord,
upon full execution hereof by Landlord and delivery of a signed copy to Tenant.

     Section 11.16  Waiver of Counterclaim.  Tenant hereby waives the right to
                    ----------------------
interpose any counterclaim of whatever description in any summary proceeding.

     Section 11.17  Time Is of the Essence.  Time is of the essence of this
                    ----------------------
Lease.  Unless specifically provided otherwise, all references to terms of days
or months shall be construed as references to calendar days or calendar months,
respectively.

     Section 11.18  Counterparts.  This Lease may be executed in any number of
                    ------------
counterparts, each of which when so executed and delivered shall be an original,
but such counterparts shall together constitute one and the same instrument.
<PAGE>

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

LANDLORD:
--------

DULLES TECH, INC.,
a Delaware corporation

By: ______________________________________
       Charles Schouten, President

Tax Identification No.:__________________________________

                 [Remainder of Page Intentionally Left Blank.]
<PAGE>

                                   TENANT:
                                   ------

                                   NETWORK ACCESS SOLUTIONS CORPORATION, a
                                   Delaware corporation

                                   By:    ____________________________
                                   Name:  ____________________________
                                   Title: ____________________________

                                   Tax Identification No.:____________________

                 [Remainder of Page Intentionally Left Blank.]
<PAGE>

                                   EXHIBIT A

                           LEGAL DESCRIPTION OF LAND
                           -------------------------
<PAGE>

                                   EXHIBIT B

                            FLOOR PLAN OF PREMISES
                            ----------------------
<PAGE>

                                   EXHIBIT C

                             SPECIAL STIPULATIONS
                             --------------------

     These Special Stipulations are hereby incorporated into this Lease and in
the event that they conflict with any provisions of this Lease, these Special
Stipulations shall control.

     A.   Renewal Options.  1.  If, on the expiration of the Term of this Lease
          ---------------
and the date Tenant notifies Landlord of its intention to renew the Lease Term
(as provided in subsection (2) below), (i) Tenant is not in default under this
Lease beyond any applicable notice and cure period provided for in this Lease,
and (ii) this Lease is in full force and effect, then Tenant shall have and may
exercise an option to renew this Lease for an additional term of five (5) years
(the "Renewal Term") upon the same terms and conditions contained in this Lease
      ------------
with the exceptions that the rental for the Renewal Term shall be the then-
prevailing market rate of rent in the Herndon, Virginia area, inclusive of
consideration of then-current market concessions (including, without limitation,
refurbishment allowances and rent abatement) (the "Renewal Rental Rate").
                                                   -------------------

     2.   If Tenant desires to renew this Lease pursuant to subsection (1)
above, Tenant must notify Landlord in writing of its intention to renew (the
"Renewal Notice") not less than twelve (12) months prior to the expiration of
 --------------
the Term of this Lease (the "Expiration Date").  Landlord shall, within ten (10)
                             ---------------
business days following the later of Landlord's receipt of such Renewal Notice
or the date which is twelve (12) months prior to the Expiration Date, notify
Tenant in writing of Landlord's determination of the Renewal Rental Rate and
Tenant shall, within the next ten (10) business days following receipt of
Landlord's determination of the Renewal Rental Rate, notify Landlord in writing
of Tenant's acceptance or rejection of Landlord's determination of the Renewal
Rental Rate.  If Tenant timely notifies Landlord of Tenant's acceptance of
Landlord's determination of the Renewal Rental Rate, this Lease shall be
extended as provided herein and Landlord and Tenant shall enter into an
amendment to this Lease to reflect the extension of the Lease Term and changes
in Base Rent in accordance with this Exhibit.  If (i) Tenant timely notifies
Landlord in writing of Tenant's rejection of Landlord's determination of the
Renewal Rental Rate or (ii) Tenant does not notify Landlord in writing of
Tenant's acceptance or rejection of Landlord's determination of the Renewal
Rental Rate within such ten (10) business day period, Landlord and Tenant will
promptly attempt to agree on the Renewal Rental Rate.  If Landlord and Tenant
cannot agree within ten (10) business days of Tenant's rejection in subclause
(i) hereinabove or the expiration of the ten (10) business days period referred
to in subclause (ii) hereinabove, then Tenant may either (A) withdraw its
Renewal Notice by written notice to Landlord, in which event, all of Tenant's
rights under this Paragraph A shall immediately and irrevocably terminate, or
(B) proceed promptly to determine the Renewal Rental rate by appraisal, in which
case, Landlord and Tenant shall each select a qualified independent real estate
broker or appraiser (i.e., a real estate broker or appraiser with no prior or
existing  contractual relationship with either party) with at least five (5)
years experience in leasing office buildings in the Herndon, Virginia area to
determine the Renewal Rental Rate.  If the values determined by the
brokers/appraisers are less than ten percent (10%) apart, the average of the
values determined by them shall be deemed the Renewal Rental Rate for the
Premises.  If the brokers/appraisers do not agree, and if their determinations
are more than ten percent (10%) apart, then on or before seventy-five (75) days
prior to the commencement of the Renewal Term, the two brokers/appraisers shall
select a third independent broker/appraiser who will determine the Renewal
Rental Rate for the Premises.  If the value determined by the third
broker/appraiser is between the values determined by the two prior
broker/appraisers, the determination of the third broker/appraiser will control.
If the third broker/appraiser's determination is not between the values
determined by the two prior broker/appraisers, then the value of the first two
broker/appraisers closest to the value of the third broker/appraiser will be the
Renewal rental Rate for the Premises.  Each party shall pay the fees and
expenses of its broker/appraiser, and the fees and expenses of the third
broker/appraiser shall be shared equally between Landlord and Tenant.

     B.   Landlord Lien Waiver.  Landlord hereby waives any lien rights which it
          --------------------
may otherwise have concerning Tenant's property, which shall include furniture,
fixtures, equipment, any and all equipment and/or supplies utilized by Tenant in
its business operations, and Tenant
<PAGE>

shall have the right to remove the same at any time without Landlord's consent.
Furthermore, Landlord acknowledges Tenant's right to finance and to secure under
the Uniform Commercial Code, inventory, furnishings, furniture, equipment,
machinery, leasehold improvements and other personal property located in or at
the Premises, and Landlord agrees to execute commercially reasonable waiver
forms releasing liens in favor of any purchase money seller, lessor or lender
who has financed or may finance in the future such items. Without limiting the
effectiveness of the foregoing, provided that no default shall have occurred and
be continuing, Landlord shall, upon the request of Tenant, and at the Tenant's
sole cost and expense, execute and delivery any commercially reasonable
instruments necessary or appropriate to confirm any such grant, release,
dedication, transfer, annexation or amendment to any person or entity permitted
under this paragraph including landlord waivers with respect to any of the
foregoing.
<PAGE>

                                   EXHIBIT D

                          COMMENCEMENT DATE AGREEMENT
                          ---------------------------

     This Commencement Date Agreement (this "Agreement") is made and entered
                                             ---------
into this ____day of ___________, 19___, by and between DULLES TECH, INC.

("Landlord") and NETWORK ACCESS SOLUTIONS ("Tenant").
----------                                  ------

     WHEREAS, Landlord and Tenant entered into that certain Lease (the "Lease")
                                                                        -----
dated October ___, 1999, with respect to certain premises located at 13650
Dulles Technology Drive, Herndon, Virginia 20171, as such demised premises are
more particularly described in the Lease.

     WHEREAS, this Agreement is executed by Landlord and Tenant to confirm the
Commencement Date and the Expiration Date, as those terms are defined in the
Lease;

     NOW, THEREFORE, for and in consideration of the demised premises and the
mutual covenants expressed in the Lease, it is hereby agreed by Landlord and
Tenant as follows:

          1.   The Premises were substantially complete and the Base Rent and
Additional Rent (as such terms are defined in the Lease) commenced on
_____________, 19__ (the "Commencement Date") and will expire on ___________,
                          -----------------
20 ___ (the "Expiration Date").
            ---------------

          2.   This Agreement shall not be deemed or construed to alter or amend
the Lease in any manner.

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

                               LANDLORD
                               --------

                                    DULLES TECH, INC., a Delaware corporation

                                    By:  ________________________________
                                    Charles Schouten, President

                                    TENANT:
                                    ------

                               NETWORK ACCESS SOLUTIONS CORPORATION,
                                    a Delaware corporation

                                    By:    ______________________________
                                    Name:  ______________________________
                                    Title: ______________________________
<PAGE>

                                   EXHIBIT E

                    WORK LETTER AGREEMENT ("WORK AGREEMENT")
                    ----------------------------------------

     The following provisions shall govern (A) the preparation and approval
process for the drawings and specifications for the build-out of the Premises
and (B) terms and conditions relating to contractors and subcontractors in
connection with the build-out of the Premises.

     A.   Description of Landlord's Work.  Subject to the terms and conditions
          ------------------------------
of this Work Agreement, Landlord agrees to construct, at its sole cost and
expense, a building shell which shall contain the following items ("Landlord's
                                                                    ----------
Work"):
----

          As described in Landlord's October 15, 1999 proposal attached hereto
in Exhibit E-2 with the following additions:
   -----------

          1)   All concrete flooring should be level, complete and ready to
accept carpet, VCT or other floor applications.

          2)   The base Building should have an energy management system of a
quality found in similar class buildings in Reston/Herndon, Virginia submarket.

     B.   General Matters regarding Plans and Specification.  Tenant shall cause
          -------------------------------------------------
its architect (The M Group, except as otherwise set forth in this Work
Agreement) and/or engineer (B&A Consulting Engineers, except as otherwise set
forth in this Work Agreement) to prepare "Tenant's Space Plans", the "Working
Drawings" and the "Final Plans" (as such terms are defined below) for the Tenant
Improvement Work.  The fees of Tenant's architect and engineer shall be paid by
Landlord from the "Tenant Improvement Allowance", as defined below.

     C.   Tenant Improvement Work.  (1)  Tenant shall submit to Landlord for
          -----------------------
Landlord's approval a space plan for the build-out of the Premises ("Tenant's
                                                                     --------
Space Plans"), by the respective date(s) for each phase shown on the
-----------
construction schedule set forth in Exhibit E-1 hereto, prepared by Tenant's
                                   -----------
architect showing the interior layout of the Premises and its integration with
Building systems, core areas and the building shell improvements in sufficient
detail to permit Landlord a reasonable opportunity to review and provide
preliminary approval or comments regarding Tenant's proposed interior design.
Landlord shall review and approve or disapprove of Tenant's Space Plans as to
the First Phase Premises and Second Phase Premises by the date set forth on the
attached construction schedule set forth in Exhibit E-1 hereto, which approval
                                            -----------
shall not be unreasonably withheld, conditioned or delayed, except or to the
extent such plans affect the structure of the Building or the Building's
systems, in which case, Landlord may withhold such approval in its sole
discretion.  Landlord shall endeavor to adhere to a similar construction
schedule, review periods and level of cooperation with Tenant as to the
planning, approving and completion of the Third Phase Premises thereafter.  If
Landlord disapproves, either in whole or in part, of Tenant's Space Plans,
Landlord shall provide to Tenant with reasonable specificity Landlord's reasons
for its disapproval, which shall be commercially reasonable to the extent
required in the preceding sentence.  Tenant shall promptly correct or otherwise
address all disapproved items identified by Landlord.  The work shown in
Tenant's Space Plans shall be deemed "Tenant Improvement Work."  (2)  Landlord
                                      -----------------------
and Tenant hereby covenant and agree that Rent pursuant to the Lease shall
commence for each phase of construction upon substantial completion of all
Tenant Improvement Work  ("Substantial Completion") as defined pursuant to
                           ----------------------
Section (L) below so that Tenant could obtain its Certificate of Occupancy and
occupy each phase of the Premises then intended for occupancy.  For every day
after March 1, 2000 that such First Phase Premises are not Substantially
Complete, absent any delay on the part of the Tenant or any occurrence of Force
Majeure, Landlord shall pay to Tenant as a fixed and agreed upon sum and not as
a penalty, an amount equal to one (1) day's rent for the First Phase Premises
for each day after March 1, 2000 that the Tenant is unable to occupy the First
Phase Premises because the same is not Substantially Complete.  Notwithstanding
the foregoing, there shall be no Force Majeure condition excusing Landlord from
its obligation to pay the damages specified herein if Landlord is delayed due to
its inability to procure sufficient labor, either for its general contractor,
its subcontractors, its Construction Manager, or any other entity, required to
complete the First Phase or the Second Phase.  Landlord
<PAGE>

shall pay to Tenant such amounts in immediately available U.S. funds monthly at
the end of each month unless and until the First Phase Premises are
Substantially Complete.

     D.   Working Drawings and Final Plans.  Tenant shall cause its architects
          --------------------------------
and/or engineers to prepare, and Tenant shall submit to Landlord, complete
preliminary architectural plans, construction drawings and mechanical,
electrical and plumbing drawings for the Premises (the "Working Drawings"),
                                                        ----------------
including those base Building improvements (such as HVAC and sprinkler
distribution and the like) which are interior to the Premises or otherwise need
to be coordinated with Landlord's Work in order to be performed properly.  Said
Working Drawings shall be submitted to Landlord in form sufficient for the
permitting and construction of the Premises, and the bidding of the Tenant
Improvement Work (that is, in such form so that, if approved by Landlord without
revision, the same would be sufficient for the permitting and construction of
the Premises, and the bidding of the Tenant Improvement Work).  Within five (5)
business days, Landlord or its designated contractor shall provide Tenant with a
list of its objections, modifications, deletions or qualifications to the same.
Tenant shall cause Tenant's architect and engineer to prepare final drawings,
plans, and specifications (the "Final Plans"), based on the Working Drawings but
                                -----------
conforming to Landlord's objections, modifications, deletions or qualifications
which shall be commercially reasonable to the extent required hereunder, by the
date set forth on the attached construction schedule set forth in Exhibit E-1
                                                                  -----------
hereto.  No plans and specifications shall constitute the Final Plans hereunder
unless and until the same have been acknowledged, approved and agreed in writing
as to the exact description, detail and date of the Final Plans by both Landlord
and Tenant.  Such acknowledgment shall be attached hereto as Exhibit E-3.
                                                             -----------
Landlord agrees to respond to Tenant within five (5) business days of Tenant's
written request for Landlord's approval.  If Landlord fails to respond with the
five (5) business days period, Tenant may deliver a second request for approval;
if Landlord does not respond within five (5) business days of delivery of such
second notice, then Landlord's approval shall be deemed granted.

     E.   Construction.  Following the preparation and approval of Tenant's
          ------------
Space Plans and the Working Drawings, Landlord agrees to build out the Premises
according to the Final Plans.  All construction for the Premises shall be
awarded following a competitive bid format, with Trammell Crow Company serving
as construction manager ("Construction Manager").  The Construction Manager
                          --------------------
shall: (1) prepare a bid package approved by Landlord and Tenant; (2) solicit
bids from a minimum of three (3) qualified general contractors approved by
Landlord and Tenant; (3) prepare a bid analysis for review by Landlord and
Tenant; and (4) award the bid to the lowest qualified general contractor which
such contractor shall be subject to Tenant's reasonable approval.  On behalf of
Landlord and Tenant, the Construction Manager shall supervise the construction
for the Premises.

     F.   Tenant Improvement Allowance.  Landlord agrees to provide to Tenant an
          ----------------------------
allowance with respect to the Premises of Twenty Five Dollars ($25.00) per
rentable square foot (the "Tenant Improvement Allowance") (i.e., a total of
                           ----------------------------
113,093 sf x $25.00 prsf = Two Million Eight Hundred Twenty Seven Three Hundred
Twenty Five Dollars ($2,827,325.00).  Any unused portion of the Tenant
Improvement Allowance shall be applied against any move related costs including
any cabling requirements, antenna or signage costs, and any further remaining
allowances may be used to offset rent throughout the Term or any renewal term.
Provided Tenant uses The M Group as its architect to perform Tenant's Space
Plans, Working Drawings or Final Plans, except as to the network and/or
telecommunications operations center, Landlord's three percent (3%) construction
management fee shall be charged only against hard construction costs.

     G.   Delay in Preparation of Tenant's Space Plans.  If  a "Tenant Delay"(as
          --------------------------------------------          ------------
defined below) occurs, and Substantial Completion of the Premises is delayed as
a result thereof, then Tenant shall pay to Landlord on the date Rent would have
commenced hereunder in the absence of such delay, a sum of money equivalent to
the Rent for the Premises for the period during which Tenant would have been
obligated to pay Rent to Landlord had not the Commencement Date been so delayed;
provided, however, that Landlord shall have notified Tenant in writing that a
--------  -------
Tenant Delay has occurred, which such notice shall describe the nature of the
Tenant Delay, within five (5) business days following Landlord's learning about
the Tenant Delay.  Each Tenant Delay shall be offset against each day Landlord
fails to Substantially Complete Landlord's Work due to a Landlord Delay (as
defined below).
<PAGE>

     H.   Changes to Tenant Plans.  Tenant shall have the right to request
          -----------------------
changes in the Final Plans and any such change shall be initiated by Tenant's
architect and approved by Landlord, which approval shall not be unreasonably
withheld, conditioned or delayed (except for changes which affect the structure
of the Building or the Building's systems, in which case Landlord may withhold
its consent in its sole discretion) and reasonably approved by the general
contractor.  Further, if changes are made by Tenant to the Final Plans after
Landlord's approval, and should these changes to Tenant's Final Plans cause
Landlord to fail to achieve Substantial Completion of the Premises by the dates
specified herein or delay the Commencement Date, then Landlord shall have the
right to refuse to permit the making of such changes unless and until Tenant
shall have committed in writing, in a manner reasonably satisfactory to
Landlord, to pay to Landlord on the date Rent would have commenced hereunder in
the absence of such delay, a sum of money equivalent to the Rent for the
applicable phase of the Premises for the period during which Tenant would have
been obligated to pay Rent to Landlord had not this Lease Commencement Date been
so delayed.

     I.   Tenant's Work.  Notwithstanding anything to the contrary in this
          -------------
Exhibit E, Tenant shall be responsible for all work, construction and
---------
installation in the Premises which is not designated as Landlord's Work and
Tenant Improvement Work (including but not limited to all fixtures, furniture,
equipment and other office installations).  Such work shall be referred to as
"Tenant's Work," and shall be at Tenant's sole cost and expense subject to the
 -------------
application of the Tenant Improvement Allowance.  Tenant's Work shall be
considered an alteration for purposes of this Lease, and shall be subject to the
provisions of Section 6.1 thereof.  Notwithstanding the foregoing, any plans
              -----------
Tenant has attached hereto as Exhibit E-4 as of the date this Lease is executed
                              -----------
depicting such Tenant Work are hereby deemed approved by Landlord.  Prior to
commencing any other Tenant's Work, Tenant shall submit drawings and
specifications for Tenant's Work to Landlord, showing all aspects of such work,
to Landlord for Landlord's review and approval, which approval as to non-
structural matters and matters not affecting the Building's systems shall not be
unreasonably withheld, conditioned or delayed.  In order to perform the Tenant's
Work, upon Tenant's notice (reasonably sufficient to permit Landlord to
supervise Tenant's Work), Landlord shall grant Tenant, its contractors and
agents access to the extent permitted by law to the Building, loading dock, and
a dedicated elevator for freight use during the hours of 6:00 a.m. to 6:00 p.m.
and 8:00 a.m. to 1:00 p.m. on Saturday (except as to Tenant's move-in which
shall be over one or more weekends and the hours adjusted accordingly to
accommodate Tenant's scheduled move) and such additional time as may be
reasonably agreed between Landlord and Tenant subject to compliance with the
Building Rules and Regulations set forth in Exhibit F to the Lease, from the
                                            ---------
time the Lease is executed and further during the move-in phases related to the
Tenant Work or the Premises.  Furthermore, Landlord, shall grant access to and
normal and customary use of reasonable temporary utilities including, but not
limited, to electricity, HVAC, plumbing and water, during such stated hours and
such additional time as may be agreed between Landlord and Tenant.  Tenant
agrees that it will pay Landlord directly for the actual portion of utilities
used by Tenant in the Project to construct the Tenant Work within thirty (30)
days after written request accompanied by presentation and verification of
documented costs and charges for such utility usage.  Tenant agrees that such
entry into the Premises shall be deemed to be under all of the terms, covenants,
conditions and provisions of the Lease, except that the covenant to pay periodic
Rent shall not apply until the Lease Commencement Date.  Tenant acknowledges
that the Landlord Work and Tenant Improvement Work take precedence over the
completion of the Tenant's Work, but Landlord shall reasonably cooperate with
Tenant as to the scheduling and completion of the Tenant's Work.

     J.   Permits, Certificate of Occupancy.  Except as provided below, Landlord
          ---------------------------------
shall obtain all necessary permits in connection with Landlord's Work and Tenant
Improvement Work.  On or before the date Landlord tenders delivery of the
Premises to Tenant, Landlord agrees to obtain all final inspection approvals
which are required for Landlord to deliver the Premises to Tenant with
Landlord's Work completed, and to obtain all Certificates of Occupancy, pursuant
to Section (L) hereof, that can be obtained by Landlord prior to Tenant
   -----------
installing its fixtures, furniture and equipment.  Tenant shall be responsible
for applying for and obtaining all permits required for Tenant to perform
Tenant's Work, and for obtaining the final fire inspection approval after
installation of Tenant's Work, if any.

     K.   Notice.  Tenant and Landlord shall, by notice to the other in writing,
          ------
designate a single individual who Tenant or Landlord agrees shall be available
to meet and consult with the other at the Premises as Tenant's or Landlord's
representative respecting the matters which are
<PAGE>

the subject of this Exhibit and who, as between Landlord and Tenant, shall have
the power to legally bind Tenant and Landlord, in making requests for changes,
giving approval of plans or work, giving directions to Tenant and Landlord or
the like, under this Exhibit (each of these representatives shall be a
"Construction Representative"); provided, however, that Landlord's Construction
 ---------------------------
Representative shall not have authority to approve changes without Landlord's
prior approval.

     L.   Substantial Completion.  For purposes of this Lease, "Substantially
          ----------------------                                -------------
Complete" or "Substantial Completion" as to the Premises or the applicable phase
--------      ----------------------
thereof means full completion, except for minor or insubstantial details of
construction, decoration or installation such that a Certificate of Occupancy
has been issued for Landlord's Work and Tenant Improvement Work to the extent
that the same can be issued prior to the completion of Tenant's Work, if any.
In the event that Landlord is unable to obtain a Certificate of Occupancy due to
unfinished Tenant's Work which is not delayed due to Landlord, Landlord shall be
deemed to have achieved Substantial Completion when Landlord obtains final and
complete trade inspections for all major trades.  Landlord shall use
commercially reasonable efforts to give Tenant at least ten (10) business days
prior written notice of the date that the Premises, or the applicable phase
thereof, will be Substantially Complete.

     M.   Permits; Compliance with Laws.  The Tenant's Space Plans shall be in a
          -----------------------------
form in which building permits can be readily obtained and shall comply with all
applicable local, state and federal laws, ordinances, codes and regulations.
The architect shall certify to Landlord and Tenant that Tenant's Space Plans
comply with the Americans with Disabilities Act of 1990 ("ADA") and all other
                                                          ---
applicable local, state and federal laws, ordinances, codes and regulations.

     N.   Default.  The failure by Landlord or Tenant to comply with the
          -------
provisions of this Exhibit E shall constitute a default by that respective
                   ---------
entity under the Lease and the non-defaulting party shall have the benefit of
all remedies provided for in the Lease.

     O.   No Liability. Notwithstanding the review and approval by Landlord of
          ------------
Tenant's Space Plans and specifications, Landlord shall have no responsibility
or liability in regard to the safety, sufficiency, adequacy or legality thereof
and Tenant shall be solely responsible for the compliance of such plans and
specifications with all applicable laws and regulations, the architectural
completeness and sufficiency thereof and other matters relating thereto, except
to the extent a valid construction permit is issued therefore.

     P.   Code Compliance.  Landlord shall construct the base Building Landlord
          ---------------
Work so that it is in compliance with all applicable codes and laws, including
the ADA.

     Q.   Back-Up Generator.  Landlord shall provide a location mutually
          -----------------
acceptable to Landlord and Tenant for the location of a generator to be
installed by Tenant (the costs of which may be deducted from the Tenant
Improvement Allowance) to provide back up power and for any supplemental HVAC
equipment that will be required. The generator shall be reasonably screened and
buffered as required; the costs of which may be deducted from the Tenant
Improvement Allowance.

     R.   Network and/or Telecommunications Operations Center.  Tenant shall
          ---------------------------------------------------
have an approximately nine thousand three hundred sixty two (9,362) square feet
network and/or telecommunications operations center in the Building that will
operate twenty four (24) hours per day, seven (7) days per week, that will be
contained within the Third Phase Premises. Landlord and Tenant shall work
together to achieve the most cost effective method to accommodate this need.
Tenant may utilize at no additional cost the base Building condenser water riser
system for its supplement HVAC equipment. Notwithstanding anything else in this
Lease, Tenant shall have the right, subject to Landlord's reasonable approval,
to choose its architect, engineer, consultants, general contractor and
subcontractors to perform this work.

     S.   Landlord Delays or Tenant Delays. 1.  As used herein, "Landlord Delay"
          --------------------------------                       --------------
shall mean a delay which is primarily attributable to one or more of the
following:

          (a)  Landlord's (for purposes of this Exhibit E, "Landlord" shall be
                                                ---------
               deemed to include the Landlord, Landlord's Construction
               Representative, Landlord's consultants, the general contractor
               and the agents of all of these), (i) failure to comply with any
               of the deadlines specified in this Work Agreement, (ii)
<PAGE>

               unjustifiably withholding, delaying or refusal to (A) fund, or
               permit to be funded by Tenant, any draw request of the Tenant
               Improvement Allowance, or (b) make any advance or grant any
               approval requested by Tenant relating to the Tenant Space Plans,
               Working Drawings or Final Plans, Landlord Work, Tenant
               Improvement Work or Tenant Improvement Allowance as indicated by
               Tenant prevailing in the dispute resolution process described in
               Section (W) hereof, or (iii) Landlord's breach of its obligations
               -----------
               under the terms of this Work Agreement or the Lease;

          (b)  Landlord's request for changes or additions to the Final Plans
               for the Tenant Improvement Work subsequent to the date of
               Landlord's approval of the Final Plans and not related to Tenant
               Final Plan changes;

          (c)  The gross negligence or willful misconduct of Landlord, in
               connection with the Landlord Work, Tenant Improvement Work or
               this Work Agreement;

          (d)  Landlord's unreasonable interference with the Tenant's schedule
               for Tenant Work or the general contractor's schedule for the
               Landlord Work or Tenant Improvement Work; or

          (e)  The time and delay incurred by the enforcement of the dispute
               resolution process outlined in Section (W) to this Work
               Agreement, to the extent that Tenant is the prevailing party
               therein.

     2.   As used herein, "Tenant Delay" shall mean a delay which is primarily
                           ------------
attributable to one or more of the following:

               a.   Tenant's (for purposes of this Exhibit E, "Tenant" shall be
                                                   ---------
          deemed to include the Tenant, Tenant's Construction Representative,
          Tenant's consultants and the agents of all of these), (i) failure to
          comply with any of the deadlines specified in this Work Agreement,
          (ii) unjustifiably withholding, delaying or refusing to make any
          approval sought by Landlord or (iii) breach of its obligations under
          the terms of this Work Agreement or the Lease;

               b.   Tenant's request for changes or additions to the Final Plans
          after Landlord's approval of same that cause Landlord to fail to
          achieve Substantial Completion of the Premises by the dates specified
          herein;

               c.   The gross negligence or willful misconduct of Tenant, in
          connection with the submittal of Tenant's Space Plans and Working
          Drawings, Tenant's Work or this Work Agreement;

               d.   Tenant's unreasonable interference with the Landlord's or
          general contractor's schedule for Landlord Work or Tenant Improvement
          Work;

               e.   The time and delay incurred by the enforcement of the
          dispute resolution process outlined in Section (W) to this Work
          Agreement, to the extent that Landlord is the prevailing party.

     T.   Access. [Intentionally Deleted.]
          ------

     U.   Adjustment of Tenant Improvement Allowance.  At such time as the exact
          ------------------------------------------
square footage of the Premises is determined in accordance with Section 2.1 of
the Lease, then in that event the Tenant Improvement Allowance shall be adjusted
to reflect the correct amounts based upon the re-computed and agreed upon
rentable square footage of the Premises.

     V.   Time for Performance.  Wherever in this Work Agreement a date for
          --------------------
performance falls on a Saturday, Sunday or legal holiday, the time for
performance shall be extended until the following business day.

     W.   Disputes.  In the event that either party shall have any claim or
          --------
dispute under this Exhibit E, both parties agree that such claim or dispute
                   ---------
shall be decided by arbitration in
<PAGE>

accordance with the Construction Industry Rules of the American Arbitration
Association. Both parties irrevocably submit to such arbitration. Both parties
further agree that any decision so rendered through that arbitration shall be
final and binding on both parties hereto and may be entered in any court of
competent jurisdiction.

                               List of Exhibits
                               ----------------

Exhibit E-1  Schedule
-----------

Exhibit E-2  Completed Shell Definitions
-----------

Exhibit E-3  Written Confirmation of Tenant's Final Plans
-----------

Exhibit E-4  Tenant's Work
-----------
<PAGE>

                                  EXHIBIT E-1
                                  -----------

<TABLE>
<CAPTION>
                                                           First Phase        Second Phase
                                                           --------------------------------
Tenant Executes Lease Document                             Oct 27,1999        Oct 27, 1999
-------------------------------------------------------------------------------------------
<S>                                                        <C>                <C>
Tenant to submit approved Space Plan to Landlord for       Nov 5, 1999        Dec 6, 1999
review.
Tenant to submit completed load letter to Landlord.        Nov 5, 1999        Dec 6, 1999
Landlord to complete review and approve or disapprove      Nov 9, 1999        Dec 9, 1999
Tenant Space Plan
Tenant to submit approved Construction Drawings and        Nov 19, 1999       Dec 20, 1999
Specifications to Landlord for review.
Landlord to complete review and approve or disapprove      Nov 23, 1999       Dec 23, 1999
Tenant Construction Drawings and Specifications.
Landlord to submit for Building Permit.                    Nov 23, 1999       Dec 23, 1999
Landlord to send construction bid packages to general      Nov 23, 1999       Dec 23, 1999
contractors.
General contractors' bids due                              Dec 14, 1999       Jan 13, 2000
Construction Bid acceptance date (LL awards to low,        Dec 17, 1999       Jan 17, 2000
qualified general contractor)
Construction Start Date                                    Dec 20, 1999       Jan 19, 2000
Building Permit approved by Fairfax County                 Jan 3, 2000        Feb 2, 2000
General contractor to submit for sprinkler & fire alarm    _____________      _____________
Permits.
Fairfax County approves sprinkler & fire alarm permits     _____________      _____________
Target Date for Substantial Completion                     March 1, 2000      April 1, 2000
</TABLE>
<PAGE>

                                  EXHIBIT E-2

                          COMPLETED SHELL DEFINITIONS
                          ---------------------------
<PAGE>

                                  EXHIBIT E-3

                 WRITTEN CONFIRMATION OF TENANT'S FINAL PLANS
                 --------------------------------------------

               [TO BE ATTACHED SUBSEQUENT TO LEASE SIGNING UPON
                   MUTUAL AGREEMENT OF LANDLORD AND TENANT]
<PAGE>

                                  EXHIBIT E-4

                                 TENANT'S WORK
                                 -------------

               [TO BE ATTACHED SUBSEQUENT TO LEASE SIGNING UPON
                   MUTUAL AGREEMENT OF LANDLORD AND TENANT]
<PAGE>

                                   EXHIBIT F

                        BUILDING RULES AND REGULATIONS
                        ------------------------------

1.   Sidewalks, doorways, vestibules, halls, stairways, and other similar areas
shall not be used for the disposal of trash, be obstructed by Tenant or be used
by Tenant for any purpose other than ingress and egress to and from the Premises
and for going from one part of the Building to another part of the Building.

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 therein. Damage resulting to any such fixtures or
appliances from misuse by Tenant shall be paid by such Tenant and Landlord shall
not in any case be responsible therefor.

3.   Signs, advertisements, or notices visible in or from public corridors or
from outside the Building shall be subject to Landlord's prior written approval.
Without Landlord's prior consent, which consent shall not be unreasonably
withheld, no curtains or other window treatments shall be placed between the
glass and the Building standard window treatments.

4.   With respect to work being performed by Tenant in the Premises, Tenant
shall refer all contractors, contractors' representatives, and installation
technicians rendering any service to Tenant to Landlord for Landlord's
supervision and approval before the performance of any contractual services.
This provision shall apply to all work performed in the Building, including, but
not limited to, installations of telephones, telegraph equipment, electrical
devices and attachments, and any and all installations of every nature affecting
floors, walls, woodwork, trim, windows, ceilings, equipment, and other physical
portions of the Building.

5.   Movement in or out of the Building of furniture, office equipment, safes
and other heavy equipment, or the dispatch or receipt by Tenant of any bulky
material or merchandise, or materials which require use of elevators or
stairways or movement through the Building entrances or lobby, shall be
restricted to such hours as Landlord reasonably designates. All such movement
shall be under the supervision of Landlord and in the manner reasonably agreed
between Tenant and Landlord by prearrangement before performance. Such
prearrangement, to be initiated by Tenant, will include reasonable determination
by Landlord as to the time, method, and routing of such movement and as to
limitations for safety or other concerns. Tenant assumes all risks of damage to
articles moved and injury to persons engaged or not engaged in such movement.
Tenant shall be liable to personnel of Landlord damaged or injured as a result
of acts in connection with carrying out this service for Tenant, and Landlord
shall not be liable for the acts of any person engaged in, or any damage or loss
to any property or persons resulting from any act in connection with, such
service performed for Tenant.

6.   Building management shall have the right and authority to prescribe the
maximum weight and position of safes and other heavy equipment which may
overstress any portion of a floor. All damages done to the Building by taking in
or putting out any property of Tenant, or done by Tenant's property while in the
Building, shall be repaired at the expense of Tenant, unless caused by
Landlord's gross negligence or willful misconduct.

7.   Corridor doors, when not in use, shall be kept closed.

8.   Tenant space visible from a public area must be kept neat and clean.

9.   Should Tenant require telegraphic, telephonic, annunciator, or other
communication services, Landlord will direct the electricians as to where and
how wires are to be introduced and placed, and none shall be introduced or
placed except as Landlord shall reasonably direct. Electric current shall not be
used for power or heating without Landlord's prior written permission, which
consent shall not be unreasonably withheld.

10.  No animals shall be brought into or kept in, on, or about the Building.

11.  Passenger elevators are to be used only for the movement of persons, unless
an exception is approved by the Building management office.
<PAGE>

12.  Tenant shall not tamper with or attempt to adjust temperature control
thermostats in the Premises. Landlord shall adjust thermostats as required to
maintain the Building standard temperature. Landlord requests that all window
blinds remain down and tilted at a 45 degree angle toward the street to help
maintain comfortable room temperatures and conserve energy.

13.  Tenant will comply with all reasonable security procedures provided to
Tenant in writing during business hours and after hours and on weekends.

14.  Tenants are requested to lock all office doors leading to corridors and to
turn out all lights at the close of their working day.

15.  All requests for overtime air conditioning or heating must be submitted in
writing to the Building management office by 4:00 p.m. on the preceding Business
Day.

16.  No flammable or explosive fluids or materials shall be kept or used within
the Building except in areas approved by Landlord, and Tenant shall comply with
all applicable building and fire codes relating thereto.

17.  Tenant may not place any items on the balconies of the Building without
obtaining Landlord's prior written consent.

18.  No smoking shall be permitted in the Premises. Smoking shall only be
permitted in the areas expressly designated by Landlord from time to time.

19.  Subject to the terms of the Lease, Landlord reserves the right to rescind
any of these rules and regulations and to make such other and further reasonable
and non-discriminatory rules and regulations as in its good faith judgment shall
from time to time be needed for the safety, protection, care and cleanliness of
the Property, the operation thereof, the preservation of good order therein, and
the protection and comfort of the tenants and their agents, employees, and
invitees, provided such rules and regulations do not materially increase
Tenant's obligations or liabilities under the Lease and which rules and
regulations, when made and written notice thereof is given to Tenant, shall be
binding upon Tenant in like manner as if originally herein prescribed.
<PAGE>

                                   EXHIBIT G

                            PROPOSED TENANT SIGNAGE
                            -----------------------

               [TO BE ATTACHED SUBSEQUENT TO LEASE SIGNING UPON
                   MUTUAL AGREEMENT OF LANDLORD AND TENANT]
<PAGE>

                                   EXHIBIT H

                            CLEANING SPECIFICATIONS
                            -----------------------
<PAGE>

                                   EXHIBIT I

                                 PARKING AREA
                                 ------------

               [TO BE ATTACHED SUBSEQUENT TO LEASE SIGNING UPON
                   MUTUAL AGREEMENT OF LANDLORD AND TENANT]<PAGE>

                                                                   EXHIBIT 10.34

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

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

                           STOCK PURCHASE AGREEMENT

                                BY AND BETWEEN

                     NETWORK ACCESS SOLUTIONS CORPORATION

                                      AND

                            SBC COMMUNICATIONS INC.

                               February 4, 2000
<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<S>                                                                                                <C>
Section 1: Defined Terms........................................................................    1

Section 2: Terms of Purchase and Sale...........................................................    7
       2.1   Conveyance of Stock................................................................    7
       2.2   Purchase Price for the Preferred Shares............................................    7
       2.3   Number of Preferred Shares to be Issued at the Closing.............................    7

Section 3: Closing..............................................................................    7
       3.1   The Closing........................................................................    7
       3.2   Deliveries by SBC..................................................................    8
       3.3   Deliveries by NAS..................................................................    8

Section 4: Conditions to NAS's Obligations......................................................    9
       4.1    Consents..........................................................................    9
       4.2    Litigation........................................................................    9
       4.3    SBC Representations; Compliance with Covenants....................................    9
       4.4    Deliveries........................................................................    9
       4.5    SBC Change in Control Event.......................................................   10
       4.6    Telmex Agreement..................................................................   10

Section 5: Conditions to SBC's Obligations......................................................   10
       5.1    Consents..........................................................................   10
       5.2    Litigation........................................................................   10
       5.3    NAS's Representations; Compliance with Covenants..................................   10
       5.4    NAS Change in Control Event.......................................................   11
       5.5    Adverse Developments..............................................................   11
       5.6    Deliveries........................................................................   11

Section 6: Representations and Warranties of SBC................................................   11
       6.1    Organization and Standing.........................................................   11
       6.2    Authorization by SBC..............................................................   11
       6.3    Litigation........................................................................   12
       6.4    Finders' and Brokers' Fees........................................................   12
       6.5    Investment Intent; Qualification..................................................   12
       6.6    Representations Not Misleading....................................................   12

Section 7: Representations and Warranties of NAS................................................   13
       7.1    Organization and Standing of NAS..................................................   13
</TABLE>

                                       i
<PAGE>

<TABLE>
<S>                                                                                                <C>
       7.2    Authorization by NAS; Consents....................................................   13
       7.3    Corporate Documents...............................................................   14
       7.4    Licenses; Qualification...........................................................   14
       7.5    Litigation........................................................................   14
       7.6    Exclusive Dealing.................................................................   15
       7.7    Compliance with Applicable Laws...................................................   15
       7.8    Title to Preferred Shares; Absence of Liens.......................................   15
       7.9    Financial Statements..............................................................   15
       7.10   Conduct of Business in Ordinary Course............................................   16
       7.11   No Material Adverse Effect........................................................   16
       7.12   Absence of Defaults...............................................................   16
       7.13   No Conflict.......................................................................   16
       7.14   Capital Stock of NAS..............................................................   17
       7.15   Finders' and Brokers' Fees........................................................   17
       7.16   Taxes.............................................................................   17
       7.17   Subsidiaries......................................................................   17
       7.18   Representations Not Misleading....................................................   17

Section 8: Covenants of SBC.....................................................................   18
       8.1    Cooperation.......................................................................   18
       8.2    Confidentiality; Press Releases...................................................   18
       8.3    Definitive Operating Agreement....................................................   18
       8.4    Consent Relating to Registration Rights...........................................   18
       8.5    Further Assurances................................................................   19

Section 9: Covenants of NAS.....................................................................   19
       9.1    Cooperation.......................................................................   19
       9.2    Access to NAS Information.........................................................   19
       9.3    Ordinary Course Operation.........................................................   19
       9.4    Board Representation..............................................................   19
       9.5    Confidentiality; Press Releases...................................................   20
       9.6    Notification of Change in Control Event...........................................   20
       9.7    Registration Rights...............................................................   20
       9.8    Listing...........................................................................   23
       9.9    Issuance of Other Securities......................................................   23
       9.10   Further Assurances................................................................   23
       9.11   Use of Proceeds...................................................................   23
       9.12   Definitive Operating Agreement....................................................   24
       9.13   Right of Primary Offer............................................................   24
       9.14   Government License Application Amendment..........................................   25

Section 10: Termination.........................................................................   25
       10.1   Terminating Events................................................................   25
</TABLE>

                                      ii
<PAGE>

<TABLE>
<S>                                                                                                <C>
       10.2   Effect on Obligations.............................................................   26

Section 11: Indemnification.....................................................................   26
       11.1   Indemnification by NAS............................................................   26
       11.2   Indemnification by SBC............................................................   27
       11.3   Losses............................................................................   27
       11.4   Survival..........................................................................   27
       11.5   Procedures Relating to Third Party Claims.........................................   28

Section 12: Arbitration.........................................................................   29
       12.1   Resolution of Disputes............................................................   29
       12.2   Arbitrators.......................................................................   30
       12.3   Costs and Fees....................................................................   30
       12.4   Burden of Proof...................................................................   30
       12.5   Award.............................................................................   30
       12.6   Agreement Controls................................................................   30

Section 13: Miscellaneous.......................................................................   31
       13.1   Entire Agreement; Amendment.......................................................   31
       13.2   Successors and Assigns............................................................   31
       13.3   Rights and Remedies...............................................................   31
       13.4   Counterparts......................................................................   31
       13.5   Modification and Waiver...........................................................   31
       13.6   Expenses..........................................................................   32
       13.7   Notices...........................................................................   32
       13.8   Severability......................................................................   33
       13.9   Governing Law.....................................................................   33
       13.10  Rules of Construction.............................................................   33
       13.11  Ownership Limitation..............................................................   34
</TABLE>

                                      iii
<PAGE>

Schedules:

       7.2    Consents Exceptions
       7.4    NAS Licenses
       7.5    Litigation
       7.6    Exclusive Dealing Exceptions
       7.8    Outstanding Options or Rights
       7.9    Financial Statements
       7.10   Ordinary Course Exceptions
       7.13   Conflicts
       7.14   NAS Capital Stock
       7.15   Finders' and Brokers' Fees
       7.17   Subsidiaries

Exhibits:

       A      Certificate of Designations
       B      Form of Shook, Hardy & Bacon Legal Opinion
       C      Summary of Operating Agreement

                                      iv
<PAGE>

                           STOCK PURCHASE AGREEMENT

     This Stock Purchase Agreement (the "Agreement"), dated as of February 4,
2000, is by and between SBC Communications Inc., a Delaware corporation ("SBC"),
and Network Access Solutions Corporation, a Delaware corporation ("NAS").

RECITALS
--------

     WHEREAS, SBC wishes to acquire, and NAS wishes to sell to SBC, shares of
preferred stock of NAS;

     NOW THEREFORE, in consideration of the mutual covenants contained herein,
SBC and NAS agree as follows:

Section 1:  Defined Terms
-------------------------

     The following terms shall have the following meanings in this Agreement:

     "AAA" means the American Arbitration Association.

     "Affiliate" means, with respect to a Person, any other Person directly or
indirectly controlling, controlled by or under common control with such Person.

     "Agreement" shall have the meaning set forth in the preamble hereto.

     "Assets" means the contracts, NAS Licenses, personal property, intellectual
property and real property, and all other assets, rights and properties,
tangible and intangible, of NAS and used or held for use in the NAS Business,
including (without limitation) cash, cash equivalents and accounts receivable.

     "Basis" means any past or present fact, situation, circumstance, status,
condition, activity, practice, plan, occurrence, event, incident, action,
failure to act or transaction that forms or could form the basis for any
specified consequences.

     "Beneficial Owner" means, with respect to any security, a Person that
Beneficially Owns such security.

     "Beneficially Own" means having the right to vote or dispose of, or
"beneficially own" as determined pursuant to Rule 13d-3 under the Exchange Act
as in effect on the date of this Agreement, including pursuant to any agreement,
arrangement or understanding.
<PAGE>

     "Business Day" means a day other than (i) a Saturday or Sunday or (ii) a
day on which banking institutions are authorized or required by law or executive
order to remain closed in the domicile of SBC or NAS.

     "Closing" means the consummation of the transactions contemplated by this
Agreement in accordance with the provisions of Section 2 and Section 3.

     "Closing Date" shall mean the date on which the Closing occurs.

     "Code" means the Internal Revenue Code of 1986, as amended, and the
regulations thereunder, or any subsequent legislative enactment thereof, as in
effect from time to time.

     "Common Stock" shall mean, collectively, the Common Stock of NAS.

     "Communications Act" means the Communications Act of 1934, 47 U.S.C.
Section 151 et seq., as amended and in effect from time to time.

     "Company Control Person" shall have the meaning set forth in Section 11.2.

     "Consents" means all of the consents, permits or approvals of Governmental
Authorities and other Persons necessary or required to consummate the
transactions contemplated hereby.

     "Control Person" shall have the meaning set forth in Section 11.1.

     "Convertible Securities" means any securities convertible into,
exchangeable for or bearing a right to acquire Common Stock.

     "Definitive Operating Agreement" means a mutually agreeable definitive
operating agreement(s) between NAS and SBC Telecom, Inc. as contemplated by, and
containing terms and conditions substantially as set forth in, the Summary of
Operating Agreement attached as Exhibit C hereto.

     "Dispute" shall have the meaning set forth in Section 12.1(a).

     "Dispute Notice" shall have the meaning set forth in Section 12.1(a).

     "Exchange Act" shall mean the Securities Exchange Act of 1934, as amended
and in effect from time to time.

     "Enforceability Exceptions" shall have the meaning set forth in Section
6.2(a).

     "FCC" means the Federal Communications Commission or any successor thereto.

     "FCC Rules" means Title 47 of the Code of Federal Regulations, as amended
at any time and from time to time, and FCC decisions issued pursuant to the
adoption of such regulations.

                                       2
<PAGE>

     "Final Order" means an order as to which the time for filing a request for
administrative or judicial relief, or for instituting administrative review sua
sponte, shall have expired without any such filing having been made or notice of
review having been issued; or, in the event of such filing or review sua sponte,
as to which such filing or review shall have been disposed of favorably to the
order and the time for seeking further relief with respect thereto shall have
expired without any request for such further relief having been filed.

     "Fully Diluted" shall mean, with respect to the number of Shares
outstanding on a fully diluted basis, the number of Shares which would be
outstanding at the time of determination assuming the conversion, exchange or
exercise of all Convertible Securities (irrespective of any legal or contractual
restriction on such exercise, exchange or conversion), and any reference herein
to the number of Shares outstanding shall mean the number of Shares outstanding
assuming no conversion, exchange or exercise of Convertible Securities.

     "GAAP" means generally accepted accounting principles consistent with the
past practices of NAS.

     "Governmental Authority" means (i) the United States, any state,
commonwealth, territory, or possession thereof and any political subdivision or
quasi-governmental authority of any of the same, including but not limited to
courts, tribunals, departments, commissions, boards, bureaus, agencies,
counties, municipalities, provinces, parishes, and other instrumentalities, and
(ii) any foreign (as to the United States) sovereign entity, including but not
limited to nations, states, republics, kingdoms and principalities, any
province, commonwealth, territory or possession thereof, and any political
subdivision, quasi-governmental authority, or instrumentality of any of the
same.

     "Holder" means SBC and each transferee of SBC's rights hereunder that is a
Wholly-Owned SBC Subsidiary and any other transferee of SBC's rights hereunder
to which NAS consents, which consent shall not be unreasonably withheld.

     "HSR Act" means the Hart-Scott-Rodino Antitrust Improvements Act of 1976,
as amended and in effect from time to time.

     "Indemnified Party" shall have the meaning set forth in Section 11.5.

     "IRS" shall mean the Internal Revenue Service and any governmental body or
agency succeeding to the functions thereof.

     "Judgment" means any judgment, writ, order, injunction, award or decree of
any court, judge, justice or magistrate, including any bankruptcy court, or
arbiter, and any order of or by any other Governmental Authority.

     "Knowledge" with respect to NAS means the actual knowledge of NAS and, with
respect to SBC, means the actual knowledge of SBC.

                                       3
<PAGE>

     "Legal Requirements" means applicable common law and any applicable
statute, ordinance, code or other law, rule, regulation, order, technical or
other standard, requirement or procedure enacted, adopted, promulgated or
applied by any Governmental Authority, including any Judgment.

     "Lien" means any security agreement, financing statement filed with any
Governmental Authority, conditional sale or other title retention agreement, any
lease, consignment or bailment given for the purpose of security, any lien,
mortgage, indenture, pledge, option, encumbrance, restriction on transfer,
adverse interest, constructive trust or other trust, claim, attachment,
exception to or defect in title or other ownership interest (including but not
limited to reservations, rights of entry, possibilities of reverter,
encroachments, easements, rights-of-way, restrictive covenants, leases and
licenses) of any kind, which otherwise constitutes an interest in or claim
against property, whether arising pursuant to any Legal Requirement, contract or
otherwise.

     "Litigation" means any claim, action, suit, proceeding, arbitration,
investigation, hearing or other activity or procedure that could result in a
Judgment, and any notice of any of the foregoing.

     "Losses" means any losses, liabilities, damages, Liens, penalties, costs,
fines and expenses, whether in connection with any Litigation or otherwise,
including but not limited to interest which may be imposed in connection
therewith, expenses of investigation, reasonable fees and disbursements of
counsel and other experts, and the cost to any Person making a claim or seeking
indemnification under this Agreement with respect to funds expended by such
Person by reason of the occurrence of any event with respect to which
indemnification is sought.

     "Material Adverse Effect" shall mean, with respect to either party, a
material adverse change in the financial condition or financial results of
operations of such party or the occurrence of any event or combination of events
that is reasonably likely to result in a material adverse change in the
financial condition or financial results of operations of such party and its
Subsidiaries taken as a whole. When the phrase "material adverse" is used in
this Agreement and is not used as a capitalized term and in the phrase "Material
Adverse Effect," such "material adverse" reference shall not be defined or
construed as provided in the immediately preceding sentence or in the context of
such party taken as a whole but instead shall mean a material adverse effect,
change or consequences only as to the matter with respect to which the phrase
"material adverse" is utilized.

     "NAS" shall have the meaning set forth in the preamble hereto.

     "NAS Business" means NAS's business as conducted  in the United States in
accordance with NAS's existing operations and business plans.

     "NAS Change in Control Event" shall be deemed to have occurred if (i) there
shall be consummated (x) any consolidation or merger of NAS in which NAS is not
the continuing or surviving corporation or pursuant to which shares of the
Common Stock would be converted into cash, securities or other property, other
than a merger of NAS in which the holders of the Common

                                       4
<PAGE>

Stock immediately prior to the merger have the same proportionate ownership of
common stock of the surviving corporation immediately after the merger, or (y)
any sale, lease, exchange or other transfer (in one transaction or a series of
related transactions) of all, or substantially all, of the Assets of NAS, or
(ii) the stockholders of NAS approved any plan or proposal for the liquidation
or dissolution of NAS, or (iii) any Person other than Jonathan P. Aust and
Spectrum Equity Investors II, L.P shall become the Beneficial Owner of 20% or
more of the outstanding Common Stock or (iv) during any period of two
consecutive years, individuals who at the beginning of such period constitute
the entire NAS Board of Directors shall cease for any reason to constitute a
majority thereof unless the election, or the nomination for election by NAS's
stockholders, of each new director was approved by a vote of at least two-thirds
of the directors then still in office who were directors at the beginning of the
period.

     "Nasdaq" means Nasdaq National Market.

     "NAS Financial Statements" shall mean (i) the consolidated balance sheets
(including related notes and schedules, if any) of NAS as of September 30, 1999
and as of December 31, 1998 and the related consolidated statements of income,
shareholders' equity and cash flows (including related notes and schedules, if
any) and (ii) the consolidated balance sheets of NAS (including related notes
and schedules, if any) and related statements of income, shareholders' equity
and cash flows (including related notes and schedules, if any) with respect to
periods ended subsequent to September 30, 1999.

     "NAS Licenses" means all Section 214 authorizations or microwave and other
spectrum licenses issued by the FCC, and all certificates of public convenience
and necessity or comparable authorizations issued by any state public utilities
commission or comparable regulatory authority, and held by NAS.

     "New Securities" shall have the meaning set forth in Section 9.13(d)(i).

     "Note" shall mean that certain Promissory Note dated of even date herewith,
in the original principal amount of $15,000,000.00, payable by NAS to SBC.

     "Notice" shall have the meaning set forth in Section 9.13(a).

     "Outstanding" with respect to the number of Shares outstanding on a fully
diluted basis, shall have the meaning set forth in the definition of the term,
"Fully Diluted."

     "Percentage" shall have the meaning set forth in Section 9.13(d)(ii).

     "Permitted Registration Date" means the date that is the later of (i) two
years from the Closing Date, or (ii) the date of termination of the Definitive
Operating Agreement.

     "Person" means any natural person, Governmental Authority, corporation,
general or limited partnership, limited liability company, limited liability
partnership, joint venture, trust, estate, association, organization or
unincorporated entity of any kind.

                                       5
<PAGE>

     "Preferred Shares" means the Convertible Series B Preferred Stock of NAS,
as the terms of such Preferred Shares are set forth in the Certificate of
Designations attached as Exhibit A hereto.

     "Prior Holders" shall have the meaning set forth in Section 9.7.

     "Purchase Price" means $75,000,000.00.

     "Registration Request" shall have the meaning set forth in Section 9.7(b).

     "Registration Statement" shall have the meaning set forth in Section
9.7(b).

     "SBC" shall have the meaning set forth in the preamble hereto.

     "SEC" shall mean the Securities and Exchange Commission and any
governmental body or agency succeeding to the functions thereof.

     "SBC Change in Control Event" shall be deemed to have occurred if (i) there
shall be consummated (x) any consolidation or merger of SBC in which SBC is not
the continuing or surviving corporation or pursuant to which shares of the
Common Stock would be converted into cash, securities or other property, other
than a merger of SBC in which the holders of the Common Stock immediately prior
to the merger have the same proportionate ownership of common stock of the
surviving corporation immediately after the merger, or (y) any sale, lease,
exchange or other transfer (in one transaction or a series of related
transactions) of all, or substantially all, of the Assets of SBC, or (ii) the
stockholders of SBC approved any plan or proposal for the liquidation or
dissolution of SBC, or (iii) any Person shall become the Beneficial Owner of 20%
or more of the outstanding Common Stock or (iv) during any period of two
consecutive years, individuals who at the beginning of such period constitute
the entire SBC Board of Directors shall cease for any reason to constitute a
majority thereof unless the election, or the nomination for election by SBC's
stockholders, of each new director was approved by a vote of at least two-thirds
of the directors then still in office who were directors at the beginning of the
period.

     "Securities Act" shall mean the Securities Act of 1933, as amended and in
effect from time to time.

     "Selling Shareholder" shall have the meaning set forth in Section 9.7(b).

     "Subsidiary" of any corporation shall mean any other corporation, limited
liability company, general or limited partnership, limited liability
partnership, joint venture, trust or other entity of which the outstanding
capital stock possessing a majority of voting power in the election of directors
(otherwise than as the result of a default) is owned or controlled by such
corporation directly or indirectly through Subsidiaries.

     "Taxes" means all levies and assessments of any kind or nature imposed on
NAS by any Governmental Authority, including but not limited to all income,
sales, use, ad valorem, value added, franchise, severance, net or gross
proceeds, withholding, payroll, employment, excise or

                                       6
<PAGE>

property taxes, together with any interest thereon and any penalties, additions
to tax or additional amounts applicable thereto.

     "Telmex" shall mean Telefonos de Mexico, S.A. de C.V.

     "Third Party Claim" shall have the meaning set forth in Section 11.5.

     "Wholly-Owned SBC Subsidiary" means any corporation, limited liability
company, general or limited partnership, limited liability partnership, joint
venture, trust or other entity of which the outstanding capital stock is wholly
owned directly or indirectly by SBC and which is formed for business purposes
that are unrelated to the ability of such entity to receive any rights or
interests hereunder or associated herewith.

Section 2:  Terms of Purchase and Sale
--------------------------------------

2.1  Conveyance of Stock

     Subject to the terms and conditions of this Agreement, NAS shall issue to
SBC, free and clear of all Liens, the number of shares of its newly issued
Convertible Preferred Stock set forth in Section 2.3 (the "Preferred Shares").

2.2  Purchase Price for the Preferred Shares

     The aggregate purchase price for the Preferred Shares ("Purchase Price")
shall be $75,000,000.00.

2.3  Number of Preferred Shares to be Issued at the Closing

     The number of shares of Preferred Shares to be acquired by SBC at the
Closing shall be 750,000.

Section 3:  Closing
-------------------

3.1  The Closing

     Upon the terms and subject to the conditions contained herein (each party
agreeing to notify the other when all closing conditions have occurred), the
Closing shall take place at the offices of Arnold & Porter in Washington, D.C.,
at 2:00 p.m. local time on the date (the "Closing Date") which is five (5)
Business Days after each of the conditions set forth in Section 4 and 5 hereof
have been satisfied or waived, or any other mutually agreed upon time.

                                       7
<PAGE>

3.2  Deliveries by SBC

     On the Closing Date, SBC shall deliver or cause to be delivered to NAS the
following, in form and substance reasonably satisfactory to NAS and its counsel:

     (a)  The Purchase Price, (i) by wire transfer in the form of immediately
          available funds to an account designated by NAS and (ii) to the extent
          of the amount of unpaid principal and accrued interest on the Note, by
          tender of the Note;

     (b)  The Note, marked "Paid and Cancelled";

     (c)  A certificate, dated as of the Closing Date, executed by a Senior Vice
          President of SBC, certifying that the conditions set forth in Section
          4 have been fulfilled;

     (d)  A certificate, dated as of the Closing Date, executed by SBC's
          Secretary certifying that the execution of this Agreement and the
          consummation of the transaction contemplated hereby have been
          authorized and approved by all necessary corporate action of SBC,
          which remains in full force and effect and has not been modified or
          amended; and

     (e)  Such other documents and instruments as shall be reasonably necessary
          to effect the intent of this Agreement and consummate the transactions
          contemplated by this Agreement.

3.3  Deliveries by NAS

     On the Closing Date, NAS shall deliver to SBC the following, in form and
substance reasonably satisfactory to SBC and its counsel:

     (a)  A certificate or certificates for all of the Preferred Shares;

     (b)  A certificate, dated as of the Closing Date, executed by the President
of NAS, certifying that all the conditions set forth in Section 5 have been
fulfilled;

     (c)  A certificate, dated as of the Closing Date, executed by the Secretary
of NAS, certifying that the resolutions, as attached to such certificate, were
duly adopted by the Board of Directors of NAS authorizing and approving the
execution of this Agreement and the consummation of the transactions
contemplated hereby, and that such resolutions remain in full force and effect
and have not been modified or amended;

     (d)  SBC shall have been furnished with a favorable opinion, dated the
Closing Date; of outside counsel to NAS (which counsel shall be reasonably
satisfactory to SBC), confirming the matters set forth in Sections 7.1, 7.2 (as
to all transaction documents), 7.5, 7.8, 7.13, 7.14, and exemption of the
issuance and sale of the Series B Preferred Stock from the registration

                                       8
<PAGE>

requirements of the federal and state securities laws, which opinion shall be in
form and substance reasonably satisfactory to SBC.

     (e)  Opinions of Shook, Hardy & Bacon, NAS's state regulatory counsel,
dated as of the Closing Date, substantially in the form of Exhibit B hereto; and

     (f)  Such other documents and instruments as shall be reasonably necessary
to effect the intent of this Agreement and consummate the transactions
contemplated by this Agreement.

Section 4:  Conditions to NAS's Obligations
-------------------------------------------

     The obligations of NAS to sell the Preferred Shares and effect the Closing
shall be subject to the satisfaction by SBC, or waiver thereof by NAS, on or
prior to the Closing Date of all of the following conditions:

4.1  Consents

     All Consents shall have been obtained.

4.2  Litigation

     No Litigation shall be pending, and no Legal Requirement shall have been
enacted, entered, promulgated or issued, or shall have become or be deemed
applicable, to any of the transactions contemplated by this Agreement by any
Governmental Authority, that would (i) prohibit SBC's ownership of the Stock or
prohibit NAS's operation of the NAS Business in any material respect as it is
being operated as of the date of this Agreement, (ii) prevent or make illegal
the consummation of the transactions contemplated by this Agreement.

4.3  SBC Representations; Compliance with Covenants

     SBC's representations and warranties contained in Section 6 shall be
accurate in all material respects when made and at and as of the Closing with
the same effect as though such representations and warranties had been made at
and as of the Closing, and SBC shall have in all material respects performed and
complied with all covenants and agreements and conditions required by this
Agreement to be performed or complied with by it prior to or on the Closing,
provided that this condition shall be satisfied if the inaccuracy of any
representation or warranty, or the nonperformance or noncompliance with any
covenant, agreement or condition, individually or in the aggregate, does not
have a Material Adverse Effect.

4.4  Deliveries

     SBC shall have made or stand willing and able to make all of the deliveries
to NAS set forth in Section 3.2.

                                       9
<PAGE>

4.5  SBC Change in Control Event

     No SBC Change in Control Event shall have occurred.

4.6  Telmex Agreement

     Telmex shall have executed a stock purchase agreement with respect to the
purchase of 750,000 Preferred Shares in the form of this Agreement except for
appropriate changes to reflect Telmex as a party thereto.

Section 5:  Conditions to SBC's Obligations
-------------------------------------------

     The obligations of SBC to purchase the Preferred Shares and effect the
Closing shall be subject to the satisfaction, or waiver by SBC, on or prior to
the Closing Date of all of the following conditions:

5.1  Consents

     All Consents shall have been obtained.

5.2  Litigation

     No Litigation shall be pending, and no Legal Requirement shall have been
enacted, entered, promulgated or issued, or shall have become or be deemed
applicable, to any of the transactions contemplated by this Agreement by any
Governmental Authority, that would (i) prohibit SBC's ownership of the Preferred
Shares or prohibit NAS's operation of the NAS Business in any material respect
as it is being operated as of the date of this Agreement, or (ii) prevent or
make illegal the consummation of the transactions contemplated by this
Agreement.

5.3  NAS's Representations; Compliance with Covenants

     NAS's representations and warranties contained in Section 7 shall be
accurate in all respects when made and at and as of the Closing with the same
effect as though such representations and warranties had been made at and as of
the Closing except: (i) insofar as any such representation or warranty is made
specifically as of the date of this Agreement or as of any other specified
earlier date (in which event the same shall continue at and as of the Closing
Date to be true and correct as of such earlier date) and (ii) with respect to
changes contemplated by this Agreement, and NAS shall have in all material
respects performed and complied with all covenants and agreements and conditions
required by this Agreement to be performed or complied with by it prior to or on
the Closing Date, provided that this condition shall be satisfied if the
inaccuracy of any representation or warranty, or the nonperformance or
noncompliance with any covenant, agreement or condition, individually or in the
aggregate, does not have a Material Adverse Effect.

                                       10
<PAGE>

5.4  NAS Change in Control Event

     No NAS Change in Control Event shall have occurred.

5.5  Adverse Developments

     Since September 30, 1999, there shall not have occurred any change, or any
development involving a prospective change, in or affecting the business,
operations, properties, Assets or prospects of NAS which materially impairs the
value of the Preferred Shares.

5.6  Deliveries

     NAS shall have made or stand willing and able to make all of the deliveries
to SBC set forth in Section 3.3.

Section 6:  Representations and Warranties of SBC
-------------------------------------------------

     SBC hereby represents and warrants to NAS as follows:

6.1  Organization and Standing

     SBC is a corporation duly organized, validly existing and in good standing
under the laws of the State of Delaware and has all requisite corporate power
and authority to execute and deliver this Agreement and to perform its
obligations hereunder.

6.2  Authorization by SBC

     (a)  This Agreement has been duly and validly executed and delivered by SBC
and constitutes the legal, valid and binding obligation of SBC enforceable
against SBC in accordance with its terms, except as such enforceability may be
limited by (i) bankruptcy, insolvency, or other similar laws affecting the
enforcement of creditors' rights generally or (ii) general principles of equity
(collectively, the "Enforceability Exceptions").

     (b)  Neither the execution, delivery and performance of this Agreement by
SBC nor the consummation by SBC of the transactions contemplated herein will,
with or without the giving of notice or the lapse of time, or both, (i) violate
any Legal Requirements to which SBC is subject, (ii) conflict with or result in
a breach of the terms, conditions or provisions of, or constitute a default
under, the charter or by-laws of SBC or any material agreement or commitment to
which SBC is a party or by which SBC or any of SBC's assets, may be bound or
affected, or (iii) require SBC to obtain any authorization, consent, approval or
waiver from, or to make any filing with, any Governmental Authority or non-
governmental third party. NAS has informed SBC that the approvals referred to on
Schedule 7.2 are required for consummation of the transactions contemplated by
this Agreement.

                                       11
<PAGE>

6.3  Litigation

     There is no Litigation pending against SBC or, to the best of SBC's
Knowledge, any Basis for Litigation or threatened Litigation against SBC which
seeks to enjoin or obtain damages in respect of the consummation of the
transactions contemplated hereby. SBC is not a party to or involved in any
Litigation which has a material adverse effect on SBC's ability to consummate,
or would prevent the consummation of, the transactions contemplated by this
Agreement.

6.4  Finders' and Brokers' Fees

     Neither SBC, nor anyone on behalf of SBC, has any obligations to any
broker, finder or agent, or agreed to pay any brokerage fee, finder's fee or
commission in connection with this Agreement or the transactions contemplated
hereby.

6.5  Investment Intent; Qualification

     (a)  SBC is acquiring the Preferred Shares solely for its own account, for
investment purposes only, and not with a view to any distribution thereof, in
whole or in part, within the meaning of the Securities Act or any applicable
state securities laws. The Preferred Shares will not be resold by SBC unless
registered pursuant to the Securities Act and any applicable state securities
laws or unless an exemption therefrom is available. SBC hereby acknowledges that
NAS will rely upon the truth of the representations made in this Section 6.5 in
determining that an exemption from the registration requirements of the
securities laws is available in connection with the sale of the Preferred Shares
pursuant to this Agreement.

     (b)  SBC has the ability to evaluate the merits and risks associated with
its investment in the Preferred Shares on the basis of SBC's knowledge and
experience in financial and business matters. SBC is an "accredited investor" as
defined in Rule 501 of the General Rules and Regulations under the Securities
Act. SBC has not relied upon any representation or warranty made by NAS, or by
any person on behalf of NAS, other than the representations and warranties
contained in this Agreement.

6.6  Representations Not Misleading

     The representations made by SBC in this Agreement do not contain any untrue
statement of a material fact or omit to state a material fact necessary in order
to make the statements therein, in light of the circumstances under which they
were made, not misleading.

                                       12
<PAGE>

Section 7:  Representations and Warranties of NAS
-------------------------------------------------

     NAS hereby represents and warrants to SBC as follows:

7.1  Organization and Standing of NAS

     NAS is a corporation duly organized, validly existing and in good standing
under the laws of the State of Delaware with all requisite power and authority
(corporate and other) to own its properties and conduct its business as now
being conducted, and is duly qualified to do business as a foreign corporation
in good standing in each jurisdiction where the ownership of its properties or
the conduct of its business makes such qualification necessary, except in those
jurisdictions where failure so to qualify will not permanently impair title to a
material amount of its properties or its rights to enforce in all material
respects contracts against others or expose it to substantial liabilities in
such jurisdictions. Each Subsidiary of NAS is a corporation duly organized,
validly existing and in good standing under the laws of its state of
incorporation with all requisite power and authority (corporate and other) to
own its properties and conduct its business as now being conducted, and is duly
qualified to do business as a foreign corporation in good standing in each
jurisdiction where the ownership of its properties or the conduct of its
business makes such qualification necessary, except in those jurisdictions where
failure so to qualify will not permanently impair title to a material amount of
its properties or its rights to enforce in all material respects contracts
against others or expose it to substantial liabilities in such jurisdictions.

7.2  Authorization by NAS; Consents

     (a)  NAS has all requisite corporate power and authority to execute,
deliver and perform its obligations under this Agreement. NAS has taken all
corporate action necessary to authorize this Agreement and the issue, sale and
delivery of the Preferred Shares. This Agreement has been duly authorized,
executed and delivered by NAS and is a legal, valid and binding obligation of
NAS enforceable in accordance with its terms, except as such enforceability may
be limited by the Enforceability Exceptions.

     (b)  All material Consents required to be obtained by NAS are set forth on
Schedule 7.2. Except for the Consents set forth in Schedule 7.2, neither the
execution, delivery and performance of this Agreement by NAS nor the
consummation by NAS of the transactions contemplated herein will, with or
without the giving of notice or the lapse of time, or both, (i) violate any
Legal Requirements to which NAS is subject, (ii) conflict with or result in a
breach of the terms, conditions or provisions of, or constitute a default under,
the charter or by-laws of NAS, or any NAS License, any material contract to
which NAS is a party or by which NAS may be bound or affected, or (iii) require
NAS to obtain any authorization, consent, approval or waiver from, or to make
any filing with, any Governmental Authority or non-governmental third party.

                                       13
<PAGE>

7.3  Corporate Documents

     True and correct copies of the Amended and Restated Certificate of
Incorporation and the Amended and Restated By-Laws of NAS, certified by an
appropriate officer of NAS, have been delivered to SBC and such Amended and
Restated Certificate of Incorporation, as amended, and Amended and Restated By-
Laws have not been amended since the respective dates of certification thereof,
nor has the Board of Directors or the shareholders of NAS taken any action for
the purpose of effecting the amendment or modification of such Amended and
Restated Certificate of Incorporation or Amended and Restated By-Laws.

7.4  Licenses; Qualification

     (a)  NAS or its Subsidiaries hold all the NAS Licenses listed in Schedule
7.4 hereto in its corporate name. The NAS Licenses listed in Schedule 7.4 are
all of the material and necessary Licenses which are required in connection with
the current operation of the NAS Business. Except as set forth on Schedule 7.4,
all NAS Licenses are currently in full force and effect and there are no pending
or, to the Knowledge of NAS, threatened revocation proceedings which would have
a Material Adverse Effect on the operation of the NAS Business, nor, to the
Knowledge of NAS, is there any Basis for any such proceeding. NAS has made
available to SBC for SBC's review, accurate and complete copies of all NAS
Licenses.

     (b)  All fees due and payable to Governmental Authorities pursuant to the
NAS Licenses have been paid and, except as set forth on Schedule 7.4, no event
has occurred which, with or without the giving of notice or the lapse of time or
both, would constitute grounds for revocation of the NAS Licenses. Except as set
forth on Schedule 7.4, NAS is in compliance in all material respects with the
terms of the NAS Licenses, and there is no condition, event or occurrence
existing, nor is there any proceeding being conducted of which NAS has received
notice, nor, to NAS's Knowledge, is there any proceeding threatened, by any
Governmental Authority, which would cause the termination, suspension,
cancellation or nonrenewal of any of the NAS Licenses, or the imposition of any
material penalty or fine by any Governmental Authority, nor, to the Knowledge of
NAS, is there any Basis for any such proceeding.

     (c)  Except as set forth on Schedule 7.4, to NAS's Knowledge, all
applications, reports, fees, filings and other submissions required by any
Governmental Authority have been made or paid in a timely fashion, the
noncompliance with which reasonably could have a Material Adverse Effect.

7.5  Litigation

     There is no Litigation pending against NAS or any of its Subsidiaries, or,
to the Knowledge of NAS, a Basis for Litigation or threatened Litigation against
NAS or any of its Subsidiaries which seeks to enjoin or obtain damages in
respect of the consummation of the transactions contemplated hereby.  Except for
those matters disclosed on Schedule 7.5, as of the date hereof there is no
Litigation or, to the Knowledge of NAS, Basis for Litigation, against NAS or any
of its Subsidiaries (including proceedings concerning labor disputes or
grievances, civil

                                       14
<PAGE>

rights discrimination cases and affirmative action proceedings) nor is there any
governmental investigation pending or, to NAS's Knowledge, Basis for
governmental investigation or threatened governmental investigation relating to
NAS or any of its Subsidiaries or to which NAS or any such Subsidiary is a
party, nor is there any Judgment relating to NAS or any of its Subsidiaries or
to which NAS or any of its Subsidiaries is a party which is unsatisfied or
requires continuing compliance. Neither NAS nor any of its Subsidiaries is a
party to or involved in any Litigation which has a Material Adverse Effect upon
NAS's ability to consummate, or would prevent the consummation of, the
transactions contemplated by this Agreement.

7.6  Exclusive Dealing

     Except as set forth on Schedule 7.6, neither NAS nor any of its Affiliates
is a party to any currently effective agreement, written or oral, involving the
sale of any NAS Securities, a material portion of NAS's Assets, or any of the
NAS Business to any Person other than SBC and Telmex.

7.7  Compliance with Applicable Laws

     NAS and each of its Subsidiaries has complied and presently is in
compliance with all applicable Legal Requirements.

7.8  Title to Preferred Shares; Absence of Liens

     (a)  The Preferred Shares have been duly authorized for issuance and are
validly issued, fully paid and nonassessable. None of the Preferred Shares has
been issued in violation of, or is subject to, any preemptive or subscription or
similar rights. Except as disclosed on Schedule 7.8 there are no outstanding
options or rights of any kind to acquire or subscribe for any Preferred Shares
nor are there any obligations to issue, sell or otherwise cause to become
outstanding any such options, rights, capital stock or securities. Except as
disclosed on Schedule 7.8, NAS is not a party to, and does not have any
Knowledge of, any voting trusts, proxies, voting agreements or other agreements
with respect to the voting of the capital stock of NAS.

     (b)  SBC will acquire at the Closing good title to the Preferred Shares,
free and clear of all Liens.

     (c)  NAS owns all of the issued and outstanding capital stock of each of
its Subsidiaries.

7.9  Financial Statements

     Attached as Schedule 7.9 are the unaudited NAS Financial Statements for
September 30, 1999 in the form included in NAS's Form 10-Q for the nine months
ended September 30, 1999. The NAS Financial Statements have been prepared by NAS
in accordance with GAAP and present fairly the financial position of NAS and its
Subsidiaries as of the dates of such

                                       15
<PAGE>

statements. There are no material
contingent liabilities that are not disclosed on the NAS Financial Statements.

7.10  Conduct of Business in Ordinary Course

      Since September 30, 1999, and except as set forth on Schedule 7.10, NAS
has conducted the NAS Business only in the ordinary course and consistent with
past practices and has not: (i) made any material increase in compensation
payable or to become payable to any senior executives of NAS, or any material
change in personnel policies, insurance benefits or other compensation
arrangements affecting NAS's employees; (ii) made any sale, assignment, lease or
other transfer of any of the Assets, other than obsolete Assets no longer usable
in the operation of the NAS Business or other Assets sold or disposed of in the
normal course of business with suitable replacements being obtained therefor;
(iii) experienced any physical damages, destruction or loss exceeding $50,000.00
in the aggregate affecting the NAS Business that is not covered by insurance or
has not been remedied within 30 days; (iv) incurred any indebtedness or Liens
except in the ordinary course and consistent with past practices; (v) paid any
dividends; or (vi) waived any material rights of NAS under any contract or NAS
License.

7.11  No Material Adverse Effect

      Since September 30, 1999, there has been no Material Adverse Effect.

7.12  Absence of Defaults

      Neither NAS nor any of its Subsidiaries is in material default under or in
material violation of any provision of its Amended and Restated Certificate of
Incorporation or Amended and Restated By-Laws or contained in any other
agreement or instrument to which it is a party or by which it is bound or to
which any of its properties is subject, and neither NAS nor any of its
Subsidiaries is in material violation of any statute, order, rule or regulation
of any court or governmental agency or body having jurisdiction over it or any
of its properties.

7.13  No Conflict

      Except as set forth on Schedule 7.13, neither the execution and delivery
by NAS of this Agreement, nor the consummation of the transactions contemplated
hereby, nor compliance by NAS with its obligations hereunder:

           (i)   will conflict with, or result in a breach or violation of, or
      constitute a default under, any provision of the Amended and Restated
      Certificate of Incorporation or Amended and Restated By-Laws of NAS or any
      law, rule, regulation, order, injunction or decree of any court,
      administrative authority or arbitrator applicable to NAS or any property
      or Assets of NAS, or will conflict with, or result in a breach or
      violation of or constitute a default in the performance, observance or
      fulfillment of any obligation under, or constitute, or, with the giving of
      notice or lapse of time or both, would constitute, an event of default by
      NAS, or result in the acceleration of any obligation, or require any

                                       16
<PAGE>

      consent or approval, under, any agreement or instrument to which NAS is a
      party or by which it or any of its properties or Assets are bound;

           (ii)   will result in the creation or imposition of any Lien upon any
      of the Assets of NAS; or

           (iii)  will require any action, consent or approval of, or filing
      with, any Governmental Authority.

7.14  Capital Stock of NAS

      The authorized capital stock of NAS as of the date hereof is as set forth
on Schedule 7.14 and no other shares are issued or outstanding, except as a
result of the expiration of employee options on February 4, 2000. Each issued
and outstanding share of Common Stock is duly and validly authorized and issued
and is fully paid and nonassessable. The Preferred Shares, when issued and
delivered to SBC pursuant to this Agreement will be duly and validly authorized
and issued and fully paid and nonassessable. There is no existing option,
warrant, call or commitment of any kind relating to the capital stock of NAS or
securities convertible into capital stock of NAS except as set forth on Schedule
7.14. The Preferred Shares are not and will not at the time of issuance be
subject to any preemptive right of any shareholder.

7.15  Finders' and Brokers' Fees

      Neither NAS, nor anyone on behalf of NAS, has any obligations to any
broker, finder or agent, or agreed to pay any brokerage fee, finder's fee or
commission in connection with this Agreement and the transactions contemplated
hereby except as set forth on Schedule 7.15.

7.16  Taxes

      NAS and each of its Subsidiaries has filed or caused to be filed all
federal, state and local tax returns which are required to be filed by it, and
has paid or caused to be paid all taxes shown to be due and payable on such
returns or on any assessments received by it, including payroll taxes.

7.17  Subsidiaries

      Other than as set forth on Schedule 7.17 hereto, NAS has no Subsidiaries.

7.18  Representations Not Misleading

      The representations made by NAS in this Agreement do not contain any
untrue statement of a material fact or omit to state a material fact necessary
in order to make the statements therein, in light of the circumstances under
which they were made, not misleading.

                                       17
<PAGE>

Section 8:  Covenants of SBC
----------------------------

     SBC hereby covenants and agrees with NAS as follows:

8.1  Cooperation

     SBC will use commercially reasonable efforts and cooperate with NAS to
secure promptly all necessary Consents.

     SBC will not sell or otherwise dispose of any Preferred Shares except in
compliance with the provisions of the Securities Act, the SEC's regulations
thereunder and other applicable federal and state securities and Blue Sky laws.

8.2  Confidentiality; Press Releases

     No press release or public disclosure, either written or oral, of the
existence or terms of this Agreement shall be made by SBC without the consent of
NAS, and SBC shall furnish to NAS advance copies of any release which it
proposes to make public concerning this Agreement or the transactions
contemplated hereby and the date upon which SBC proposes to make such press
release. This provision shall not, however, be construed to prohibit SBC from
making any disclosures to any Governmental Authority or other Person which it is
required to make under any Legal Requirement, or to obtain any Consents.

8.3  Definitive Operating Agreement

     Promptly following the execution of this Agreement, SBC shall, and shall
cause SBC Telecom, Inc. to, negotiate in good faith the Definitive Operating
Agreement. The Definitive Operating Agreement shall contain the substance of the
terms and conditions set forth in the Summary of Operating Agreement attached as
Exhibit C and such other terms and conditions as the parties may mutually agree
upon.

8.4  Consent Relating to Registration Rights

     Upon receipt by NAS of the consents of the Prior Holders referred to in
Section 9.7, SBC (and any Holder) also will consent (i) to permit each Prior
Holder to participate in any registration statement in which the Holders may
participate and (ii) to the extent not all shares to be offered by the Holders
and Prior Holders may be sold under any such registration statement, to reduce
the number of shares the Holders, as a group, may sell under such registration
statement on a pro rata basis with the Prior Holders as a group, with such pro
rata reduction based on the number of shares of Common Stock, or the shares of
Common Stock represented by Convertible Securities, that each group owns or
Beneficially Owns at the time of the relevant Registration Request.

                                       18
<PAGE>

8.5  Further Assurances

     At any time or from time to time after the Closing Date, SBC shall execute
and deliver any further instruments or documents, and take all such further
action as NAS may reasonably request, in order to effect this Agreement and
issue and deliver the Preferred Shares to SBC free and clear of all Liens.

Section 9:  Covenants of NAS
----------------------------

     NAS hereby covenants and agrees with SBC as follows:

9.1  Cooperation

     NAS will use commercially reasonable efforts and cooperate with SBC to
secure promptly all necessary Consents.

9.2  Access to NAS Information

     During the period prior to Closing, NAS will grant to SBC and its
representatives reasonable access to all the premises, books, records,
inventory, and physical plant relating to NAS. NAS shall cause its
representatives and independent auditors to furnish to SBC such financial and
other data and information with respect to NAS as SBC and/or its independent
accountants and counsel shall reasonably request, to the extent already in
existence and permitted by law.

9.3  Ordinary Course Operation

     Between the date of the Agreement and the Closing, NAS (i) shall, in all
material respects, operate the NAS Business, serve its customers, and preserve
and maintain the Assets of NAS and relationships with customers, vendors and
employees in a reasonable and prudent manner and (ii) shall, in all material
respects, conduct the NAS Business in the ordinary course. Through the Closing
Date, NAS will use its best efforts to maintain the current status of the NAS
Licenses.

9.4  Board Representation

     NAS shall ensure that SBC, as long as SBC owns all of the Preferred Shares
issued upon Closing or all of the Common Stock issued upon conversion of such
Preferred Shares (or owns a greater number of Preferred Shares or shares of
Common Stock than originally issued upon Closing or conversion), shall have the
right to elect its designated nominee as a member of the Board of Directors of
NAS. Until conversion of Preferred Shares to Common Stock, such member shall be
a nonvoting member; thereafter, the member shall be a full voting member of the
Board of Directors.

                                       19
<PAGE>

9.5  Confidentiality; Press Releases

     No press release or public disclosure, either written or oral, of the
existence or terms of this Agreement shall be made by NAS without the consent of
SBC, and NAS shall furnish to SBC advance copies of any release which it
proposes to make public concerning this Agreement or the transactions
contemplated hereby and the date upon which NAS proposes to make such press
release. This provision shall not, however, be construed to prohibit NAS from
making any disclosures to any Governmental Authority or other Person which it is
required to make under any Legal Requirement, or to obtain any Consents.

9.6  Notification of Change in Control Event

     NAS shall promptly notify SBC upon the occurrence of any NAS Change in
Control Event.

9.7  Registration Rights

     (a)  The registration rights in this Section 9.7 as they apply to the
Holders, Telmex and the stockholders of NAS who have, as of the date of this
Agreement, registration rights as to their stock in NAS (the "Prior Holders")
are subject to that certain letter agreement of even date among SBC, Telmex and
the Prior Holders.

     (b)  After the Permitted Registration Date, any Holder holding, in the
aggregate, at least 500,000 shares of Common Stock issued upon the conversion of
the Preferred Shares, shall have the right, on one occasion only, by written
request (a "Registration Request") of one or more Holders (the "Selling
Shareholders") to NAS, to require NAS to prepare a registration statement (the
"Registration Statement") on the appropriate form under the Securities Act with
respect to the Common Stock then owned by such Selling Shareholders for use in
connection with an underwritten public distribution of all or part of the
Subject Stock.

     (c)  If at any time after the Permitted Registration Date, NAS shall
propose to prepare on its own behalf or on behalf of any holders of any of its
Common Stock a registration statement in connection with an underwritten public
offering of any such shares of Common Stock, NAS shall give each Holder written
notice at least twenty or, in case of a registration statement proposed to be
filed pursuant to Rule 415 of the Securities Act, ten Business Days before the
anticipated filing date of such registration statement. Should any Holder
desire to have any shares of Common Stock included in such registration
statement, such Holder shall so notify NAS in writing (which notice, and the
notice of all other Holders with respect to such registration statement, shall
be deemed to be a Registration Request) no later than ten or, in the case of a
registration statement proposed to be filed pursuant to Rule 415 of the
Securities Act, five Business Days after NAS's notice is given, setting forth
the number of shares of Common Stock which such Holder requests to be included
in the registration statement and providing any other information requested by
NAS in its original notice relating to inclusion in the registration statement.
Any such registration statement that includes shares of Common Stock owned by
any Holder is hereinafter included in the term "Registration Statement" and each
Holder who owns

                                       20
<PAGE>

shares of Common Stock included in a Registration Statement shall be a Selling
Shareholder with respect to such Registration Statement.

     (d)  NAS may refuse to include in any such Registration Statement the
Common Stock owned by a Holder if in NAS's reasonable judgment, based on advice
of its investment bankers, inclusion of such shares of Common Stock would have
an adverse effect on the ability of NAS to complete such underwritten public
offering. If in accordance with a Registration Request pursuant to Section
9.7(b), NAS reduces the number of shares to be included in any such Registration
Statement in accordance with the foregoing, NAS will include in such
registration, to the extent of the number which NAS is so advised can be sold in
such offering, first, shares of Common Stock requested to be included in such
registration by the Selling Shareholders (subject to the rights, if any, of
Prior Holders) and, second, securities NAS proposes to sell and other securities
of NAS included in such registration by the holders thereof. If, as a result of
this Section 9.7(d) or as a result of the participation of Prior Holders in the
Registration Statement, the Selling Shareholders are not able to register all of
their shares of Common Stock requested to be registered pursuant to Section
9.7(b), such Registration Request will not be deemed to be the single allowable
Registration Request for purposes of Section 9.7(b) and the Holders' rights to
one additional Registration Request will be restored, and if as a result of such
reduction the Selling Shareholder is left with fewer than 500,000 shares of
Common Stock, then the 500,000 share limit in Section 7(b) shall not apply.

     (e)  With respect to any Registration Statement under this Section 9.7, NAS
will:

          (i)   prepare and file with the SEC the Registration Statement within
     120 days after a Selling Shareholders' notice requesting registration or
     inclusion in a proposed registration, and use its reasonable efforts to
     cause the securities covered by such Registration Statement to become
     registered and such Registration Statement to be declared effective as
     expeditiously as possible under the Securities Act or other applicable
     federal law and regulations (and cause to be prepared and file any
     amendments or supplements thereto as may be necessary to comply with
     applicable federal law and regulations); provided, however, that NAS may be
     allowed to defer filing of the Registration Statement: (A) if the Vice
     President - Legal of NAS reasonably determines in good faith that it is in
     the best interests of NAS not to disclose the existence of or facts
     surrounding any proposed or pending material developments; (B) if the
     underwriters have notified NAS that market conditions are such as to
     recommend deferral; (C) pending the completion of year-end financial
     statements or quarterly earnings releases; or (D) if an offering by NAS of
     any securities is pending; provided, however, that any deferral pursuant to
     clauses (A), (B), (C) or (D) of this paragraph shall not in the aggregate
     be for more than 90 days.

          (ii)  use its reasonable efforts to cause to be registered or
     qualified the securities covered by such Registration Statement under such
     securities or Blue Sky laws in such jurisdictions within the United States
     as any Selling Shareholder may reasonably request; provided, however, that
     NAS reserves the right, in its sole discretion, not to cause to be
     registered or qualified such securities in any jurisdiction where NAS would
     be

                                       21
<PAGE>

     required in connection therewith to execute a general consent to service or
     to qualify as a foreign corporation or to subject itself to taxation;

          (iii) maintain the effectiveness of any Registration Statement
     hereunder for 90 days or such longer period as may be required by the
     Securities Act to enable any Selling Shareholder and the underwriters, if
     any, to complete such offering;

          (iv)  promptly notify each Selling Shareholder of the happening of any
     event as a result of which any preliminary prospectus or prospectuses
     included in any Registration Statement hereunder includes an untrue
     statement of a material fact or omits to state any material fact required
     to be stated therein or necessary to make the statements not misleading in
     light of the circumstances then existing;

          (v)   have the right to reasonably approve the choice of lead
     underwriter for underwritten offerings initiated by the Holders under
     Section 9.7(b);

          (vi)  furnish, at the request of any Selling Shareholder, an opinion,
     dated the date the Registration Statement became effective, of counsel
     representing NAS (which may be in-house counsel) for the purposes of such
     registration, addressed to the underwriters, if any, and to such Selling
     Shareholder as to such legal matters as such Selling Shareholder shall
     reasonably request; and

          (vii) furnish, at the request of any Selling Shareholder, a letter,
     dated the date the Registration Statement became effective, of independent
     certified public accountants of NAS, addressed to the underwriters, if any,
     and to such Selling Shareholder as to such accounting matters as such
     Selling Shareholder shall reasonably request.

     (f)  The obligations of NAS to cause a Registration Statement to be
prepared pursuant to the provisions of this Section 9.7 and each Selling
Shareholder's right to have shares of Common Stock included in any Registration
Statement pursuant to the provisions of this Section 9.7 shall be subject to the
following conditions:

          (i)   Each Selling Shareholder shall furnish to NAS in writing such
     information and documents as, in the opinion of NAS's counsel, may be
     reasonably required to properly cause to be prepared such Registration
     Statement in accordance with applicable provisions of the Securities Act
     and the SEC's regulations thereunder or federal or state securities or Blue
     Sky laws and regulations then in effect; and

          (ii)  If a Selling Shareholder desires to sell and distribute such
     shares of Common Stock over a period of time, or from time to time,
     pursuant to a Registration Statement prepared pursuant to the provisions of
     this Section 9.7, then such Selling Shareholder shall execute and deliver
     to NAS such written undertakings as NAS and its counsel may reasonably
     require in order to assure full compliance with the relevant provisions of
     the Securities Act and the SEC's regulations thereunder or other federal or
     state securities or Blue Sky laws and regulations as then in effect.

                                       22
<PAGE>

      (g)  The Selling Shareholder will pay or cause to be paid all fees and
expenses (including all Blue Sky, New York Stock Exchange and National
Association of Securities Dealers, Inc. filing and registration fees, accounting
fees and disbursements, printing costs, attorneys' fees and disbursements)
arising out of the preparation, filing, amending and supplementing of a
Registration Statement pursuant to Section 9.7(b) hereof in which only the
Selling Shareholder participates and the amount of such fees and expenses that
are reasonably allocable to the Selling Shareholder for a Registration Statement
used under Section 9.7(c) or a Registration Statement based on the number of
shares offered by the Selling Shareholders relative to the number of other
shares offered by NAS or on behalf of any of its other holders.

      (h)  In no event shall NAS be required to maintain the effectiveness of
any Registration Statement for more than 90 days.

9.8   Listing

      Upon SBC's request, NAS will use its best efforts, and diligently take all
steps necessary, to list for trading on the Nasdaq or, if at the time of
issuance any Common Stock is listed on any securities exchange, to list on each
such exchange, the Common Stock to be issued to SBC upon conversion of the
Preferred Shares (promptly after such Common Stock is issued).

9.9   Issuance of Other Securities

      NAS shall not issue or agree to issue any securities of NAS to any Person
with voting rights that are more favorable in any material respect than the
voting rights of the Preferred Shares.

9.10  Further Assurances

      At any time or from time to time after the Closing Date, NAS shall execute
and deliver any further instruments or documents, and take all such further
action as SBC may reasonably request, in order to effect this Agreement and to
issue to SBC the Preferred Shares free and clear of all Liens except for Liens
as SBC may cause to attach to the Preferred Shares.

9.11  Use of Proceeds

      NAS shall use at least 50% of the Purchase Price for the purpose of more
closely aligning its network and business operations with the future network and
business operations of SBC Telecom, Inc., as outlined in the Summary of
Operating Agreement attached as Exhibit C hereto. The remainder of the Purchase
Price shall be available for general corporate purposes as determined by NAS.

                                       23
<PAGE>

9.12  Definitive Operating Agreement

      Promptly following the execution of this Agreement, NAS shall negotiate in
good faith the Definitive Operating Agreement. The Definitive Operating
Agreement shall contain the substance of the terms and conditions set forth in
the Summary of Operating Agreement attached as Exhibit C and such other terms
and conditions as the parties may mutually agree upon.

9.13  Right of Primary Offer

      Subject to the terms and conditions specified in this Section 9.13, NAS
hereby grants to each Holder, a right of primary offer with respect to future
sales by NAS of its New Securities (as defined in Section 9.13(d)(i)) after the
date hereof.

      (a)  In the event NAS proposes to issue New Securities, it shall give each
Holder written notice (the "Notice") of its intention stating: (i) a description
of the New Securities it proposes to issue, (ii) the number of shares of New
Securities it proposes to offer, (iii) the price per share at which, and other
terms on which, it proposes to offer such New Securities, and (iv) the number of
shares that the Holder has the right to purchase under this Section 9.13, based
on the Holder's Percentage (as defined in Section 9.13(d)(ii)).

      (b)  Within 10 Business Days after the Notice is given, the Holder may
elect to purchase, at the price specified in the Notice, up to the number of
shares of the New Securities proposed to be issued equal to the Holder's
Percentage. An election to purchase shall be made in writing and must be given
to NAS within such 10 Business Day period. The closing of the sale of New
Securities by NAS to the participating Holder upon exercise of its rights under
this Section 9.13 shall take place simultaneously with the closing of the sale
of New Securities to third parties.

      (c)  NAS shall have 90 days after the last date on which the Holder's
right of first offer lapsed to enter into an agreement (pursuant to which the
sale of New Securities covered thereby shall be closed, if at all, within 45
days from the execution thereof) to sell the New Securities which the Holder did
not elect to purchase under this Section 9.13, at or above the price and upon
terms not materially more favorable to the purchasers of such securities than
the terms specified in the initial Notice given in connection with such sale. In
the event NAS has not entered into an agreement to sell the New Securities
within such 90 day period (or sold and issued New Securities in accordance with
the foregoing within 45 days from the date of such agreement), NAS shall not
thereafter issue or sell any New Securities without first offering such New
Securities to the Holder in the manner provided in this Section 9.13.

      (d)  Definitions:

           (i)  "New Securities" shall mean any shares of, or securities
      convertible into or exercisable for any shares of, any class of NAS's
      capital stock; provided that "New Securities" does not include: (A)
      securities issued pursuant to the acquisition of another business entity
      by NAS by merger, purchase of substantially all of the assets of such

                                       24
<PAGE>

      entity, or other reorganization whereby NAS owns not less than a majority
      of the voting power of such entity; (B) shares of NAS's Common Stock,
      options or warrants to purchase shares of NAS's Common Stock, and the
      shares of Common Stock issuable upon exercise of such options or warrants,
      issued pursuant to any arrangement approved by the Board of Directors to
      employees, officers and directors of, or consultants, advisors or other
      Persons performing services for, NAS; (C) shares of NAS's Common Stock
      issued in connection with any stock split, stock dividend or
      recapitalization of NAS; or (D) shares of NAS's Common Stock issued upon
      exercise of warrants, options or convertible securities if the issuance of
      such warrants, options or convertible securities was a result of the
      exercise of the right of first offer granted under this Section 9.13 or
      was subject to the right of first offer granted under this Section 9.13.

           (ii) The applicable "Percentage" for each Holder shall be the number
      of shares of New Securities calculated by dividing (A) the total number of
      shares of Common Stock owned by the Holder (assuming conversion of all
      outstanding convertible securities and exercise of all outstanding options
      and warrants) by (B) the total number of shares of Common Stock
      outstanding at the time the Notice is given (assuming conversion of all
      outstanding convertible securities and exercise of all outstanding options
      and warrants).

9.14  Government License Application Amendment

      NAS shall amend its pending applications for government licenses to cover
the transactions contemplated by this Agreement and shall use its reasonable
best efforts to have those applications, as amended, approved.

Section 10:  Termination
------------------------

10.1  Terminating Events

      This Agreement may be terminated:

      (a)  By the mutual written consent of NAS and SBC; or

      (b)  By NAS, by ten (10) Business Days written notice to SBC (if NAS is
not then materially in default or breach of this Agreement), if SBC shall
default in any material respect in the performance of any of its obligations
under this Agreement, and such default or breach has not been cured by SBC
within seven (7) Business Days following receipt of written notice from NAS of
NAS's intention to terminate this Agreement; or

      (c)  By SBC, by ten (10) Business Days written notice to NAS (if SBC is
not then materially in default or breach of this Agreement), if NAS shall
default in any material respect in the performance of any of its obligations
under this Agreement, and such default or breach has

                                       25
<PAGE>

not been cured by NAS within seven (7) Business Days following receipt of
written notice from SBC of SBC's intention to terminate this Agreement; or

      (d)  By either SBC or NAS if the Closing has not occurred on or before
July 31, 2000 (provided that the right to terminate this Agreement under this
Section 10.1(d) shall not be available to any party whose breach of any
obligation under this Agreement has been the cause of or resulted in the failure
of the Closing to occur on or before such date).

10.2  Effect on Obligations

      In the event of any termination of this Agreement pursuant to Section
10.1(a) or 10.1(d), neither SBC nor NAS shall have any further liability
hereunder, except with respect to the confidentiality provisions hereof. In the
event of a termination under Section 10.1(b) or 10.1(c), both parties shall
retain all their rights at law or in equity.

Section 11: Indemnification
---------------------------

11.1  Indemnification by NAS

      (a)  NAS hereby agrees to indemnify SBC and its Affiliates and their
respective officers and directors against and hold them harmless from any Losses
suffered or incurred by any such Indemnified Party for or on account of or
arising from or in connection with any breach of any representation, warranty or
covenant of NAS contained in this Agreement, provided, however, that NAS shall
not have any liability under this Section 11.1 unless the aggregate of all
Losses relating thereto exceed on a cumulative basis $750,000.00, and then only
to the extent of such excess, and (ii) in excess of the Purchase Price. SBC
acknowledges and agrees that its sole and exclusive remedy with respect to any
and all claims for monetary damages relating to the subject matter of this
Agreement shall be pursuant to the indemnification provisions set forth in this
Section 11.

      (b)  NAS agrees to indemnify and hold harmless each Selling Shareholder
and each Person, if any, who controls (within the meaning of Section 15 of the
Securities Act and Section 20 of the 34 Act) such Selling Shareholder (a
"Control Person") against any Losses to which such Selling Shareholder or any
such Control Person may become subject, insofar as such Losses arise out of or
are based upon any untrue statement or alleged untrue statement of any material
fact contained in any preliminary or final Registration Statement prepared
pursuant to Section 9.7 of this Agreement or prospectus with respect thereto, or
any amendment or supplement thereto, or arise out of or are based upon the
omission or alleged omission to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading;
provided, however, that NAS will not be liable in any case to the extent that
any such Losses arise out of or are based upon an untrue statement or alleged
untrue statement or omission or alleged omission from any of such documents in
reliance upon and in conformity with written information furnished by or on
behalf of such Selling Shareholder or any such Control Person specifically for
use in the preparation thereof.

                                       26
<PAGE>

11.2  Indemnification by SBC

      (a)  SBC hereby agrees to indemnify NAS and its Affiliates and their
respective officers and directors against and hold them harmless from any Losses
suffered or incurred by any such Indemnified Party for or on account of or
arising from or in connection with any breach of any representation, warranty or
covenant of SBC contained in this Agreement, provided, however, that SBC shall
not have any liability under this Section 11.2 unless the aggregate of all
Losses relating thereto exceed on a cumulative basis $750,000.00, and then only
to the extent of such excess. NAS acknowledges and agrees that its sole and
exclusive remedy with respect to any and all claims for monetary damages
relating to the subject matter of this Agreement shall be pursuant to the
indemnification provisions set forth in this Section 11.

      (b)  SBC and any other Selling Shareholder to whom SBC's rights under this
Agreement have been transferred will, severally and not jointly, indemnify and
hold harmless NAS and each of its directors, officers and each Person, if any,
who controls (within the meaning of Section 15 of the Securities Act and Section
20 of the 34 Act) NAS (a "Company Control Person") to the same extent as set
forth in the foregoing indemnity from NAS to each Selling Shareholder set forth
in Section 11.1(b), but only with reference to written information included in
any preliminary or final Registration Statement prepared pursuant to Section
9.7 of this Agreement or prospectus with respect thereto, or amendment or
supplement thereto, furnished by or on behalf of such Selling Shareholder
specifically for use in the preparation of such documents.

11.3  Losses

      The amount of any Losses for which indemnification is provided under this
Section 11 shall be net of any amounts recovered or recoverable by the
Indemnified Party under insurance policies with respect to such Losses and shall
be increased to take account of any Tax cost to the Indemnified Party and
reduced to take account of any Tax benefit to the Indemnified Party arising from
the incurrence or payment of any Losses.

11.4  Survival

      The representations and warranties made by NAS contained in Section 7
hereof, and the obligation of NAS to indemnify SBC pursuant to Section 11.1
hereof, shall survive the execution and delivery of this Agreement, any
examination or due diligence inquiry by a party and the Closing until the date
which is one year after the Closing Date, except that the representations and
warranties made by NAS in Section 7.8 (Title to Preferred Shares; Absence of
Liens) shall survive for the applicable statute of limitations. The
representations and warranties made by SBC contained in Section 6 hereof, and
the obligation of SBC to indemnify SBC pursuant to Section 11.2 hereof, survive
the execution and delivery of this Agreement, any examination or due diligence
inquiry by a party and the Closing until the date which is one year after the
Closing Date. All covenants and agreements of NAS or SBC contained in this
Agreement (which terms do not include representations and warranties) shall
survive the Closing for a period of one year

                                       27
<PAGE>

unless otherwise expressly provided herein. The obligations to indemnify and
hold harmless a party hereto, pursuant to Section 11.1 and Section 11.2 hereof,
shall survive only until the expiration of the applicable survival period for
the representation and warranty or covenant under which the claim for
indemnification is being made; provided, however, that such obligations to
indemnify and hold harmless shall not terminate with respect to any item as to
which the Person to be indemnified shall have, before the expiration of the
applicable period, previously made a claim by delivering a notice (stating in
reasonable detail the basis of such claim) to the party to be providing the
indemnification.

11.5  Procedures Relating to Third Party Claims

      In order for a party (the "Indemnified Party") to be entitled to any
indemnification provided for under this Agreement in respect of, arising out of
or involving a claim or demand made by any Person against the Indemnified Party
(a "Third Party Claim"), such Indemnified Party must notify the indemnifying
party in writing of the Third Party Claim within 10 Business Days after receipt
by such Indemnified Party of written notice of the Third Party Claim; provided,
however, that failure to give such notification shall not affect the
indemnification provided hereunder except to the extent the indemnifying party
shall have been actually prejudiced as a result of such failure (except that the
indemnifying party shall not be liable for any expenses incurred during the
period in which the Indemnified Party failed to give such notice). Thereafter,
the Indemnified Party shall deliver to the indemnifying party, within five
Business Days after the Indemnified Party's receipt thereof copies of all
notices and documents (including court papers) received by the Indemnified Party
relating to the Third Party Claim.

      If a Third Party Claim is made against an Indemnified Party, the
indemnifying party will be entitled to participate in the defense thereof and
upon notice to the Indemnified Party to assume the defense thereof provided that
(i) the indemnifying party's counsel is reasonably satisfactory to the
Indemnified Party and (ii) the indemnifying party shall thereafter consult with
the Indemnified Party upon the Indemnified Party's request for such consultation
from time to time with respect to such suit, action or proceeding. If the
indemnifying party assumes such defense, the Indemnified Party shall have the
right (but not the duty) to participate in the defense thereof and to employ
counsel, at its own expense, separate from the counsel employed by the
indemnifying party. The indemnifying party shall be liable for the fees and
expenses of counsel employed by the Indemnified Party for any period during
which the indemnifying party has not assumed the defense thereof. Should the
indemnifying party so elect to assume the defense of a Third Party Claim, the
indemnifying party will not be liable to the Indemnified Party for any legal
expenses subsequently incurred by the Indemnified Party in connection with the
defense thereof. Whether or not the indemnifying party chooses to defend or
prosecute any Third Party Claim, all of the parties hereto shall cooperate in
the defense or prosecution thereof. Such cooperation shall include the retention
and (upon the indemnifying party's request) the provision to the indemnifying
party of records and information which are reasonably relevant to such Third
Party Claim, and making employees available on a mutually convenient basis to
provide additional information and explanation of any material provided
hereunder. Whether or not the indemnifying party shall have assumed the defense
of a Third Party Claim, the Indemnified Party

                                       28
<PAGE>

shall not admit any liability with respect to, or settle, compromise or
discharge, such Third Party Claim without the indemnifying party's prior written
consent.

      Any payment pursuant to this Section 11.5 shall be made not later than 15
days after receipt by the indemnifying party of written notice from the
Indemnified Party stating that any Third Party Claim has been paid by any
Indemnified Party and the amount thereof and the indemnity payment requested.

Section 12:  Arbitration
------------------------

12.1  Resolution of Disputes

      (a)  The parties shall attempt in good faith to resolve any controversy,
dispute or claim arising out of or relating to this Agreement or the breach,
termination, enforceability or validity thereof (collectively, a "Dispute")
promptly by negotiation between officers or employees who have authority to
settle the Dispute. Either party may give the other a written notice (a "Dispute
Notice") setting forth with reasonable specificity the nature of the Dispute and
the identity of such party's representatives who will attend and participate in
the meeting at which the parties will attempt to settle the Dispute. Following
the receipt of a Dispute Notice, the representatives of both parties shall meet
as soon as is practicable at a mutually acceptable time and place to negotiate
in good faith a settlement of the Dispute, and shall meet thereafter as they
reasonably deem necessary. All negotiations pursuant to this Section 12.1(a)
shall be confidential and shall be treated as compromise and settlement
negotiations. Nothing said or disclosed, nor any document produced, in the
course of such negotiations which is not otherwise independently discoverable
shall be offered or received as evidence or used for impeachment or for any
other purpose in any current of future arbitration or litigation.

      (b)  If the Dispute has not been resolved within 30 days after the receipt
of a Dispute Notice through negotiation as provided in Section 12.1(a), then the
Dispute shall be finally settled by arbitration in accordance with the
commercial arbitration rules of the American Arbitration Association ("AAA")
then in effect. However, in all events, the arbitration provisions in this
Section 12 shall govern over any conflicting rules that may now or hereafter be
contained in the AAA rules. The arbitration shall be held in Washington, D.C.,
unless the parties mutually agree to have the arbitration held elsewhere, and
Judgment upon the award made therein may be entered by any court having
jurisdiction in the United States; provided, however, that nothing contained in
this Section 12 shall be construed to limit or preclude a party from bringing
any action in any court of competent jurisdiction for injunctive or other
provisional relief to compel another party to comply with its obligations under
this Agreement during the pendency of the arbitration proceedings. Any Judgment
upon the award rendered by the arbitrators may be entered in any court having
jurisdiction over the subject matter hereof. The arbitrator shall have the
authority to grant any equitable and legal remedies that would be available in
any judicial proceeding instituted to resolve any claim hereunder.

                                       29
<PAGE>

12.2  Arbitrators

      Any such arbitration will be conducted before three (3) arbitrators, one
of which shall be chosen by NAS, one of which shall be chosen by SBC, and the
third chosen by the other two arbitrators. Each person chosen to serve as an
arbitrator shall be a neutral and impartial attorney who has had training and
experience as an arbitrator. The decision of a majority of the arbitrators will
be the decision of the arbitrators. The arbitrators shall permit such discovery
of information related to the controversy or claim in arbitration as they shall
determine is appropriate in the circumstances, taking into account the needs of
the parties and the desirability of making discovery expeditious and cost-
effective.

12.3  Costs and Fees

      All fees and expenses of the arbitrators, expenses for hearing facilities
and other expenses of the arbitration shall be borne equally by the parties
unless the arbitrators in the award assess such fees and expenses other than
equally against the parties. Each party shall bear the fees and expenses of its
own attorneys and witnesses except to the extent otherwise provided in this
Agreement or by law; provided, that if the arbitrators determine that the claim
or defense of any party was frivolous or lacked a reasonable basis in fact or
law, the arbitrators may assess against such party all or part of the fees and
expenses of attorneys and witnesses for the other party.

12.4  Burden of Proof

      For any Dispute submitted to arbitration, the burden of proof will be as
it would be if the claim were litigated in a judicial proceeding.

12.5  Award

      Upon the conclusion of any arbitration proceedings hereunder, the
arbitrators will render findings of fact and conclusions of law and a written
opinion setting forth the basis and reasons for any decision reached and will
deliver such documents to each party to this Agreement along with a signed copy
of the award.

12.6  Agreement Controls

      The arbitrators chosen in accordance with these provisions will not have
the power to alter, amend or otherwise affect the terms of these arbitration
provisions or the provisions of this Agreement.

                                       30
<PAGE>

Section 13:  Miscellaneous
--------------------------

13.1  Entire Agreement; Amendment

      This Agreement (including the attached Schedules and Exhibits) constitutes
the sole understanding of the parties with respect to the subject matter hereof,
and supersedes all prior oral or written agreements, commitments or
understandings with respect to such matters.  No amendment, modification or
alteration of the terms or provisions of this Agreement shall be binding unless
the same shall be in writing and duly executed by the parties hereto.

13.2  Successors and Assigns

      This Agreement may not be assigned by either NAS or SBC without the
consent of the other party (which consent shall not be unreasonably withheld)
except that SBC may assign this Agreement to any Wholly-Owned SBC Subsidiary
that agrees to be bound by all of the terms hereof, and provided that no such
permitted assignment shall relieve the parties hereto of any liability for a
breach of this Agreement by such party or its assignee. This Agreement shall be
binding upon and shall inure to the benefit of the parties hereto and their
respective heirs or successors in interest.

13.3  Rights and Remedies

      Unless otherwise provided herein, the rights and remedies of the parties
hereunder shall not be mutually exclusive, and the exercise of one or more
provisions of this Agreement shall not preclude the exercise of any other
provisions. Each of the parties confirms that damages at law may be an
inadequate remedy for a breach or threatened breach of any provision hereof. The
respective rights and obligations hereunder shall be enforceable by specific
performance, injunction or other suitable remedy, it being the intention of this
Section 13.3 to make clear the agreement of the parties that the respective
rights and obligations of the parties hereunder shall be enforceable in equity
as well as at law or otherwise.

13.4  Counterparts

      This Agreement may be executed in one or more counterparts, each of which
shall for all purposes be deemed to be an original and all of which shall
constitute the same instrument.

13.5  Modification and Waiver

      At any time on or prior to the Closing Date, the parties by mutual
agreement may (a) extend the time for the performance of any of the obligations
or other acts of the other parties hereto, (b) waive any inaccuracies in the
representations and warranties contained herein or in any document delivered
pursuant hereto, or (c) waive compliance with any of the agreements or
conditions contained herein. Any agreement on the part of a party hereto to any
such extension or waiver shall only be valid if set forth in an instrument in
writing signed on behalf of such party.

                                       31
<PAGE>

13.6  Expenses

      Except as specifically provided herein, SBC and NAS shall each pay all
costs and expenses incurred by it or on its behalf in connection with this
Agreement and the transactions contemplated hereby, including, without limiting
the generality of the foregoing, fees and expenses of its own consultants,
accountants and counsel.

13.7  Notices

      Any notice, request, instruction or other document to be given hereunder
by any party hereto to any other party shall be in writing and shall be deemed
given upon receipt if delivered personally or by telex or facsimile, the next
day if by express mail or three days after being sent by registered or certified
mail, return receipt requested, postage prepaid to the following addresses (or
at such other address for a party as shall be specified by like notice provided
that such notice shall be effective only after receipt thereof):

If to SBC:                         James Kahan
                                   Senior Vice President -
                                   Corporate Development
                                   SBC Communications Inc.
                                   175 East Houston Street
                                   San Antonio, TX 78205
                                   Fax:   210-351-5034
                                   Voice: 210-351-5030

With a copy (which shall           Michael A. Meyer
not constitute notice) to:         General Attorney
                                   SBC Communications Inc.
                                   175 East Houston Street
                                   San Antonio, TX 78205
                                   Fax:   210-351-3488
                                   Voice  210-351-2165

If to NAS:                         Jonathan P. Aust
                                   President and Chief
                                   Executive Officer
                                   Network Access Solutions
                                   100 Carpenter Drive
                                   Sterling, VA 20165
                                   Fax:   703-742-7706
                                   Voice: 703-995-1682

                                       32
<PAGE>

With a copy (which shall           Worth D. MacMurray
not constitute notice) to:         Vice President, Legal and
                                   Strategic Planning
                                   Network Access Solutions
                                   100 Carpenter Drive
                                   Sterling, VA 20165
                                   Fax:   703-995-2180
                                   Voice: 703-995-2695

13.8  Severability

      In case any one or more of the provisions contained in this Agreement
shall for any reason be held to be invalid, illegal or unenforceable in any
respect by a court or other authority of competent jurisdiction, such
invalidity, illegality or unenforceability shall not affect any other provision
hereof and this Agreement shall be construed as if such invalid, illegal or
unenforceable provision had never been contained herein and, in lieu of each
such illegal, invalid or unenforceable provision, there shall be added
automatically as a part of this Agreement a provision as similar in terms to
such illegal, invalid or unenforceable provision as may be possible and be
legal, valid and enforceable, it being the intent of the parties to maintain the
benefit of the bargain for all parties.

13.9  Governing Law

      This Agreement shall be construed in accordance with and governed by the
laws of the State of Delaware applicable to agreements made and to be performed
wholly within such jurisdiction.

13.10 Rules of Construction

      Words used in this Agreement, regardless of the gender and number
specifically used, shall be deemed and construed to include any other gender and
any other number as the context requires. As used in this Agreement, the word
"including" is not limiting, and the word "or" is not exclusive. Except as
specifically otherwise provided in this Agreement in a particular instance, a
reference to a Section, Schedule or Exhibit is a reference to a Section of this
Agreement or a Schedule or Exhibit hereto, and the terms "this Agreement,"
"hereof," "herein," and other like terms refer to this Agreement as a whole,
including the Schedules to this Agreement, and not solely to any particular part
of this Agreement. The descriptive headings in this Agreement are inserted for
convenience of reference only and are not intended to be part of or to affect
the meaning or interpretation of this Agreement. The parties to this Agreement
do not intend that NAS Employees or any other Person shall obtain any rights as
third party beneficiaries of this Agreement.

                                       33
<PAGE>

13.11 Ownership Limitation

      Notwithstanding anything else to the contrary in this Agreement, nothing
set forth in this Agreement shall be construed or interpreted to provide SBC
with the right to Beneficially Own any shares of Common Stock or other class of
capital stock of NAS to the extent that it would violate any Legal Requirements
of the FCC or any other Governmental Authority.

      IN WITNESS WHEREOF, the parties hereto have signed this Agreement, or have
caused this Agreement to be signed in their respective names by an officer,
hereunto duly authorized, on the date first above written.

                                        NETWORK ACCESS SOLUTIONS CORPORATION

                                        By:____________________________________
                                           Name:_______________________________
                                           Title:______________________________

                                        SBC COMMUNICATIONS INC.

                                        By:____________________________________
                                           Name:_______________________________
                                           Title:______________________________

                                       34

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00004-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00004-of-00352.parquet"}]]