<PAGE>
                                                                 Exhibit 10.1.11
                                  OFFICE LEASE

             SOFI-IV SIM OFFICE INVESTORS II, LIMITED PARTNERSHIP

                                    Landlord

                                       and

              Advanced Telecommunications, Inc. a Delaware corp.

                                     Tenant

                             Dated: December 1, 1999
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TABLE OF CONTENTS

                                TABLE OF CONTENTS

ARTICLE 1     SUMMARY OF BASIC TERMS

ARTICLE 2     DELIVERY, TERM AND CONSTRUCTION
    2.1       Term
    2.2       Memorandum
    2.3       Area Measurement
    2.4       Condition

ARTICLE 3     USE OF PREMISES
    3.1       Permitted Uses
    3.2       Insurance Restrictions
    3.3       Improvements
    3.4       Prohibitions
    3.5       Common Areas
    3.6       Rules and Regulations
    3.7       Compliance with Law
    3.8       Audit
    3.9       Parking
   3.10       Keys, Locks and Access Cards

ARTICLE 4     SECURITY DEPOSIT AND GUARANTIES

ARTICLE 5     RENT
    5.1       Base Rent
    5.2       Late Charges and Interest
    5.3       Excise Taxes
    5.4       Obligations are Rent
    5.5       Proration

ARTICLE 6     OPERATING COSTS
    6.1       Tenant's Share
    6.2       Estimates
    6.3       Annual Reconciliation
    6.4       Partial Year Proration, Variable Cost Adjustment
    6.5       Operating Costs
    6.6       Exclusions

ARTICLE 7     TAXES

ARTICLE 8     INSURANCE AND INDEMNITY
    8.1       Insurance Policies
    8.2       Policy Requirements
    8 3       Evidence of Coverage
    8 4       Indemnity and Exculpation
    8.5       Landlords Policies

ARTICLE 9     FIRE AND CASUALTY
    9.1       Termination Rights
    9.2       Restoration
    9.3       Abatement
    9.4       Demolition of Project
    9.5       Agreed Remedies

ARTICLE 10    CONDEMNATION
   10.1       Automatic Termination
   10.2       Optional Termination
   10.3       Award


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ARTICLE 11    MAINTENANCE
   11.1       By Tenant
   11.2       By Landlord

ARTICLE 12    UTILITIES

ARTICLE 13    LANDLORD RIGHT OF ENTRY

ARTICLE 14    SIGNS

ARTICLE 15    TENANT ALTERATIONS
   15.1       Tenant Alterations
   15.2       Tenant Installations
   15.3       Mechanics Liens

ARTICLE 16    ASSIGNMENT AND SUBLETTING
   16.1       Consent Required
   16.2       Requests for Approval
   16.3       Continued Responsibility
   16.4       Excess Proceeds
   16.5       Limitations
   16.6       No Waiver
   16.7       Transfer by Landlord

ARTICLE 17    SUBORDINATION AND A1TORNMENT
   17.1       Subordination
   17.2       Lender Protection
   17.3       Documentation
   17.4       Other Transactions

ARTICLE 18    ESTOPPEL CERTIFICATES

ARTICLE 19    QUIET ENJOYMENT

ARTICLE 20    SURRENDER AND HOLDOVER
   20.1       Surrender
   20.2       Holdover

ARTICLE 21    BREACH, DEFAULT, AND REMEDIES
   21.1       Default
   21.2       Remedies
   21.3       Subtenancies

ARTICLE 22    LANDLORD LIABILITY

ARTICLE 23    NOTICES

ARTICLE 24    BROKERAGE

ARTICLE 25    RELOCATION

ARTICLE 26    GENERAL
   26.1       Severability
   26.2       No Waiver
   26.3       Effect of Payment
   26.4       Delay
   26.5       Lender Notice
   26.6       No Offer


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   26.7       Successors
   26.8       Integration
   26.9       Waiver of Jury Trial
  26.10       Governing Law
  26.11       Deadlines Enforceable
  26.12       Counterparts
  26.13       Additional Provisions

ARTICLE 27      SERVICES

     A.       Landlord's Obligations
     B.       Electrical Service
     C.       Restoration of Service/Tenant Self-Help Remedy
     D.       Generator & HVAC Access

ARTICLE 28    RISERS & CONDUIT ACCESS

ARTICLE 29    BATTERY INSTALLATION

ARTICLE 30    GROUNDING RISER

ARTICLE 31    ANTENNAE

ARTICLE 32    FIRE PROTECTION & LIFE SAFETY

ARTICLE 33    HAZARDOUS SUBSTANCES

ARTICLE 34    EXPRESS WAIVER OF LANDLORD'S LIEN

ARTICLE 35    ALLOWABLE USE OF CERTAIN HAZARDOUS MATERIALS

EXHIBITS

EXHIBIT A -   THE PREMISES
EXHIBIT A-1 - FLOOR PLAN
EXHIBIT B -   CONSTRUCTION PROVISIONS
EXHIBIT C -   RULES AND REGULATIONS


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OFFICE LEASE

SOFI-IV SIM OFFICE INVESTORS II LIMITED PARTNERSHIP, an Delaware limited
partnership ("Landlord"), hereby leases the Premises described below, for the
Term and on the terms and conditions set forth in this Lease, to:

Advanced Telecommunications, Inc. a Delaware corp.

                                                                     ("Tenant").


ARTICLE I SUMMARY OF BASIC TERMS

1.1  The Premises: Suite #500 in the Building consisting of approximately 6,028
     square feet of rentable area as illustrated on the attached Exhibit A. A
     floor plan for the floor(s) on which the Premises is located is attached as
     Exhibit A-1.

1.2  The Building: The building is located at 2600 North Central Avenue,
     Phoenix, Arizona.

1.3  "Project" means the Building identified in Section 1.2, and all lands and
     facilities used in connection with the Building as reasonably determined
     from time to time by Landlord. The Project consists of approximately
     322,000 square feet of rentable area.

1.4  Names of Guarantor & None

1.5  Security Deposit: $12,000.00.

1.6  The Term: Ten (10) years and four (4) months, beginning on the Commencement
     Date and ending on the Expiration Date.

1.7  Commencement and Expiration Dates: January 15, 2000, and May 15, 2010,
     respectively, subject to the provisions of Exhibit

B.

1.8  Base Rent:

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Lease Year    Annual Base Rent      Base Rent Per Square Foot  Monthly Base Rent
--------------------------------------------------------------------------------
   1           $120,560.00               $20.00/sq. ft.          $ 10,046.67
--------------------------------------------------------------------------------
   2           $124,176.80               $20.60/sq. ft.           $10,348.07
--------------------------------------------------------------------------------
   3           $127,914.16               $21.22/sq. ft.           $10,659.51
--------------------------------------------------------------------------------
   4           $131,772.08               $21.86/sq. ft.           $10,981.01
--------------------------------------------------------------------------------
   5           $135,750.56               $22.52/sq. ft.           $11,312.55
--------------------------------------------------------------------------------
   6           $139,849.60               $23.20/sq. ft.           $11,654.13
--------------------------------------------------------------------------------
   7           $144.069.20               $23.90/sq. ft.           $12,005.77
--------------------------------------------------------------------------------
   8           $148,409.36               $24.62/sq. ft.           $12,367.45
--------------------------------------------------------------------------------
   9           $152,870.08               $25.36/sq. ft.           $12,739.17
--------------------------------------------------------------------------------
   10          $157,451.36               $26.12/sq. ft.           $13,120.95
--------------------------------------------------------------------------------

1.9 Tenant's Proportionate Share: 1.87%, consisting of the proportion that the
rentable area of the Premises bears to the rentable area of the Project.


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1.10 Base Year: 2000.

1.11 Description of Tenant's Business: Executive and general office use, the
installation, operation and maintenance of equipment and facilities in
connection with Tenant's telecommunication business, including but nor limited
to telecommunications switch.

1.12 Normal Business Hours: 7:00 a.m. to 6:00 p.m., Monday through Friday, 8 00
a.m. to 1:00 p.m. on Saturday.

1.13 Tenant Improvement Allowance: $5.OO per rentable square foot ($30,140 00).

1.14 Tenant's Address for Pre-occupancy Notices:     730 2nd Ave. South
                                                     # 1200
                                                     Minneapolis. MN 55402

1.15 Landlord's Notice Address:     c/o Scottsdale Property Management 97, L.L.C
                                    9495 E. San Salvador, Suite 100
                                    Scottsdale, AZ 85258

1.16 Tenant's designated broker:      Eric Ham, TELECOM Real Estate Services

11.7 Landlord's designated broker:    Scottsdale Property Management 97, L.L.C.

ARTICLE 2 DELIVERY, TERM AND CONSTRUCTION

2.1 Term. The Term of this Lease, and the dates of commencement and expiration
of the Term, are set forth in Sections 1.6 and 1.7

2.2 Memorandum. At the request of either party at any time following initial
occupancy of the Premises by Tenant, Landlord and Tenant shall execute a written
memorandum reflecting the date of initial occupancy and confirming the
Commencement Date and Expiration Date

2.3 Area Measurement. "Rentable Area" means area measured in accordance with
American National Standard Z65.1-1980, as published by BOMA International.

2.4 Condition. Landlord shall have no obligation to make any improvements or
alterations to the Premises or the Building whatsoever, and Tenant accepts the
Premises in an AS IS condition, with all faults. Notwithstanding the foregoing,
if an Exhibit C is attached to this Lease, Landlord shall cause improvements to
be constructed and alterations to be made in the Premises in accordance with the
provisions of Exhibit B

ARTICLE 3 USE OF PREMISES

3.1 Permitted Uses. Tenant may use and occupy the Premises for the purposes set
forth in Section 1.11 and for no other purpose whatsoever without Landlord's
prior written consent. Tenant shall not use the Premises for any purpose in
violation of exclusive rights granted by Landlord from time to time to any other
Tenant; provided, however, that Landlord shall not grant any exclusive right
that would prevent Tenant from conducting its business as described in Section
1.11.

3.2 Insurance Restrictions. Tenant shall not perform any act which would cause
the cancellation of any insurance policies related to the Project. Tenant shall
reimburse Landlord for any increases in insurance premiums paid by Landlord
directly related to the nature of Tenant's use of the Premises or the nature of
Tenant's business.

3.3 Improvements. If solely due to the nature of Tenant's use of the Premises,
improvements or alterations are necessary to comply with any requirements
imposed by Law or with the requirements of insurance carriers, Tenant shall pay
the entire cost of the improvements or alterations.

3.4 Prohibitions. Tenant shall not cause or maintain any nuisance in or about
the Premises and shall keep the Premises free of debris, rodents, vermin and
anything of a dangerous, noxious or offensive nature or which would create a
fire hazard (through undue


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load on electrical circuits or otherwise) or undue vibration, noise or heat.
Tenant shall not cause the safe floor loading capacity to be exceeded. Tenant
shall not disturb or interfere with the quiet enjoyment of the premises of any
other tenant

3.5 Common Areas. All of the portions of the Project made available by Landlord
for use in common by tenants and their employees and invitees ("Common Areas")
at all times shall remain subject to Landlord's exclusive control and Landlord
shall be entitled to make such changes in the Common Areas as it deems
appropriate. Landlord shall have the right at any time to change the arrangement
and/or locations of entrances, or passageways, doors and doorways, and
corridors, windows, elevators, stairs, toilets or other public parts of the
Building and to change the name, number or designation by which the Building or
the Project is commonly known.

3.6 Rules and Regulations. Tenant shall comply and shall cause its employees to
comply with the rules and regulations for the Project. The current rules and
regulations are attached as Exhibit C. Landlord from time to time by notice to
Tenant may amend the rules and regulations and establish other reasonable
non-discriminatory rules and regulations for the Project

3.7 Compliance with Law. Without in any manner limiting any other provision of
this Lease, Tenant hereby represents and warrants and agrees for the full term
of any obligations under this Lease:

     (a) to comply fully with all federal, state and local laws, rules, orders,
or regulations pertaining to health or the environment ("Environmental Laws"),
including, without limitation, the comprehensive Environmental Response,
Compensation, and Liability Act of 1980, as amended ("CERCLA") and the Resource
Conservation and Recovery Act of 1987, as amended ("RCRA").

     (b) that Tenant will not dispose of nor permit or acquiesce in the disposal
of any waste (including, but not limited to, and paints, solvents, or paint
thinners) products on, under or around the Premises.

     (c) to defend, indemnify and hold harmless Landlord for any and all costs,
claims, demands, damages including attorneys' fees and court costs and
investigatory and laboratory fees, related to any breach of this Lease,
including, without limitation, any adverse health or environmental condition
(including without limitation any violation of Environmental Laws) occurring
during the term of this Lease. This indemnification to Landlord shall survive
the termination of the Lease.

     (d) comply with all reporting obligations imposed under the Federal
Emergency Planning and Community Right to Know Act of 1986 and any similar state
or local laws, rules or regulations.

     (e) comply with all pretreatment requirements imposed by law with respect
to the disposal of waste or effluent into the sanitary sewer system;

     (f) prevent any dumping, spillage, leakage or runoff of substances
regulated by Environmental Laws ("Regulated Substances") into dry wells, storm
drains, water retention areas, Common Areas or any areas where such substances
could be absorbed into the soil;

     (g) obtain and maintain all permits required by federal, state or local
laws, rules or regulations;

     (h) prepare, and upon request provide a copy to Landlord of, all response
plans required by applicable law, and

     (i) not keep, store, or use within the Premises any Regulated Substances
except small quantities that are reasonably necessary for Tenant's business and
customarily associated with office usage, such as copier supplies.

3.8 Audit. At any time and from time to time, Landlord may retain an
environmental consultant or engineer to conduct an audit or environmental
assessment of the Premises and Tenant's compliance with applicable laws, rules
and regulations. Tenant shall extend its full cooperation with the audit or
investigation If Tenant is found not to be substantially in compliance with
applicable law, all reasonable costs associated with the audit or assessment
shall be paid by Tenant to Landlord upon demand; otherwise all costs shall be
borne by Landlord. In addition, Tenant, at Landlord's request from time to time,
shall complete such questionnaires and provide such information with respect to
Tenant's activities and operations on the Premises as Landlord shall reasonably
require.

3.9 Parking . Tenant shall lease the following parking spaces:


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--------------------------------------------------------------------------------
        # of Spaces     Parking Area       Price per Space         Total Price
--------------------------------------------------------------------------------
       Up to 6        open unreserved      @ then current
                                             bldg rates
--------------------------------------------------------------------------------

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

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3.10 Keys, Locks and Access Cards.

     (a) Landlord shall furnish Tenant two keys for each corridor door entering
the Premises. Additional keys will be furnished at a charge by Landlord on an
order signed by Tenant or Tenant's authorized representative. All such keys
shall remain the property of Landlord No additional locks shall be allowed on
any door of the Premises without Landlord's permission. and Tenant shall not
make, or permit to be made any duplicate keys. Upon termination of this Lease,
Tenant shall surrender to Landlord all keys of the Premises, and give to
Landlord the combination of all locks for safes, safe cabinets and vault doors,
if any, in the Premises

     (b) Landlord shall furnish tenant with security access cards for the
Building ("Access Cards"). Access Cards will be furnished at a reasonable charge
by Landlord on an order signed by Tenant or Tenant's authorized representative.
A portion of the charge for the Access Cards may constitute a deposit, the
balance of which shall compensate Landlord for costs, record keeping and other
administrative items in respect of the Access Cards. All such orders shall be
treated as confidential. All such cards shall remain the property of Landlord.
Replacement Access Cards shall be subject to a reasonable charge. Landlord shall
charge Tenant a reasonable transfer fee in connection with a change in the
registration of an Access Card Tenant shall promptly notify Landlord of a lost
Access Card, UNDER NO CIRCUMSTANCES shall tenant label, or in any other way
identify, any Access Cards as to the name of the Building, address of the
Building, or include tenant's personal or company name. Upon termination of any
officer, employee, or any other authorized representative of Tenant, any Access
Card to said person shall be surrendered to Tenant immediately. It shall be the
Tenant's obligation to notify Landlord of all terminated access privileges as
soon as possible following such action. Upon termination of this Lease, Tenant
shall surrender to Landlord all registered Access Cards. The card deposit
portion of the charge paid by Tenant, if any, will be refunded by Landlord
within thirty days, provided all Access Cards are in a reusable condition.

ARTICLE 4 SECURITY DEPOSIT

Upon execution of this Lease Tenant shall deposit with Landlord a security
deposit in the amount set forth in Section 1.5 to secure Tenant's performance of
this Lease. The deposit shall not bear interest, shall not be required to be
maintained in a separate account, and shall be returned, less any unpaid claims
against Tenant, upon the expiration of this Lease and the surrender of
possession of the Premises, to Tenant or the last assignee of Tenant's interest
If Tenant has not been in default under the terms of this Lease for the first
thirty-sixth (36th) months of the lease term, then Landlord shall apply the
Security Deposit towards the rental due for the thirty-seventh (37th) month. If
a Tenant default occurs after the thirty-sixth (36th) month, then upon written
notice from Landlord, Tenant will deposit with Landlord, within thirty days of
said notice, a "new" security deposit of S 12,000.00

ARTICLE 5 RENT

5.1 Base Rent. Tenant shall pay to Landlord, in advance, on the first day of
each calendar month, beginning on the first day of the fourth full calendar
month following the Commencement Date ("Rent Commencement Date"), Base Rent in
the amount set forth in Section 1.8.

5.2 Late Charges and Interest. Tenant shall pay to Landlord a late charge equal
to ten percent (10%) of the amount due if any installment of Base Rent or if any
other amount payable under this Lease is not received by Landlord within five
(5) days after the due date therefor. The parties agree that such late charge
represents a fair and reasonable estimate of the costs Landlord will incur by
reason of such late payment and that such late charge constitutes liquidated
damages to compensate Landlord for costs and inconveniences of special handling
and disruption of cash flow. The assessment or collection of a late charge shall
not constitute the waiver of a default and shall not bar the exercise of other
remedies for nonpayment. In addition to the late charge, all amounts not paid
within ten days after the date due shall bear interest from the date due (i)
until the happening of an Event of Default, at the rate of 12% per annum and
(ii) thereafter, at the rate set forth in Section 2.1.2.


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5.3 Excise Taxes. Tenant shall pay to Landlord all rental, sales, use,
transaction privilege, or other excise tax levied or imposed upon, or measured
by, any amount payable by Tenant under this Lease.

5.4 Obligations Are Rent. All amounts payable to Landlord under this Lease
constitute rent and shall be payable without notice, demand, deduction or offset
to such person and at such place as Landlord may from time to time designate by
written notice to Tenant

5.5 Proration. Base Rent payable with respect to a period consisting of less
than a full calendar month shall be prorated.

ARTICLE 6 OPERATING COSTS

6.1 Tenant's Share. Tenant shall pay to Landlord Tenant's Proportionate Share of
Operating Costs for each calendar year in excess of the Operating Costs for the
Base Year as set forth in Section 1.10.

6.2 Estimates. From time to time Landlord shall by written notice specify
Landlord's estimate of Tenant's obligation under Section 6.1. Tenant shall pay
one-twelfth of the estimated annual obligation on the first day of each calendar
month.

6.3 Annual Reconciliation. Within 120 days after the end of each calendar year,
Landlord shall provide to Tenant a written summary of the Operating Costs for
the calendar year, determined on an accrual basis and broken down by principal
categories of expense. The statement also shall set forth Tenant's Proportionate
Share of Operating Costs and shall show the amounts paid by Tenant on account.
Any difference between Tenant's obligation and the amounts paid by Tenant on
account shall be paid or refunded, as the case may be, within fifteen days after
the statement is provided. Late delivery of the annual statement of Operating
Costs shall not relieve Tenant of any obligation with respect to payment of
Tenant's Proportionate Share of the Operating Costs

6.4 Partial Year Proration; Variable Cost Adjustment. During the first and last
years of the Term, Tenant's responsibility for Operating Costs shall be adjusted
in the proportion that the number of days of that calendar year during which the
Lease is in effect bears to 365. Tenant's obligations under this Article 6 for
the payment of Operating Costs during the Lease Term, including the payment of
any deficiency following receipt of the annual statement under Section 6.3,
shall survive the expiration or termination of this Lease.

6.5 "Operating Costs" consist of all costs of operating, maintaining and
repairing the Project, including, without limitation, the following:

     (a) Premiums for property, casualty, liability, rent interruption or other
insurance.

     (b) Salaries, wages and other amounts paid or payable for personnel
including the Project manager, superintendent, operation and maintenance staff,
and other employees of Landlord involved in the maintenance and operation of the
Project, including contributions and premiums towards fringe benefits,
unemployment and workers compensation insurance, pension plan contributions and
similar premiums and contributions and the total charges of any independent
contractors or managers engaged in the repair, care, maintenance and cleaning of
any portion of the Project.

     (c) Cleaning, including sweeping of parking areas and removal of snow and
ice.

     (d) Landscaping, including irrigating, trimming, mowing, fertilizing,
seeding, and replacing plants.

     (e) Utilities, including fuel, gas, electricity, water, sewer, telephone,
and other services.

     (f) Maintaining, operating, repairing and replacing equipment.

     (g) Other items of repair or maintenance of the Project.

     (h) Policing and security.

     (i) The cost of the rental of any equipment and the cost of supplies used
in the maintenance and operation of the Project.

     (j) Audit fees and the cost of accounting services incurred in the
preparation of statements referred to in this Lease and financial statements,
and in the computation of the rents and charges payable by tenants of the
Project.

     (k) Costs of capital expenditures incurred for the purpose of reducing
Operating Costs, and costs of improvements, repairs, or replacements which
otherwise constitute Operating Costs under this Article but which are properly
charged to capital


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accounts shall not be included in Operating Costs in a single year but shall
instead be amortized over their useful lives, as determined by the Landlord in
accordance with generally accepted accounting principles, and only the annual
amortization amount shall be included in Operating Costs.

     (l) A fee for the administration and management of the Project appropriate
to the nature of the Project as reasonably determined by the Landlord from time
to time.

     (m) Costs of alterations or modifications to the Project necessary to
comply with requirements of applicable law; and

     (n) General and special real and personal property taxes and assessments
for the Project and expenses incurred in efforts to reduce taxes or assessments.

6.6 Exclusions. Notwithstanding anything to the contrary in Section 6.5,
"Operating Costs" shall not include:

     (a) Amounts reimbursed by other sources, such as insurance proceeds,
equipment warranties, judgments or settlements.

     (b) Utilities or other expenses paid directly by tenants to suppliers or
paid by tenants to Landlord for separately metered or special services such as
after-hours air conditioning services.

     (c) Ground rents.

     (d) Payments on any mortgage or other encumbrance.

     (e) Construction of tenant improvements.

     (f) Replacements (but not repairs) of structural elements.

     (g) Leasing commissions.

     (h) General overhead and administrative expenses of Landlord not directly
related to the operation of the Project

ARTICLE 7 TAXES

7.1 Landlord shall pay before delinquent all general and special real property
taxes assessed or levied on the Project, subject to reimbursement under Article
6.

7.2 Tenant shall pay before delinquent all taxes levied or assessed upon,
measured by, or arising from (a) the conduct of Tenant's business; (b)
Tenant's leasehold estate; or (c) Tenant's property.

ARTICLE 8 INSURANCE AND INDEMNITY

8.1 Insurance Policies. Tenant shall, at its expense, take out and keep in full
force and effect the following insurance:

     (a) All-risk property insurance including sprinkler leakage in an amount
equal to the full replacement cost of all property owned by Tenant

     (b) Business interruption insurance with a limit sufficient to insure not
less than a six month loss of income.

     (c) Plate glass insurance coverage

     (d) Comprehensive liability insurance applying to the use and occupancy of
the Premises and the business operated by Tenant, including coverage for
"premises/operations", "products and completed operations", and "blanket
contractual" liabilities, written on an occurrence basis with limits not less
than $1,000,000, naming Landlord, its agents, affiliates and contract property
manager as additional insureds.


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        (e) At all times during the Lease Term, Tenant shall procure and
maintain workers' compensation insurance in accordance with applicable law and
employer's liability insurance with a limit not less than $1,000,000 bodily
injury each accident; $1,000,000 bodily injury by disease - each person; and
$1,000,000 bodily injury by disease - policy limit.

8.2 Policy Requirements. Tenant's insurance policies shall:

     (a) where applicable, contain the mortgagee's standard mortgage clause and
in any event a waiver of any subrogation rights which Tenant's insurers may have
against Landlord and against those for whom the Landlord is in law responsible;

     (b) be taken out with insurers reasonably acceptable to Landlord and be in
a form satisfactory from time to time to Landlord;

     (c) be non-contributing and apply as primary and not as excess to, any
other insurance available to the Landlord;

     (d) not be invalidated with respect to the interests of the Landlord and
the holder of any encumbrance on the Project by reason of any breach or
violation by Tenant of any warranties, representations, declarations or
conditions contained in the policies;

     (e) contain an undertaking by the insurers to notify the Landlord, and the
holder of any encumbrance on the Project designated by Landlord, in writing not
less than thirty days prior to any material change, cancellation or termination;
and

     (f) be satisfactory in form, substance, limits, deductibles and retentions
to Landlord

8.3 Evidence of Coverage. Tenant shall deliver to Landlord certificates of
insurance or, if required by Landlord, certified copies of each such insurance
policy: (a) as soon as practicable after the placing of the required insurance
and (b) periodically thereafter before expiration, renewal or replacement of the
policies then in force. No review or approval of any such insurance certificate
by Landlord shall derogate or diminish Landlord's rights or Tenant's
obligations. Tenant shall not take possession of the Premises without having
complied with the requirements of this Section.

8.4 Indemnity and Exculpation. Tenant shall defend, indemnify and hold Landlord
harmless, regardless of any negligence imputed to Landlord as owner of the real
property involved in an injury, from and against any and all loss, claims,
actions, damages, liability and expense in connection with loss of life,
personal injury, damage to property' or any other loss or injury whatsoever
arising directly or indirectly from or out of this Lease, or any occurrence in,
upon or at the Premises, or the occupancy or use by the Tenant of the Premises,
or any act or omission of Tenant, its agents, servants, employees or invitees.
Tenant shall not be required, however, to indemnify Landlord against a claim
arising from Landlord's active negligence or willful misconduct Landlord shall
not be liable and Tenant hereby waives all claims for any damage to any property
in or about the Premises or the Project or injury or inconvenience to Tenant's
business, by or from any cause whatsoever (including without limiting the
foregoing, rain or water leakage of any character from the roof, windows, walls,
basement, pipes, plumbing works or appliances). Tenant acknowledges that it is
protecting itself against loss by maintaining appropriate insurance coverage.

8.5 Landlord's Policies. No insurable interest is conferred upon Tenant under
any policies of insurance carried by Landlord, and Tenant shall not be entitled
to share or receive proceeds of any insurance policy carried by Landlord.

ARTICLE 9 FIRE AND CASUALTY

9.1 Termination Rights. If all or part of the Premises is rendered untenantable
by damage from fire or other casualty which in Landlord's opinion cannot be
substantially repaired (employing normal construction methods without overtime
or other premium) under applicable laws and governmental regulations within 180
days from the date of the fire or other casualty, then either Landlord or Tenant
may elect to terminate this Lease as of the date of such casualty by written
notice delivered to the other not later than ten days after notice of such
determination is given by Landlord.

9.2 Restoration. If in Landlord's opinion the damage caused by the fire or
casualty can be substantially repaired (employing normal construction methods
without overtime or other premium) under applicable laws and governmental
regulations within 180 days from the date of the fire or other casualty, or if
neither party exercises its right to terminate under Section 9.1, Landlord
shall, but only to the extent that insurance proceeds are available therefor,
repair such damage other than damage to furniture, chattels or trade fixtures
which do not belong to the Landlord, which shall be repaired forthwith by Tenant
at its own expense.

9.3 Abatement. During any period of restoration, the Base Rent payable by Tenant
shall be proportionately reduced to the extent that the Premises are thereby
rendered untenantable from the date of casualty until completion by Landlord of
the repairs to the


                                       7
<PAGE>

Premises (or the part thereof rendered untenantable) or until Tenant again uses
the Premises (or the part thereof rendered untenantable) in its business,
whichever first occurs.

9.4 Demolition of Project. Notwithstanding anything to the contrary in Section
9.1, if all or a substantial part (whether or not including the Premises) of the
Building is rendered untenantable by damage from fire or other casualty to such
a material extent that in the opinion of Landlord the Project must be totally or
partially demolished, whether or not to be reconstructed in whole or in part,
Landlord may elect to terminate this Lease as of the date of the casualty (or on
the date of notice if the Premises are unaffected by such casualty) by written
notice delivered to Tenant not more than sixty days after the date of the fire
or casualty.

9.5 Agreed Remedies. Except as specifically provided in this Article, there
shall be no reduction of rent and Landlord shall have no liability to Tenant
by reason of any injury to or interference with Tenant's business or property
arising from fire or other casualty, howsoever caused, or from the making of
any repairs resulting therefrom in or to any portion of the Project or the
Premises. Tenant waives any statutory or other rights of termination by
reason of fire or other casualty, it being the intention of the parties to
provide specifically and exclusively in this Article for the rights of the
parties with respect to termination of this Lease as a result of a casualty.

ARTICLE 10 CONDEMNATION

10.1 Automatic Termination. If during the Term all or any part of the Premises
is permanently taken for any public or quasi-public use under any statute or by
right of eminent domain, or purchased under threat of such taking, this Lease
shall automatically terminate on the date on which the condemning authority
takes possession of the Premises.

10.2 Optional Termination. If during the term any part of the Project is taken
or purchased by right of eminent domain or in lieu of condemnation, whether or
not the Premises are directly affected, then if in the reasonable opinion of
Landlord substantial alteration or reconstruction of the Project is necessary or
desirable as a result thereof, or the amount of parking available to the Project
is materially and adversely affected, Landlord shall have the right to terminate
this Lease by giving Tenant at least thirty days written notice of such
termination.

10.3 Award. Landlord shall be entitled to receive and retain the entire award
or consideration for the affected lands and improvements and Tenant shall not
have or advance any claims against Landlord for the value of its property or
its leasehold estate or the unexpired term of this Lease or for costs of
removal or relocation or business interruption expense or any other damages
arising out of the taking or purchase. Nothing herein shall give Landlord any
interest in or preclude Tenant from seeking and recovering on its own account
from the condemning authority any award of compensation attributable to the
taking or purchase of Tenant's chattels or trade fixtures or attributable to
Tenant's relocation expenses provided that any such separate claim by Tenant
shall not reduce or adversely affect the amount of Landlord's award. If any
such award made or compensation paid to Tenant specifically includes an award
or amount for Landlord, Tenant shall promptly account therefor to Landlord.

ARTICLE 11 MAINTENANCE

11.1 By Tenant. Tenant shall maintain equipment, alterations or other
improvements whether constructed for Tenant's initial occupancy or made
subsequently pursuant to Article 15, such as supplemental or special cooling
systems not consistent with building standard tenant improvements as established
by the Landlord. If Tenant does not comply with its obligations under this
Article, Landlord may, but need not, make such repairs and replacements or
obtain such service contracts, and Tenant shall pay Landlord the cost thereof
upon demand. Tenant also shall make such repairs and alterations necessary to
comply with the requirements of any governmental or quasi-governmental
authority' having jurisdiction

11.2 By Landlord. Landlord shall maintain the Premises and the improvements
thereon (including all doors, plate glass, and heating, air conditioning,
ventilation, electrical and plumbing systems serving the Premises), in good
condition and repair. Landlord shall provide janitorial services to the Premises
five nights per week. Landlord shall maintain the Project and all Common Areas
in good condition and repair in accordance with standards then prevailing for
comparable properties of like age and character. Landlord shall repair
structural defects in roof or walls and any common utility facilities in the
Common Areas. Landlord shall not be liable or responsible for breakdowns or
temporary interruptions in access or utilities nor for interference with
Tenant's business or Tenant's access to the Premises during the course of
repairs or remedial work.


                                       8
<PAGE>

ARTICLE 12 UTILITIES

Landlord shall supply the following services to assure Tenant's operations in
the Premises 24 hours/day, 365 days/year:

A.   Electrical. Landlord shall provide 800 amps of 480 volt three phase
     electrical power for Tenant's suite (#500) Said power will brought into one
     of the Project's electrical rooms, as shown on Exhibit "E", and it is
     Tenant's responsibility and cost to distribute said power from the
     electrical room to and throughout their suite. Tenant shall obtain its
     electricity directly from Landlord, which shall be separately metered by a
     meter installed by Landlord at its cost, with no mark up.

B.   Heat and air conditioning: SEE ARTICLE 27(D)

C.   Hot and cold water from the regular building outlets for lavatory and
     restrooms and for drinking purposes.

D.   Passenger elevator service in common with other tenants to be provided by
     automatic elevators. Landlord shall have the right to restrict to use of
     elevators for freight purposes to the freight elevator and to hours to be
     reasonably determined by Landlord so long as elevator is reasonably
     available (24 hours/day, 7 days/week), without charge, for Tenant's
     construction purposes. Landlord shall have the right to limit the number of
     elevators to be in operation on Saturdays, Sundays and holidays.

E.   Maintenance in good order, condition and repair of the parking facilities
     and all driveways leading thereto. Landlord shall keep and maintain the
     landscaped area and parking facilities in a neat and orderly condition.
     Landlord reserves the right to designate areas, in a non-discriminatory
     manner, of the appurtenant parking facilities where Tenant, its agents,
     employees and invitees shall park and may exclude Tenant and its agents,
     employees and invitees from parking in other areas as designated by
     Landlord; provided, however, Landlord shall not be liable to Tenant for the
     failure of any tenant or its invitees, employees and invitees from parking
     in other areas as designated by Landlord, provided, however, Landlord shall
     not be liable to Tenant for the failure of any tenant or its invitees,
     employees, agents or customers to abide by Landlord's designations or
     restrictions. Tenant is aware that Landlord may be required to designate
     certain parking stalls due to governmental request or order to accommodate
     car or van poolers.

Landlord acknowledges that Tenant's operations require 24-hour/day, 7/days/week
operation. As a consequence thereof, Landlord shall give to Tenant reasonable
advance notice of any planned shut downs of any Building system for scheduled
routine maintenance and/or of repairs, alterations, additions or improvements in
or to the Building Landlord shall make every effort to minimize inconvenience to
Tenant by rescheduling the times for the performance of such work upon
reasonable request of Tenant, provided that any increase in costs incurred by
Landlord as a result of such rescheduling shall be paid for by Tenant within
thirty (30) days after Tenant's receipt of Landlord's written statement and
supporting documentation.

ARTICLE 13 LANDLORD RIGHT OF ENTRY

Upon reasonable notice to Tenant, Landlord shall have access to the Premises for
purposes of showing the Premises to current or prospective lenders, to
prospective purchasers of the Project, and, during the twelve-month period
preceding the expiration of the term of this Lease, to prospective tenants
Landlord shall at all times have access to the Premises for purposes of
inspection and performing Landlord's obligations and exercising its rights under
this Lease.

ARTICLE 14 SIGNS


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<PAGE>

Tenant shall not place or permit to be placed any sign, picture, advertisement,
notice, lettering or decoration on any part of the outside of the Premises or
anywhere in the interior of the Premises which is visible from the outside of
the Premises without Landlord's prior written approval. All of Tenant's signs
shall be subject to Landlord's prior approval.

ARTICLE 15 TENANT ALTERATIONS

15.1 Tenant Alterations. Tenant may from time to time at its own expense make
changes, additions and improvements in the Premises, provided that any such
change, addition or improvement shall:

      (a) comply with the requirements of any governmental or quasi-governmental
authority having jurisdiction (including, without limitation, the Americans with
Disabilities Act), with the requirements of Landlord's insurance carriers, and
with Landlord's safety and access requirements, including restrictions on
flammable materials and elevator usage;

      (b) not be commenced until Landlord has received satisfactory evidence
that all required permits have been obtained;

      (c) be made only with the prior written consent of Landlord (which may be
withheld in Landlord's sole discretion, to the extent it relates in Landlord's
opinion to the structure or electrical, HVAC, plumbing or sprinkler systems of
the Building, but which otherwise shall not be unreasonably withheld);

      (d) be constructed in good workmanlike manner and conform to complete
working drawings prepared by a licensed architect and submitted to and approved
by Landlord;

      (e) be of a quality that equals or exceeds the then current standard for
the Project and comply with all building, fire and safety codes;

      (f) be carried out only during hours approved by Landlord by licensed
contractors selected by Tenant and approved in writing by Landlord, who shall
deliver to Landlord before commencement of the work performance and payment
bonds as well as proof of workers' compensation and general liability insurance
coverage, including coverage for completed operations and contractual liability,
with Landlord and its agents and designees named as additional insureds, in
amounts, with companies, and in form reasonably satisfactory to Landlord, which
shall remain in effect during the entire period in which the work shall be
carried out. Notwithstanding the foregoing, only subcontractors selected or
designated by Landlord may be used to make connection with the Project's main
electrical, plumbing or HVAC systems, except connections to circuit panels,
pipes or ducts within the Premises; and

      (g) upon completion, be shown on accurate "as built" reproducible drawings
in the form of reverse sepia transparencies or mylars delivered to Landlord.

15.2 Tenant Installations. Tenant may install in the Premises its usual trade
fixtures and personal property in a proper manner, provided that no installation
shall interfere with or damage the mechanical or electrical systems or the
structure of the Building. Landlord may require that any work that may affect
structural elements or mechanical, electrical, heating, air conditioning,
plumbing or other systems be performed by Landlord at Tenant's cost or by a
contractor designated by Landlord.

15.3 Mechanics Liens. Tenant shall pay before delinquency all costs for work
done or caused to be done by Tenant in the Premises which could result in any
lien or encumbrance on Landlord's interest in the Project or any part thereof,
shall keep the title to the Project and every part thereof free and clear of any
lien or encumbrance in respect of such work, and shall indemnify and hold
harmless Landlord and Landlord's agents and employees against any claim, loss,
cost, demand or legal or other expense, whether in respect of any lien or
otherwise, arising out of the supply of material, services or labor for such
work. Tenant shall immediately notify Landlord of any such lien, claim of lien
or other action of which it has or reasonably should have knowledge and that
affects the title to the Project or any part thereof, and shall cause the same
to be removed by bonding or otherwise within five days, failing which Landlord
may take such action as Landlord deems necessary to remove same and the entire
cost thereof shall be immediately due and payable by Tenant to Landlord. If
provided by applicable law, Tenant shall cause such postings to be made and
notices given as shall prevent any mechanics' lien for work done for Tenant from
attaching to the Project.

ARTICLE 16 ASSIGNMENT AND SUBLETTING

16.1 Consent Required. Tenant shall not assign its interest under this Lease or
sublet all or any part of the Premises without Landlord's prior written consent,
which shall not be unreasonably withheld. Tenant shall not at any time pledge,
hypothecate, mortgage or otherwise encumber its interest under this Lease as
security for the payment of a debt or the performance of a contract.


                                       10
<PAGE>

Tenant shall not permit its interest under this Lease to be transferred by
operation of law. Any purported assignment or sublease made without Landlord's
consent shall be void.

16.2 Requests for Approval. Landlord shall be under no obligation to decide
whether consent will be given or withheld unless Tenant has first provided to
Landlord: (a) the name and legal composition of the proposed assignee or
subtenant and the nature of its business: (b) the use to which the proposed
assignee or subtenant intends to put the Premises; (c) the terms and conditions
of the proposed assignment or sublease and of any related transaction between
Tenant and the proposed assignee or subtenant; (d) information related to the
experience, integrity and financial resources of the proposed assignee or
subtenant; (e) such information as Landlord may request to supplement, explain
or provide details of the matters submitted by Tenant pursuant to subparagraphs
(a) through (d); and (f) reimbursement for all costs incurred by Landlord,
including attorneys' fees, in connection with evaluating the request and
preparing any related documentation.

16.3 Continued Responsibility. Tenant shall remain fully liable for performance
of this Lease, notwithstanding any assignment or sublease, for the entire Lease
Term.

16.4 Excess Proceeds. If consent to an assignment or sublease is given, Tenant
shall pay to Landlord, as additional rent, all amounts received from the
assignee or subtenant in excess of the amounts otherwise payable by Tenant to
Landlord with respect to the space involved, measured on a per square foot
basis.

16.5 Limitations. Without limiting appropriate grounds for withholding consent,
it shall not be unreasonable for Landlord to withhold consent if the proposed
assignee or subtenant is a tenant in another building owned by Landlord or by an
affiliate of Landlord or of any of Landlord's constituent partners or principals
or if the use by the proposed assignee or subtenant would contravene this Lease
or any restrictive use covenant or exclusive rights granted by Landlord or if
the proposed assignee or subtenant does not intend to occupy the Premises for
its own use or if the nature of the proposed assignee or subtenant is not
compatible with the Project.

16.6 No Waiver. No consent shall constitute consent to any further assignment or
subletting.

16.7 Transfer by Landlord. Upon a sale or other transfer of the Project (or a
portion thereof containing the Premises) by Landlord, Landlord's interest in
this Lease shall automatically be transferred to the transferee, the transferee
shall automatically assume all of Landlord's obligations under this Lease
accruing from and after the date of transfer, and the transferor shall be
released of all obligations under this Lease arising after the transfer. Tenant
shall upon request attorn in writing to the transferee.

ARTICLE 17 SUBORDINATION AND ATTORNMENT

17.1 Subordination. This Lease is and shall be subject and subordinate in all
respects to all existing and future mortgages or deeds of trust now or hereafter
encumbering the Project or any part hereof. The holder of any mortgage or deed
of trust may elect to be subordinate to this Lease.

17.2 Lender Protection. Upon a transfer in connection with foreclosure or
trustee's sale proceedings or in connection with a default under an encumbrance,
whether by deed to the holder of the encumbrance in lieu of foreclosure or
otherwise, Tenant, if requested, shall in writing attorn to the transferee, but
the transferee shall not be:

      1     subject to any offsets or defenses which Tenant might have against
            Landlord; or

      2     bound by any prepayment by Tenant of more than one month's
            installment of rent;

      3     or subject to any liability or obligation of Landlord except those
            arising after the transfer.

17.3 Documentation. The subordination provisions of this Article shall be
self-operating and no further instrument shall be necessary. Nevertheless
Tenant, on request, shall execute and deliver any and all instruments further
evidencing such subordination.

17.4 Other Transactions. Landlord may' at any time and from time to time grant,
receive, dedicate, relocate, modify, surrender or otherwise deal with easements,
rights of way, restrictions, covenants, equitable servitudes or other matters
affecting the Project without notice to or consent by Tenant.

ARTICLE 18 ESTOPPEL CERTIFICATES


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<PAGE>

Tenant shall at any time within ten days after written request from Landlord
execute, acknowledge and deliver to Landlord a statement in writing: (a)
certifying that this Lease is unmodified and in full force and effect (or, if
modified, stating the nature of such modification and certifying that this
Lease, as so modified, is in full force and effect) and the date to which the
rent and other charges are paid in advance, if any; (b) confirming the
commencement and expiration dates of the term; (c) confirming the amount of the
security deposit held by Landlord; (d) acknowledging that there are not, to
Tenant's knowledge, any uncured defaults on the part of Landlord hereunder, or
specifying such defaults if any are claimed; and (e) confirming such other
matters as to which Landlord may reasonably request confirmation. Any such
statement may be conclusively relied upon by a prospective purchaser or
encumbrancer of the Premises or the Project. If Landlord desires to finance or
refinance the Project, Tenant hereby agrees to deliver to any lender designated
by Landlord such financial statements of Tenant as may be reasonably required by
such lender. Such statement shall include the past three years' financial
statements of Tenant. All such financial statements shall be received by
Landlord in confidence and shall be used only for the purposes herein set forth.

ARTICLE 19 QUIET ENJOYMENT

If Tenant pays the rent and observes and performs the terms, covenants and
conditions contained in this Lease, Tenant shall peaceably and quietly hold and
enjoy the Premises for the Term without hindrance or interruption by Landlord,
or any other person lawfully claiming by, through or under Landlord unless
otherwise permitted by the terms of this Lease. Tenant acknowledges that the
exercise by the Landlord of any of the rights conferred on Landlord under this
Lease and the entry upon the Premises for or in connection with such purposes
shall not be deemed to be a constructive or actual eviction of the Tenant and
shall not be considered to be a breach of Landlord's covenant of quiet
enjoyment.

ARTICLE 20 SURRENDER AND HOLDOVER

20.1 Surrender. Upon the expiration or termination of this Lease or of Tenant's
right to possession. Tenant shall surrender the Premises in a clean undamaged
condition and shall remove all of Tenant's equipment, fixtures and property and
repair all damage caused by the removal. Such removal shall include, without
limitation, the removal of all telephone wire located within the Premises and
from the Premises to the central telephone box for the Building. Tenant shall
not remove permanent improvements that were provided by Landlord at the
commencement of this Lease and shall not remove permanent improvements later
installed by Tenant unless directed to do so by Landlord.

20.2 Holdover. If Tenant holds over without Landlord's consent, Tenant shall, at
Landlord's election, be a tenant at will or a tenant from month-to-month. In
either case rent shall be payable monthly in advance at a rate equal to one and
one-half (150%) times the rate in effect immediately before the holdover began.
A holdover month-to-month tenancy may be terminated by either party as of the
first day of a calendar month upon at least ten days' prior notice. A holdover
tenancy at will is terminable at any time by either party without notice,
regardless of whether rent has been paid in advance. Upon a termination under
this Section, unearned rent shall be refunded following the surrender of
possession provided Tenant is not otherwise in breach of this Lease.

ARTICLE 21 BREACH. DEFAULT. AND REMEDIES

21.1 Default. The following shall constitute "Events of Default":

      (a) Tenant's failure to pay rent or any other amount due under this Lease
within five days after notice of nonpayment; or

      (b) Tenant's failure to execute, acknowledge and return a subordination
agreement under Article 17 or an estoppel certificate under Article 18 within
ten days after request; or

      (c) Tenant's failure to perform any other obligation under this Lease
within fifteen days after notice of nonperformance; provided, however, that if
the breach is of such a nature that it cannot be cured within fifteen days, no
Event of Default shall be deemed to have occurred by reason of the breach if
cure is commenced promptly and diligently pursued to completion within a period
not longer than ninety days; and provided further, that in the event of a breach
involving an imminent threat to health or safety, Landlord may in its notice of
breach reduce the period for cure to such shorter period as may be reasonable
under the circumstances; or

      (d) Tenant vacates, abandons, or otherwise ceases to use the Premises on a
substantial continuing basis except temporary absence excused by reason of fire,
casualty, failure of services or other cause wholly beyond Tenant's control; for
these purposes, absence for five consecutive business days shall conclusively be
deemed an abandonment.


                                       12
<PAGE>

21.2 Remedies. Upon the occurrence of an Event of Default, Landlord, at any time
thereafter without further notice or demand may exercise any one or more of the
following remedies concurrently or in succession:

      (a) Terminate Tenant's right to possession of the Premises by legal
process or otherwise, with or without terminating this Lease, and retake
exclusive possession of the Premises.

      (b) From time to time relet all or portions of the Premises, using
reasonable efforts to mitigate Landlord's damages. In connection with any
reletting, Landlord may relet for a period extending beyond the term of this
Lease and may make alterations or improvements to the Premises without releasing
Tenant of any liability. Upon a reletting of all or substantially all of the
Premises, Landlord shall be entitled to recover all of its then prospective
damages for the balance of the Lease Term measured by the difference between
amounts payable under this Lease and the anticipated net proceeds of reletting.

      (c) From time to time recover accrued and unpaid rent and damages arising
from Tenant's breach of the Lease, regardless of whether the Lease has been
terminated, together with applicable late charges and interest at the rate of
18% per annum or the highest lawful rate, whichever is less.

      (d) Enforce the statutory Landlord's lien on Tenant's property.

      (f) Recover all costs, expenses and attorneys' fees incurred by Landlord
in connection with enforcing this Lease, recovering possession. reletting the
Premises or collecting amounts owed, including, without limitation, costs of
alterations, brokerage commissions, and other costs incurred in connection with
any reletting.

      (g) Perform the obligation on Tenant's behalf and recover from Tenant,
upon demand, the entire amount expended by Landlord plus 20% for special
handling, supervision, and overhead.

      (h) Pursue other remedies available at law or in equity.

21.3 Subtenancies. Upon a termination of Tenant's right to possession, whether
or not this Lease is terminated: (a) subtenancies and other rights of persons
claiming under or through Tenant shall be terminated or (b) Tenant's interest in
such subleases or other arrangements shall be assigned to Landlord. Landlord may
separately elect termination or assignment with respect to each such subtenancy
or other matter.

ARTICLE 22 LANDLORD LIABILITY

Notwithstanding anything to the contrary in this Lease, neither Landlord nor
Landlord's directors, officers, shareholders, employees, agents, constituent
partners, beneficiaries, trustees, representatives, successors or assigns
(collectively, "Landlord's Affiliates") shall be personally responsible or
liable for any representation, warranty, covenant, undertaking or agreement
contained in the Lease, and the sole right and remedy of the Tenant or any
subsequent sublessee or assignee shall be against Landlord's interest in the
Project. Neither Tenant nor any subsequent sublessor or assignee shall seek to
obtain any judgment imposing personal liability against Landlord, Landlord's
Affiliates, or their successors or assigns nor execute upon any judgment or
place any lien against any property other than Landlord's interest in the
Project.

ARTICLE 23 NOTICES

Any notice from one party to the other shall be in writing and shall be deemed
duly served: (a) if delivered personally to a responsible employee of Tenant, if
sent by facsimile with receipt acknowledged, or if mailed by registered or
certified mail addressed to Tenant at the Premises or (b) if mailed by
registered or certified mail to Landlord at the address set forth in Section 1.
15 or such other address as Landlord may designate. Any notice to Tenant prior
to Tenant's taking possession of the Premises, however, shall instead be sent to
the address set forth in Section 1.14. Any notice shall be deemed to have been
given when mailed, if mailed, when faxed, if faxed, and when delivered, if
personally delivered.


                                       13
<PAGE>

ARTICLE 24 BROKERAGE

Tenant warrants and represents that no broker or other person is entitled to
claim a commission, broker's fee or other compensation in connection with this
Lease except: (i) brokers or other persons that Landlord may have retained or
employed directly, and (ii) brokers whom Tenant has previously specifically
designated in writing to Landlord as Tenant's representative as listed in
Section 1.16. Tenant shall defend, indemnify and hold Landlord harmless from all
claims or liabilities arising from any breach of the foregoing representation
and warranty.

ARTICLE 25 RELOCATION

      INTENTIONALLY DELETED

ARTICLE 26 GENERAL

26.1 Severability. If any term, covenant or condition of this Lease, or the
application thereof, is to any extent held or rendered invalid, it shall be and
is hereby deemed to be independent of the remainder of the Lease and to be
severable and divisible therefrom, and its invalidity, unenforceability or
illegality shall not affect, impair or invalidate the remainder of the Lease or
any part thereof.

26.2 No Waiver, The waiver by Landlord of any breach of any term, covenant or
condition contained in this Lease shall not be deemed to be a waiver of such
term, covenant or condition or of any subsequent breach of the same or of any
other term, covenant or condition contained in this Lease. The subsequent
acceptance of rent by Landlord shall not be deemed to be a waiver of any
preceding breach by Tenant of any term, covenant or condition of this Lease,
regardless of Landlord's knowledge of such preceding breach at the time of
acceptance of rent. No term, covenant or condition of this Lease shall be deemed
to have been waived by Landlord unless such waiver is in writing by Landlord.

26.3 Effect of Payment. No payment by Tenant or receipt by Landlord of a lesser
amount than the monthly payment of rent herein stipulated is deemed to be other
than on account of the earliest stipulated rent, nor is any endorsement or
statement on any check or any letter accompanying any check or payment of rent
deemed an acknowledgment of full payment or accord and satisfaction, and
Landlord may accept and cash any check or payment without prejudice to
Landlord's right to recover the balance of the rent due and pursue any other
remedy provided in this Lease.

      26.4 Delay. If either party is delayed or hindered in or prevented from
      the performance of any term, covenant or act required hereunder by reasons
      of strikes, labor troubles, inability to procure materials or services,
      power failure, restrictive governmental laws or regulations, riots,
      insurrection, sabotage, rebellion, war, act of God, or other reason
      whether of a like nature or not that is beyond the control of the party
      affected, financial inability excepted, then the performance of that term,
      covenant or act is excused for the period of the delay and the party
      delayed shall be entitled to perform such term, covenant or act within the
      appropriate time period after the expiration of the period of such delay.
      Nothing in this Section, however, shall excuse Tenant from the prompt
      payment of any amount payable under this Lease nor from the consequences
      of Tenant Delay as provided in Exhibit C (if attached).

      26.5 Lender Notice, In the event of a material default by Landlord of a
      sufficiently serious nature that Tenant considers the utility of the
      Premises to Tenant to be significantly impaired, Tenant shall give written
      notice of the default to Landlord and shall simultaneously send a copy of
      the notice to the holder of any encumbrance, the name and address of whom
      has previously been furnished in writing to Tenant. If Landlord fails to
      cure the default within a reasonable time, Tenant shall send a second
      notice to that effect to the holder of the encumbrance, with a copy to
      Landlord, and the holder of the encumbrance then shall have a reasonable
      time, not less than thirty days, to cause the default to be remedied.

      26.6 No Offer. The submission of this Lease for examination does not
      constitute a reservation of an option to lease the Premises, and this
      Lease becomes effective as a lease only upon its execution and delivery by
      Landlord and Tenant.

      26.7 Successors. All rights and liabilities under this Lease extend to and
      bind the successors and assigns of Landlord and permitted successors and
      assigns of Tenant. No rights, however, shall inure to the benefit of any
      transferee of the Tenant unless the transfer has been consented to by the
      Landlord in writing as provided in Section 16.1. If there is more than one
      Tenant, they are all bound jointly and severally by the terms, covenants
      and conditions of this Lease.


                                       14
<PAGE>

26.8 Integration. This Lease and the Exhibits hereto attached, set forth all the
covenants, promises, agreements, conditions and understandings between Landlord
and Tenant concerning the Premises and there are no other covenants, promises,
agreements, conditions or understandings, either oral or written, between them.
No alteration, amendment or addition to this Lease shall be binding upon
Landlord or Tenant unless in writing and signed by Tenant and Landlord.

26.9 WAIVER OF JURY TRIAL. IN ANY LITIGATION BETWEEN LANDLORD AND TENANT, THE
MATTER SHALL BE DECIDED BY A JUDGE SITTING WITHOUT A JURY, AND TENANT
ACCORDINGLY WAIVES ITS RIGHT TO A JURY TRIAL.

26.10 Governing Law. This Lease shall be construed in accordance with and
governed by the laws of the State of Arizona.

26.11 Deadlines Enforceable. Time is of the essence of this Lease and of every
part hereof

26.12 Counterparts. This Lease may be executed in counterparts, which together
shall constitute a single instrument.

26.13 Additional Provisions:

      1. Tenant's Option to Renew

            (A)   Provided that this Lease is then in full force and effect and
                  Tenant is not in default, on the date of exercise of this
                  Option, hereunder after notice and the expiration of any
                  applicable grace period, Tenant shall have the option to
                  extend the Term for two (2) additional periods of five (5)
                  years each (the "Extension Term(s)"). The Extension Term(s)
                  shall commence on the day after the initial Lease term and the
                  prior Extension Term (if any) expires ("Expiration Date(s)")
                  and shall expire on the fifth (5th) anniversary of the
                  Expiration Date(s) unless the Extension Term(s) shall sooner
                  end pursuant to this Lease.

            (B)   The terms and conditions shall be identical to those in the
                  primary lease except for the rental rate, which shall be the
                  market rental rate determined by Landlord and Tenant based on
                  the rental rate allowances and concessions for comparable
                  buildings in the same immediate geographic area. Landlord
                  shall provide Tenant a proposed rental rate at least nine (9)
                  months but not more than twelve (12) months prior to the
                  termination of the Lease term. Tenant will accept/reject such
                  offer no less than six (6) months prior to the termination of
                  the Lease. If Landlord and Tenant are unable to agree on a
                  market rental rate, allowances and concessions, each shall
                  hire a licensed commercial real estate broker with at least
                  ten (10) years of experience in the local commercial real
                  estate market and those brokers will hire a third licensed
                  commercial real estate broker with the same experience in the
                  local commercial real estate market to all determine a market
                  rate, allowances and concessions. The average rate, allowances
                  and concessions determined by these three (3) brokers will be
                  considered the market rental rate and improvement allowance
                  for the purposes of the Renewal Option.

            (C)   Promptly after the rent has been determined, Landlord and
                  Tenant shall execute, acknowledge and deliver an agreement
                  setting forth the rent for the Extension Term(s). as finally
                  determined, provided that the failure of the parties to do so
                  shall not affect their respective rights and obligations under
                  the Lease.

Nowithstanding any provisions in Sections 1-26 of the Lease, Landlord and Tenant
hereby agree as follows:


                                       15
<PAGE>

27.   Services.

      A.    Landlord's Obligations. Landlord shall use all reasonable efforts to
            furnish to Tenant (I) water at those points of supply provided for
            general use of tenants of the Building in the common areas thereof;
            (2) heated and refrigerated air conditioning ("HVAC") as appropriate
            to the common areas of the Building, at such temperatures and in
            such amounts as are standard for comparable buildings in the
            vicinity of the Building; (3) janitorial service to the common areas
            of the Building on weekdays, other than holidays, for
            Building-standard installations and such window washing as may from
            time to time be reasonably required; and (4) elevator(s) for ingress
            and egress to the floor on which the Premises are located, in common
            with other tenants, provided that Landlord may reasonably limit the
            number of operating elevators during non-business hours and
            holidays. Landlord shall maintain the common areas of the Building
            in reasonably good order and condition.

      B.    Electrical Service. All electrical power for the Premises and for
            the operation of Tenant's equipment shall be submetered by Landlord,
            and be furnished, installed and maintained at Tenant's sole expense.
            Without limiting the generality of the foregoing, Tenant, at its
            sole cost and expense, shall pay the cost of all equipment, meters,
            switches, transformers, feeders, risers, and wiring required to
            provide electrical service to the Premises. The installation of all
            electrical equipment shall be done only in substantial accordance
            with plans and specifications that have been previously submitted to
            and approved by Landlord in writing. Whenever Tenant is required to
            pay' the cost of any electrical equipment under the foregoing
            provisions, the cost thereof shall include the cost of installation,
            operation, use and maintenance of such electrical equipment. If
            electrical service to the Premises is submetered, the submeter shall
            be read by Landlord and Tenant shall pay to Landlord, within ten
            (10) days after Tenant's receipt of an invoice therefore the actual
            cost of such electrical service based on rates charged for such
            service by the utility company furnishing such service, including
            all fuel adjustment charges, demand charges and taxes.

      C.    Restoration of Services/Tenant Self-Help Remedy. Landlord shall use
            good faith best efforts to restore any service described in Section
            27(a) that becomes unavailable interrupted, discontinued or
            insufficient; however, such unavailability shall not render Landlord
            liable for any damages caused thereby, be a constructive eviction of
            Tenant, constitute a breach of any implied warranty, or, except as
            provided in the next sentence, entitle Tenant to any abatement of
            Tenant's obligations hereunder. If, however, Tenant is prevented
            from using the Premises for more than 4 consecutive business days
            because of the unavailability of any such service, then Tenant
            shall, as its exclusive remedy be entitled to a reasonable abatement
            of Rent for each consecutive day that Tenant is so prevented from
            using the Premises. Tenant Self-Help Remedy: if the Landlord shall
            fail to restore said service within five (5) days of its
            interruption, then Tenant may make perform such obligation and
            offset the amount of the reasonable cost of such performance against
            any base rent, additional rent or any other amounts payable be
            Tenant under this Lease.

D. Generator & HVAC Access. Landlord will install its own generator system,
Tenant shall be granted the right to purchase up to 500 KW of power from the
Building's generator based on the initial fee and monthly charges specified
below. Tenant shall have the right to install a minimum of 2-4" conduits to
connect the Premises to the generator power connection point. Tenant shall have
the right to utilize up to 60 tons of capacity from the Building's chilled water
system based on the monthly charges specified below. Landlord shall "stub" the
chilled water lines to a mutually determined location. Landlord shall provide
chilled water at approximately 55 degrees fahrenheit, and such chilled water
shall be provided 24 hours a day/7 days a week/365 days a year throughout the
Term of the Lease. Landlord shall use all possible efforts to ensure that the
chilled water is provided to Tenant continuously, and at the correct
temperature. Tenant shall have the right to review the maintenance procedures of
the generator and chilled water system and shall have the periodic right to
review such records.

      Generator/HVAC Fees:
<PAGE>

            Initial charge: $175,000.00

            Monthly access: $1,500.00

            Monthly fuel service: Proportionate share of actual fuel costs

      THE FOLLOWING SECTIONS (28-35) ALL REQUIRE AND ARE SUBJECT TO LANDLORD'S
      PRIOR WRITTEN APPROVAL. SAID APPROVAL WILL NOT BE UNREASONABLY WITHHELD,
      CONDITIONED, OR DELAYED.

      28.   Risers & Conduit Access Landlord shall provide Tenant with rights to
            install four (4) four-inch (4") conduits ("Main Conduit") which
            shall run from the Basement to the Premises and which shall run the
            entire length of the building to connect Tenant's telecommunications
            facility to other tenants in the building and to connect to the
            point of entry or "hand off point/meet me room" in the building for
            all fiber carriers. Tenant shall also have the right to run feeder
            conduit stemming from the Main Conduit to connect each tenant on
            each floor of the building. All conduit will be installed at
            Tenant's sole cost and Landlord shall not charge any fees for said
            conduit access.

      29.   Battery Installation Tenant shall have the right to install wet cell
            batteries with the necessary seismic racks and spill containment.

      30.   Grounding Riser Tenant, at no additional rental cost, shall have the
            right to install a separate electrical ground and/or tie into the
            Building's primary ground system in accordance with equipment
            requirements and applicable laws.

      31. Antennae

            (a)   Tenant shall have the right to install a GPS antenna in a
                  location to be mutually agreed upon by both Landlord and
                  Tenant. Tenant shall be granted sufficient conduit space for
                  such installation and not be charged for such conduit or roof
                  space.

            (b)   Tenant shall be granted access to the roof 24 hours per day
                  via escort by a Building engineer or security guard. During
                  normal business hours, Landlord shall make arrangements for
                  immediate access and after normal business hours and on
                  weekends, Landlord shall provide a telephone number for Tenant
                  to contact to arrange immediate access.

32.   Fire Protection & Life Safety. Tenant shall have the right to convert any
      existing sprinkler system or install a preaction or FM 200 system. Tenant
      shall install such system subject to local codes and ordinances.

33.   Hazardous Substances To the best of Landlord's knowledge, no part of the
      Premises or the Building including without limitation, the walls,
      ceilings, structural steel, flooring, pipes or boilers, is wrapped,
<PAGE>

      insulated, fireproofed or surfaced with any asbestos-containing materials.
      Landlord shall provide the Premises and all other areas of the Premises
      where Tenant places equipment free of hazardous materials.

34.   Express Waiver of Landlord's Lien. Landlord hereby expressly waives its
      Landlord's lien and any and all rights granted by or under any present or
      future laws to levy or distrain for rent, in arrears, in advance, or both,
      upon any or all personalty, including, but not limited to [supporting
      towers, antennas, satellite dish(es), Connecting Equipment] equipment,
      trade fixtures, furniture and other personal property of Tenant or any
      assignee or subtenant of Tenant in the Premises.

35.   Allowable Use of Certain Hazardous Materials. Tenant may use and store the
      following materials in the ordinary course of its business: fuel for the
      generator(s) in order to supply an uninterrupted power source (UPS); acid
      contained within batteries for back-up power; reasonable amounts of
      standard cleaning fluid and materials customarily used in conjunction with
      business machines; cleaning supplies in reasonable quantities; coolant for
      any Tenant installed HVAC system, or other materials used in fire
      suppression and any other materials deemed necessary to Tenant's business.
      Landlord may use, but not store, on the Premises the following materials
      in the ordinary course of business: cleaning supplies, insecticides,
      fungicides, and rodenticides. Tenant shall not indemnify Landlord for
      releases of any hazardous materials that exist on the Premises at the time
      of execution of this Lease or are brought on the Premises, into the
      building, or on, in or under the land upon which the Building is located
      by anyone other than Tenant, its employees, agents, or third-party
      contractors. This provision shall survive the expiration or sooner
      termination of this Lease.


                                  TENANT:  Advanced Telecommunications Inc.
                                           A Delaware corp.


                                      By: _________________________________

                                      Its: ________________________________

                                      Date _____________________________________


                                  LANDLORD:

                                      SOFI-IV SIM OFFICE INVESTORS II, LP, an
                                      Delaware limited partnership

                                      By:   Scottsdale Property Management 97,
                                            L.L.C., an Arizona limited liability
                                            company, Agent


                                            By _________________________________
                                               Authorized signatory

                                      Date______________________________________
<PAGE>


                                    EXHIBIT A

                                  THE PREMISES


                                       A-1
<PAGE>

                                   EXHIBIT A-1

                                   FLOOR PLAN


                                       A-2
<PAGE>

                                    EXHIBIT B

                             CONSTRUCTION PROVISIONS

1 Preliminary Space Plan. Attached to this Lease as Exhibit A is a preliminary
space plan approved by Landlord and Tenant showing the size, nature and location
of the improvements to be constructed in the Premises (the "Improvements").
Promptly following execution of this Lease, Tenant shall meet with Landlord's
architect and shall provide such information and make such selections as may be
necessary for the expeditious completion of the planning process.

2 Working Drawings. Based upon the preliminary space plan and the information
provided and selections made by Tenant, Landlord shall cause working drawings
and specifications (collectively, the "Plans") to be prepared for the
Improvements. The Plans shall be subject to Tenant's reasonable approval. Tenant
shall respond with all of its specific objections or comments to the proposed
Plans within five days after receipt, and the Plans shall be modified to satisfy
any reasonable objection of Tenant. Tenant shall promptly give its written
approval of the revised Plans or indicate specific changes required to be made.
Any revisions of the Plans after the revisions to the initial draft of the
proposed Plans shall be made at Tenant's sole expense, payable on demand.

3 Cooperation, During the entire course of the process described above, both
Landlord and Tenant shall review and respond to submissions by the other party
with reasonable dispatch. Tenant shall respond with its approval or comments
within five days after receipt of initial drawings, specifications, or other
materials requiring Tenant's review and within three days after receipt of
revised versions of such documents or materials. From time to time at the
request of either party Landlord and Tenant shall devise, and revise as
necessary, working schedules for the preparation of the Plans and the
construction of the Improvements. Tenant shall not permit any supplier,
installer, contractor, or other person employed by Tenant to interfere in any
way with the progress of the work. Access by Tenant's suppliers, contractors and
installers shall be subject to (i) scheduling by Landlord upon at least ten
days' prior notice by Tenant, and (ii) compliance with all requirements imposed
by Landlord with respect to insurance, cooperation, permits, licenses, bonding,
hours of work, safety and use of flammable substances.

4 Redesign Option. If after the Plans are completed and Landlord's contractor
has submitted a price for the work, the estimated costs of construction exceed
the Tenant Improvement Allowance, Tenant may elect within three days after
receipt of the cost estimate to attempt to reduce the associated cost by
reducing the scope of the work to be done. The changes, which shall be subject
to Landlord's prior approval, shall be incorporated in revised Plans. Any
redesign and rebidding shall be completed within seven days after receipt of the
initial cost estimate.

5 Cost. Prior to commencement of construction, Tenant shall pay to Landlord the
amount, if any, by which the estimated costs of construction exceed the Tenant
Improvement Allowance as set forth in Section 1.13. Any difference between
actual and estimated costs shall be paid or refunded, as the case may be, within
ten days after receipt of Landlord's statement calculating the amount due.
Landlord shall prepare and deliver the statement within a reasonable time after
completion of punchlist items. "Costs of construction" of the Improvements as
used in this Article means all costs and expenses incurred to design and build
the improvements, including, without limitation, permit and inspection fees,
management and supervision fees, taxes, amounts paid to contractors,
subcontractors, and suppliers, architects' fees, engineering costs, premiums for
bonds and insurance, utilities, equipment rental, demolition, labor, materials,
and supplies.

6 Punchlist. Within ten days after taking possession of the Premises, Tenant
shall deliver to Landlord a written punchlist specifying all defects in
materials or workmanship in the Improvements. Any defects not specified in the
punchlist, except latent defects not readily discoverable by inspection, are
waived. Landlord shall promptly cause all matters appearing on the punchlist to
be corrected.

7 Delay. If completion of construction of improvements within the Premises or
delivery of possession of the Premises is delayed by Tenant Delay, then the
Commencement Date shall be deemed to have occurred and rent shall begin to
accrue as of the date when they would have done so but for the Tenant Delay.
"Tenant Delay" means delay as a result of: (a) Tenant's failure to meet with the
architect and to provide all required information and make necessary selections
for the expeditious development of Plans; (b) Tenant's failure to provide
comments on proposed Plans in a timely manner; (c) Tenant's request for
materials, finishes or installations requiring more time to obtain, construct or
install than Landlord's standard; or (d) Tenant's change in any Plans after the
revisions to the initial draft; or, (e) performance or completion by a party
employed by Tenant. Landlord shall not be liable for any direct or consequential
damages resulting from delayed delivery of the Premises (by reason of delayed
construction, failure or refusal of a prior tenant of the space to vacate the
Premises in accordance with its lease, or otherwise) and the scheduled
Commencement Date and the Expiration Date shall be postponed by an amount equal
to the period of delay.


                                       C-1
<PAGE>

                                    EXHIBIT C

                              RULES AND REGULATIONS

1 Any sign, lettering, picture, notice or advertisement installed within
Lessee's premises which is visible to the public from within the Building shall
be installed at Tenant's cost and in such manner, character and style as
Landlord may approve in writing. No sign, lettering, picture, notice or
advertisement shall be placed on any outside window or in a position to be
visible from outside the Building. Any object violating this paragraph may be
removed by Landlord, at Tenant's expense.

      2 In advertising or other publicity, without Landlord's prior written
consent, Tenant shall use neither the name of the Building, except as the
address of its business, nor pictures of the Building.

      3 Tenant, its customers, invitees, licensees and guests shall not obstruct
the sidewalks, entrances, passages, courts, corridors, vestibules, halls,
elevators or stairways of the Building. The sashes, sash doors, skylights,
windows and doors that reflect or admit light and air into lobbies, halls,
passageways or other public places in the Building shall not be covered or
obstructed. Tenant shall not place objects against glass partitions or doors or
windows which would be unsightly from Building corridors, lobbies, passageways,
or other public places, or from the exterior of the Building, and will promptly
remove same upon notice from Landlord. This provision does not apply to window
coverings, chosen by Tenant and approved by Landlord.

      4 Tenant shall not make noises, cause disturbances or vibrations, or use
or operate any electrical or electronic device or other device that emits sound
or other waves or disturbances, any of which may be offensive to other tenants
and occupants of the Building or which may interfere with the operation of any
device or equipment or radio or television broadcasting or reception from or
within the Building or elsewhere, and shall not place or install any
projections, antennae, aerials or similar devices inside or outside of the
Premises.

      5 Tenant shall not make any room-to-room canvass to solicit business from
other tenants in the Building and shall not exhibit, sell or offer to sell, use,
rent or exchange any item or service in or from the Premises unless ordinarily
embraced within Tenant's use of the Premises specified in the Lease.

      6 Tenant shall not waste electricity or water and agrees to cooperate
fully with Landlord to assure the most effective operation of the Building's
heating and air conditioning and shall refrain from attempting to adjust any
controls other than room thermostats installed for Tenant's use. Tenant shall
keep windows and public corridor doors closed.

      7 Door keys, not to exceed two, for doors in the Premises will be
furnished at the commencement of the Lease by Landlord. Tenant shall not fix
additional locks on doors and shall purchase duplicate keys only from Landlord
at Tenant's expense. When the Lease is terminated, Tenant shall return all keys
to Landlord and will disclose to Landlord the combination of any safes, cabinets
or vaults left in the Premises.

      8 Tenant assumes full responsibility for protecting its space from theft,
robbery and pilferage. Such protection shall include keeping doors locked where
appropriate and other means of entry to the Premises closed and secured.

      9 Peddlers, solicitors and beggars shall be reported to Landlord or as
Landlord otherwise requests.

      10 Tenant shall not install or operate machinery or any mechanical device
of a nature not directly related to Tenant's ordinary use of the Premises as
general office space without the written permission of Landlord. Wherever
heat-generating machines or equipment are used in the Premises which affect the
temperature otherwise maintained by the air conditioning system, Landlord
reserves the right to install supplementary air conditioning units to cool the
Premises, and Tenant shall pay to Landlord upon demand the cost thereof,
including the cost of installation, operation and maintenance. Tenant will not,
without Landlord's prior written consent, use any apparatus or device using
electric current in excess of 110 volts, or which increases the amount of
electricity, water or other utility otherwise furnished or supplied for use of
the Premises as general office space, nor connect to the electric current or the
water supply except through existing electrical outlets or water taps in the
Premises. If Tenant requires water, electric current or other utilities in
excess of those otherwise furnished for use of the Lease Premises as general
office space, Tenant shall first procure Landlord's written consent to the use
thereof, which consent Landlord may refuse for any reason, and Landlord may
cause metering devices to be installed in the Premises or Building for the
purpose of measuring the amount of water, electric current or other utilities
consumed for any such purpose. Tenant shall pay to Landlord upon demand the cost
of any such meters and the installation, maintenance and repair thereof and the
cost of all water, electric current or other utilities consumed as shown by said
meters, at the rates charged for such services by the suppliers thereof.


                                       D-1
<PAGE>

      11 No person or contractor not employed or approved by Landlord shall be
used to perform window washing, cleaning, decorating, repair or other work in
the Premises, Building or Project.

      12 In no event shall any person bring into the Project inflammables, such
as gasoline, kerosene, naphtha and benzene, or explosives, or any other article
of intrinsically dangerous nature. If by reason of the failure of Tenant to
comply with the provisions of this paragraph, any insurance premium payable by
Landlord for all or any part of the Project shall at any time be increased above
normal insurance premiums for insurance not covering the items aforesaid,
Landlord shall have the option to resort to one or more of the following:
terminate this Lease, require Tenant to make immediate payment for the whole of
the increased insurance premium and exercise any other remedy or combination of
remedies set forth in the Lease.

      13 Water, toilet and other plumbing fixtures shall not be used for any
purpose other than those for which they were constructed, and no sweeping,
rubbish, rags or other substance shall be thrown therein. All damage resulting
from any misuse of said fixtures by Tenant or its servants, employees, agents,
visitors or licensees shall be borne by Tenant.

      14 Tenant shall not mark, paint, drill into or in any way de face any part
of the Premises or the Building. No boring, cutting or stringing of wires or
laying of linoleum or other similar floor covering shall be permitted except
with the prior written consent of Landlord and as Landlord may direct.

      15 Except with Landlord's prior written consent, no bicycles, similar
vehicles or animals of any kind shall be brought into or kept in or about the
Premises or Project. Except for a tenant whose business in the Building is the
preparation of food for on-premises public sale and consumption, no cooking
shall be done or permitted by Tenant in the Building except that the use of
microwave ovens for the warming of prepared foods and the preparation of coffee,
tea, hot chocolate and similar items for Tenant and its employees, clients and
guests shall be permitted. Tenant shall not cause or permit any unusual or
objectionable odors to be produced or permeate the Project, Building or
Premises.

      16 The Premises shall not be used for manufacturing or for the storage of
merchandise except such storage as may be incidental to the use of the Premises
for general office purposes and any additional use specifically set forth in the
Lease. Tenant shall not occupy or permit any portion of the Premises to be
occupied as an office for a public stenographer or typist or for the manufacture
or sale of liquor, narcotics or tobacco in any form or as a medical office or as
a barber or manicure shop or as an employment bureau. Tenant shall not engage or
pay any employees on the Premises except those actually working for Tenant on
the Premises, or advertise for laborers giving an address at the Premises. The
Premises shall not be used for lodging or sleeping or for any immoral or illegal
purposes.

      17 There shall not be used by Tenant in any space or in the public halls
of the Building any hand trucks except those equipped with rubber tires and side
guards.

      18 Tenant shall not conduct any auction or permit any fine or bankruptcy
sale to be held in the Premises or store goods, wares or merchandise in the
Premises or at the Project.

      19 All freight, furniture and equipment must be moved into, within and out
of the Building under Landlord's supervision and according to such regulations
as Landlord may promulgate. All moving of freight, furniture or equipment into
or out of the Building by Tenant shall be done at such time and in such manner
as directed by Landlord or its agent. Landlord shall have the right to prescribe
the allowable weight, size, and placement details for all sales and other heavy
equipment brought into the Building. Landlord will not be responsible for loss
of, or damage to, any such safe or property from any cause, and all damage done
to the Building by moving or maintaining any such property shall be repaired at
the expense of Tenant. No office equipment, furnishings or fixtures shall be
removed from the Building during hours when the Building is closed without
obtaining Landlord's prior written permission and Landlord's security personnel
shall have the right to demand evidence of such permission from any person.

      20 Requirements of Tenant for building services, maintenance and repairs
shall be attended to only upon application to Landlord. Employees of the
Building are not permitted to perform any work or do anything outside of their
regular duties unless under special instructions from Landlord. No employees of
the Building shall admit any person, Tenant or otherwise, to any office without
specific instructions from Landlord.

      21 Tenant shall promptly notify Landlord of any accidents to or defects in
plumbing, electrical fixtures, heating apparatus and/or air conditioning
equipment so that the same may be attended to properly.

      22 Landlord reserves the right to close and keep locked all entrance and
exit doors of the Project at all times which are not ordinary business hours.
For purposes of this paragraph, "Ordinary business hours" in the Building shall
be from 7:00 a.m. to 6:00 p.m. on Mondays through Fridays but excluding any day
which is a legal holiday.


                                       D-2
<PAGE>

      23 On Saturdays, Sundays, legal holidays and other days during the hours
the Building may be closed after ordinary business hours, access to the Project
or Building or to the halls, corridors, elevators or stairways will be
controlled by Landlord through the use of security personnel or access cards.
Such personnel will have the right to demand of any and all personal seeking
access to the Building proper identification to determine if they have right of
access to the Project. Landlord shall in no case be liable for damages wherein
admission to the Building has been refused during the hours the Building may be
closed after ordinary business hours by reason of a tenant's failing to properly
identify himself or herself to the security personnel, or because the Building
was locked and closed to access by a tenant, a tenant's employees and the
general public.

      24 A directory in the main lobby of the Building shall be provided to
display the name and location of Building tenants only. Landlord reserves the
right to exclude any other name therefrom and also to make a reasonable charge
for each name, in addition to Tenant's name, placed upon such directory at
Tenant's request.

      25 Tenant shall not be entitled, by virtue of this Lease, to use or
patronize any service, business or facility located in the Building, but may
become entitled to use or patronize the same by satisfactory arrangements with,
and subject to all of the terms and conditions imposed by, the operator of such
business or facility.

      26 Landlord reserves the right to exclude or expel from the Building any
person who, in the Landlord's judgment, is intoxicated or under the influence of
liquor or drugs, or who shall in any manner violate any of the rules and
regulations contained herein.

      27 Landlord reserves the right at any time and from time to time to waive
any of the Building rules and regulations.

      28. There shall be no smoking anywhere in the Building. Tenant shall
cooperate with Landlord and landlord's agents to enforce this rule.


                                       D-3
<PAGE>



                                       F-4
<PAGE>

      insulated, fireproofed or surfaced with any asbestos-containing materials.
      Landlord shall provide the Premises arid all other areas of the Premises
      where Tenant places equipment free of hazardous materials

34.   Express Waiver of Landlord's Lien. Landlord hereby expressly waives its
      Landlord's lien and any and all rights granted by or under any present or
      future laws to Levy or distrain for rent, in arrears, in advance, or both,
      upon any or all personalty, including, but not limited to [supporting
      towers, antennas, satellite dish(es). Connecting Equipment] equipment,
      trade fixtures, furniture and other personal property at Tenant or any
      assignee or subtenant of Tenant in the Premises.

35.   Allowable Use of Certain Hazardous Materials. Tenant may use and store the
      following materials in the ordinary course of its business: fuel for the
      generator(s) in order to supply an uninterrupted power source (UPS); acid
      contained within batteries for back-up power; reasonable amounts of
      standard cleaning fluid and materials customarily used in conjunction with
      business machines; cleaning supplies in reasonable quantities; coolant for
      any Tenant installed HVAC system, or other materials used in fire
      suppression and any other materials deemed necessary to Tenant's business.
      Landlord may use, but not store, art the Premises the following materials
      in the ordinary course of business: cleaning supplies, insecticides,
      fungicides, and rodenticides. Tenant shall not indemnify Landlord for
      releases of any hazardous materials that exist on the Premises, at the
      time of execution of this Lease or are brought on the Premises, into the
      building, or on, in or under the land upon which the Building is located
      by anyone other than Tenant, its employees, agents, or third-party
      contractors. This provision shall survive the expiration or sooner
      termination of this Lease.



                                  TENANT:  Advanced Telecommunications Inc.
                                           A Delaware corp.


                                      By: /s/ S. C. Tivari
        SATISH C. TIVARI                  ---------------------------------
      V.P. ENGINEERING AND
     NETWORK IMPLEMENTATION           Its:
ADVANCED TELECOMMUNICATIONS, INC.         ---------------------------------
    720 2ND AVE S. SUITE 1200
      MINNEAPOLIS, MN 55402           Date     12/27/99
                                           -------------------------------------

                                  LANDLORD:

                                      SOFI-IV SIM OFFICE INVESTORS II, LP, an
                                      Delaware limited partnership

                                      By:   Scottsdale Property Management 97,
                                            L.L.C., an Arizona limited liability
                                            company, Agent


                                            By /s/ [ILLEGIBLE]
                                               ---------------------------------
                                               Authorized signatory

                                      Date     12-30-99
                                           -------------------------------------

Subject to Landlord's
Receipt of:

-- Security deposit

-- 1st Month's Rent

-- Generator/HVAC Fee