Document:

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                                                                   Exhibit 10.20

                             OFFICE LEASE AGREEMENT

STATE OF TEXAS

COUNTY OF DALLAS

      THIS LEASE AGREEMENT made and entered into as of the 14th day of November
2000, by and between the Landlord and Tenant hereinafter named.

                              W I T N E S S E T H:

      1. Definitions and Basic Provisions. The following definitions and basic
provisions shall, be used in conjunction with and limited by the reference
thereto in the provisions of this lease:

      (a)   "Landlord":    TR Lookout Partners, Ltd.

      (b)   "Tenant":      telecom technologies, inc.

      (c)   "Premises":    Lookout Plaza Phase I
                           1301 E. Lookout Drive, Suite 3000
                           Richardson Texas 75080

as generally outlined on the plan attached hereto as Exhibit "A." The term
"rentable area" as used herein, shall refer to the sum of (a) the entire area
included within the Premises, being the area bounded by the Interior of the
exterior wall or walls of the Building, the exterior of all walls separating the
Premises from any public corridors or other public areas, and, for multi-tenant
floors, the centerline of all walls separating the Premises from other areas
leased or to be leased to other tenants, plus (b) a pro rata portion (or all, in
the case of a single tenant floor) of the, area covered by the elevator lobbies,
columns, projections, vertical penetrations, other structural portions, other
common areas, and other service areas situated on such floor. Upon completion of
the leasehold improvements described on attached Exhibit "C", the rentable area
of the Premises shall be measured by Landlord's architect in accordance with the
BOMA method hereafter set forth. The rentable area of the Premises shall be
calculated in accordance with the methods of measuring rentable areas described
in the standard method for measuring floor area in office buildings, ANSI
Z65.1-1996, as promulgated by the Building Owners and Managers Association
(BOMA) International. The estimates of rentable area within the Premises and
within the Building as set forth herein shall be revised if Landlord's architect
determines such estimate to be inaccurate, or if there is a change after the
"Commencement Date" (hereinafter defined) in either the rentable area of the
Premises or the Building, and the terms of this lease shall be adjusted
accordingly. The rentable area in the leased Premises has been estimated on the
basis of the foregoing definition to be 109,966 square feet of rentable area.
The Premises are divided into two (2) portions, approximately 91,684 square feet
of rentable area (the "First Portion") outlined on the plan attached hereto as
Exhibit "A", and approximately 18,282 square feet of rentable area (the Second
Portion") also outlined on the plan attached hereto as Exhibit "A." Landlord and
Tenant both agree to the following occupancy and takedown schedule: On September
1, 2001 Tenant will occupy the First Portion; and on September 1, 2003, Tenant
will occupy the Second Portion. Notwithstanding the foregoing, in the event
Tenant occupies the Second Portion prior to September 1, 2003, paragraphs "(e)"
and "(f)" below shall be modified so that the basic rental and the monthly
rental installment reflect the revised occupancy date for the Second Portion. In
no event will the occupancy date for the Second Portion be later than September
1, 2003. Each of the above occupancy dates shall be subject to Substantial
Completion (as defined herein) with respect to the tenant improvements regarding
such portion. Any delay in completion of such tenant improvements shall delay
Tenant's obligation to occupy such space. The total rentable area of the
Building is estimated for all purposes herein to be 155,092 square feet.

      (d)   Lease term: A period of 84 months, commencing on September 1, 2001
            (the "Commencement Date") and ending on August 31, 2008.

      (e)   Basic rental: $14,902,174.00.

      (f)   Monthly rental installment:

<TABLE>
<CAPTION>
            Time Period                        Rentable Area   Monthly Rental    Annual Rental Rate
                                                                 Installment       Per Square Foot
            <S>                                    <C>           <C>                   <C>
            Monthly from September 1, 2001
            through August 31, 2003                 91,684       $148,986.50           $19.50

            Monthly from September 1, 2003
            through August 31, 2006                109,966       $178,694.75           $19.50

            Monthly from September 1, 2006         109,966       $203,876.96           $22.25
            through August 31, 2008
</TABLE>

      (g)   Security deposit: $0.00

      (h)   Permitted use: Office, including laboratory and testing facilities,
but specifically excluding the practice of law (in the event Haynes and Boone is
a tenant in the Building) except for Tenant's "in-house" attorneys.

      (i)   "Land":     The real property upon which the Project is located,
                        described more particularly on "Exhibit E" attached
                        hereto and made a part hereof.

      (j)   "Building": Lookout Plaza Phase I located at 1301 E. Lookout Drive,
                        Richardson, Texas 75080.

      (k)   "Project":  Lookout Plaza located at 1301 E. Lookout Drive,
                        Richardson, Texas 75080.

      2. Lease Grant. Before the Commencement Date, Landlord shall construct the
Building and install in the First Portion of the Premises the items to be
constructed or installed by Landlord pursuant to the provisions of the Work
Letter Agreement attached as Exhibit "C" hereto. On or before September 1, 2003,
Landlord shall construct and install in the Second Portion of the Premises the
items to be constructed or installed by Landlord pursuant to the provisions of
the Work Letter Agreement. If for any reason Landlord cannot deliver the First
Portion of the Premises to Tenant by the Commencement Date, this lease shall not
be void or voidable, and Landlord shall not be liable for any loss or damage
resulting therefrom, except that the rent payable under Paragraph 1(f) hereof
shall be waived for the period between the Commencement Date and the date on
which Landlord can deliver possession. If for any reason Landlord cannot deliver
the Second Portion of the Premises to Tenant by September 1, 2003, this Lease
shall not be void or voidable, and Landlord shall not be liable for any loss or
damage resulting therefrom, except that the rent payable under Paragraph 1(f)
hereof applicable to the Second Portion shall be waived for the period between
September 1, 2003, and the date on which Landlord can deliver possession of the
Second Portion. No delay in the delivery of possession shall extend the lease
term. Tenant may not enter or occupy the pertinent portion of the Premises until
such Portion of the Premises is tendered by Landlord, unless Tenant's entry

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relates to construction work therein. If for any reason the First Portion of the
Premises is not ready for occupancy on or before May 1, 2002, Tenant may, at its
option, cancel and terminate this lease by written notice to Landlord delivered
on or before May 15, 2002, in which event neither party shall have any further
rights or obligations hereunder, except that Landlord will pay back to Tenant
the "Prepaid Rent" (hereinafter defined). Any entry of the Premises before the
date specified in this Paragraph 2 may be made only with Landlord's written
consent. The Premises shall be deemed completed and possession delivered upon
(i) completion of the items to be constructed and installed by Landlord pursuant
to the provisions of the Work Letter Agreement attached as Exhibit "C", and (ii)
the insurance of a certificate of occupancy by the City of Richardson
(collectively "Substantial Completion") other than completion of minor finish
items, if any, which do not materially interfere with Tenant's occupancy. Upon
taking of possession of the Premises, Tenant shall be deemed to have accepted
such as suitable for its purposes and shall be deemed to have waived any defects
in the Premises and in the Building, except for the completion of any minor
finish items which do not materially interfere with Tenant's occupancy (the
"punch list items"). Tenant shall have a period of thirty (30) days from the
date of actual occupancy of the Premises to compile and deliver to Landlord the
punch list items which Landlord agrees to use its reasonable efforts to complete
or correct within ninety (90) days of receipt of said list from Tenant.

      3. Rent. In consideration of this lease, Tenant promises and agrees to pay
Landlord the basic rental (as defined in Paragraph 1(e) hereof) in monthly
installments, as set forth in Paragraph 1(f) hereof, and the additional rent as
determined in accordance with Exhibit "B", without deduction, set off, notice or
demand.

      One monthly installment of basic rental, to be applied to the first
monthly basic rental installment accruing hereunder, totaling $147,621.50
("Prepaid Rent"), shall be payable by Tenant to Landlord contemporaneously with
the execution hereof. On the first day of the second month following the date on
which basic rental begins to accrue under this lease, Tenant shall begin paying
the scheduled monthly rental installment without demand and shall continue
paying such monthly rental installments on or before the first day of each
succeeding calendar month during the term hereof. The monthly rental installment
for any fractional month at the beginning or the end of the lease term shall be
prorated.

      If the monthly rental installment is not received by the Landlord on or
before the 5th day of the month for which such monthly rental installment is
due, a service charge of 4% of the monthly rental installment owed shall become
due and payable in addition to the monthly rental installment owed. Such service
charge is for the purpose of reimbursing Landlord for the extra costs and
expenses incurred in connection with the handling and processing of late monthly
rental installment payments.

      The obligation of Tenant to pay rent is an independent covenant, and no
act or circumstance whatsoever, whether such act or circumstance constitutes a
breach of covenant by Landlord or not, shall release Tenant of the obligation to
pay rent.

      4. Rental Escalation. See Exhibit "B" attached hereto and incorporated as
a part hereof.

      5. Services.

            (a) Landlord agrees to furnish Tenant while occupying the Premises,
      at Landlord's sole cost and expense: (i) hot and cold water at those
      points of supply provided for general use of tenantry; (ii) electrical
      current for Tenant's use and occupancy of the Premises to the extent
      reasonably deemed to be standard in comparable suburban "Class A" low rise
      office buildings in Richardson, Texas, provided however, that all costs
      for extraordinary or unusual demand for electrical service shall be borne
      by Tenant; (iii) heating and air conditioning at such times as Landlord
      normally furnishes such services to all tenants of the Project and at such
      temperatures and in such amounts as are reasonably provided in comparable
      suburban "Class A" low rise office buildings in Richardson, Texas; (iv)
      janitor service on a daily basis excluding holidays and weekends and
      elevator service; (v) replacement of Building standard light bulbs and
      tubes.

            (b) Landlord does not warrant that any of such specified services
      will be free from interruption or stoppage, but nevertheless Landlord
      shall use reasonable diligence to resume any such interrupted or stopped
      service. Anything to the contrary notwithstanding, no failure, to any
      extent, to furnish such services or any stoppage or interruption of these
      defined services shall render Landlord liable in any respect for damages
      to either person, property or business, nor shall any such failure,
      interruption or stoppage of such services be deemed or construed as an
      eviction, actual or constructive, of Tenant nor, except as set forth
      below, work an abatement of rent nor relieve Tenant from the obligation to
      fulfill any covenant or agreement contained in this lease. If (a) the
      interruption or stoppage of the services to be provided by Landlord under
      Subparagraph 5(a) above is due to the negligent or willful failure of
      Landlord to use reasonable diligence during normal hours to resume any
      such interrupted or stopped service, (b) the interruption was not caused
      in whole or substantial part by Tenant, and (c) the interruption or
      stoppage caused the Premises to be uninhabitable for at least seventy-two
      (72) hours after written notice thereof from Tenant to Landlord, then
      during the period the Premises is uninhabitable, the rental shall be
      abated as Tenant's sole remedy. Landlord may interrupt or stop such
      services when reasonably needed for emergencies, repairs and maintenance
      and shall not thereby be deemed negligent or willful or in violation of
      this lease, so long as Landlord uses reasonable diligence to resume such
      interrupted or stopped services thereafter.

      6. Leasehold Improvements. See Exhibit "C".

      7. Use. Tenant shall use the Premises only for the permitted use (as
defined in Paragraph 1(h) hereof). Tenant will not occupy or use the Premises,
or permit any portion of the Premises to be occupied or used for any business or
purpose other than the permitted use or for any use or purpose which is unlawful
in part or in whole or deemed to be disreputable in any manner or extrahazardous
on account of fire, nor permit anything to be done which will in any way
increase the rate of fire insurance on the Building or contents; and in the
event that, by reason of acts of Tenant, there shall be any increase in the rate
of insurance on the Building or contents created by Tenant's acts or conduct of
business and then such acts of Tenant shall be deemed to be an event of default
hereunder and Tenant hereby agrees to pay to Landlord the amount of such
increase on demand and acceptance of such payment shall not constitute a waiver
of any of Landlord's other rights provided herein. Tenant will conduct its
business and control its agents, employees and invitees in such a manner as not
to create any nuisance, nor interfere with, annoy or disturb other tenants or
Landlord in management of the Building. Tenant will maintain the Premises in a
clean, healthful and safe condition and will comply with all laws, ordinances,
orders, rules and regulations (state, federal, municipal and other agencies or
bodies having any jurisdiction thereof) with reference to use, condition or
occupancy of Premises. Tenant's obligation to comply with all laws specifically
includes any and all laws relating to environmental hazards and, as set forth in
Subparagraph 8(c) hereof, to accessibility by persons with disabilities. Tenant
will not, without the prior written consent of Landlord, such consent not to be
unreasonably withheld, paint, install lighting, window coverings or decoration,
or install any signs, window or door lettering or advertising media of any type
on or about the Premises or any part thereof. Should Landlord agree in writing
to any of the foregoing items in the preceding sentence, Tenant will maintain
such permitted items in good condition and repair at all times.

      8. Repairs and Maintenance and Compliance with Accessibility Laws

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            (a) By Landlord: Landlord shall maintain only the roof, foundation,
      heating and air conditioning systems, common areas, plumbing, elevators
      (if any), fire protection sprinkler system (if any), the structural
      soundness of the exterior walls, the paving outside the Building, and the
      landscaping in good repair and condition, except for reasonable wear and
      tear. Landlord shall be responsible for pest eradication. If such pests
      result from Tenant's use and occupancy of the Premises, Tenant shall pay
      to Landlord on demand the cost for such eradication. Tenant shall give
      immediate written notice to Landlord of the need for repairs or
      corrections and Landlord shall proceed promptly to make such repairs or
      corrections. Landlord's liability hereunder shall be limited to the cost
      of such repairs or corrections.

            (b) By Tenant: Tenant shall at its expense and risk maintain the
      Premises and related facilities in good repair and condition. Tenant will
      not in any manner deface or injure the Building, the Premises or related
      facilities and will pay the cost of repairing any damage or injury done by
      Tenant or Tenant's agents, employees or invitees. Tenant shall throughout
      the term of this lease take good care of the Building, the Premises and
      related facilities and keep them free from waste and nuisance of any
      kind. If Tenant shall fail to make any repair required hereunder
      (including all necessary replacements) within fifteen (15) days after
      written notification to do so, or thirty (30) days if Tenant has commenced
      the repair and is diligently pursuing its completion, Landlord may at its
      option make such repair, and Tenant shall, upon demand therefor, pay
      Landlord for the cost thereof together with interest on any such cost
      which remains unpaid following such demand at the rate of ten percent
      (10%) per annum until paid.

            (c) By Landlord and Tenant: Tenant shall at its expense and risk
      cause the Premises and related facilities to be in compliance with the
      requirements of the Americans With Disabilities Act and all other
      pertinent laws relating to public access ("Accessibility Laws"). Landlord
      shall at its expense and risk cause the common areas of the Building to
      comply with Accessibility Laws. Any extraordinary or atypical requirements
      imposed by Accessibility Laws relating to the nature of Tenant's business
      shall be Tenant's responsibility and Tenant shall bear the risk and
      expense of compliance with such extraordinary or atypical requirements.
      Tenant acknowledges that Landlord's responsibility is to insure that
      common areas of the Building comply with Accessibility Laws assuming the
      imposition of requirements typical for a suburban office building.

      9. Alterations and Improvements. Tenant will not make or allow to be made
any alterations or physical additions in or to the Premises without the prior
written consent of Landlord, which consent shall not be unreasonably withheld as
to nonstructural alterations. Landlord may require, as a condition to granting
its consent to any such alterations or physical additions, that Tenant agree to
remove such alterations or physical additions at the end of the lease term and
restore the Premises to the condition in which the same existed before such
alterations or physical additions were made. At the end or other termination of
this lease, Tenant shall deliver up the Premises with all improvements located
thereon (except as otherwise herein provided) in good repair and condition,
reasonable wear and tear excepted, and shall deliver to Landlord all keys to the
Premises. The cost and expense of any repairs necessary to restore the condition
of the Premises to such condition in which they are to be delivered to Landlord
shall be borne by Tenant. All permanent alterations, additions or improvements
made in or upon the Premises, either by Landlord or Tenant, shall be Landlord's
property on termination of this lease and shall remain on the Premises without
compensation to Tenant. All temporary alterations, furniture, movable trade
fixtures and equipment installed by Tenant may be removed by Tenant at the
termination of this lease if Tenant so elects, and shall be so removed if
required by Landlord, or if not so removed shall at the option of Landlord,
become the property of Landlord. All such installations, removals and
restoration shall be accomplished in good workmanlike manner so as not to damage
the Premises or the primary structure or structural qualities of the Building or
the plumbing, electrical lines or other utilities.

      10. Common Areas. The use and occupation by Tenant of the Premises shall
include the use in common with others entitled thereto of the common areas,
parking areas, service roads, loading facilities, sidewalks, and other
facilities as may be designated from time to time by Landlord, subject, however,
to the terms and conditions of this agreement and to reasonable rules and
regulations for the use thereof as prescribed from time to time by Landlord.

      All common areas described above shall at all times be subject to the
exclusive control and management of Landlord, and Landlord shall have the right
from time to time to establish, modify and enforce reasonable rules and
regulations with respect to all facilities and areas mentioned in this Article.
Landlord shall have the right to construct, maintain, and operate lighting
facilities on all such areas and improvements; to police same; from time to time
to change the area, level, location and arrangement of parking areas and other
facilities hereinabove referred to; and subject to Exhibit "F" hereof, to
restrict parking by tenants, their officers, agents, and employees to employee
parking areas.

      All common areas and facilities not within the Premises, which Tenant may
be permitted to use and occupy, are to be used and occupied under a revocable
license, and if the amount of such areas be diminished, Landlord shall not be
subject to liability nor shall Tenant be entitled to any compensation or
diminution or abatement of rent, nor shall such diminution of such areas be
deemed constructive or actual eviction.

      11. Assignment and Subletting. If Tenant desires to assign this lease or
sublet the Premises or any part thereof, Tenant shall give Landlord written
notice of such desire together with the name of the proposed assignee or
sublessee, a detailed description of its business, and current financial
information about it in sufficient detail to allow Landlord to assess the
financial condition of such proposed assignee or sublessee. Landlord shall not
unreasonably withhold its consent to any assignment or subletting. Landlord will
consider the financial condition of the proposed assignee and/or sublessee and
will compare such financial condition to Tenant's financial condition as of
December 31, 2000, as reflected in Tenant's audited financial statement(s).
Tenant shall give such notice and information to Landlord at least 30 days prior
to the date on which Tenant desires to make such assignment or sublease. For the
purposes hereof, transfer of more than half of the stock or other voting control
of Tenant shall be deemed to constitute an assignment of this Lease. Landlord
shall, within 10 days following receipt of such notice, notify Tenant in writing
that Landlord elects either (i) to permit Tenant to assign this lease or sublet
such space, or (ii) refuse to permit Tenant to assign this lease or sublet such
space. If Landlord should fail to notify Tenant in writing of such election
within such thirty-day period, Landlord shall be deemed to have elected (ii)
above. Consent by Landlord to one or more assignments or sublettings shall not
operate as a waiver of Landlord's rights as to any subsequent assignments and
sublettings. Tenant shall pay all costs incurred by Landlord in connection with
the foregoing provisions including without limitation legal fees, construction
costs to reconfigure the Premises, and credit checks. Notwithstanding any
assignment or subletting, Tenant and any guarantor of Tenant's obligations under
this lease shall at all times remain fully responsible and liable for the
payment of the rent herein specified and for compliance with all of Tenant's
other obligations under this lease. Moreover, if the rental or other
consideration (or a combination of the rental and any bonus or other
consideration therefor or incident thereto) due and payable to Tenant by an
assignee or sublessee exceeds the rental payable under this lease (appropriately
prorated in the case of a sublease of less than all of the Premises), then
Tenant shall be bound and obligated to pay Landlord (after deduction of the
standard brokerage commission paid to the broker representing the pertinent
sublessee, if in fact such a commission is paid, and any alteration costs) fifty
percent (50%) of all such excess rental and other excess consideration within
ten (10) days after receipt thereof by Tenant. Finally,

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upon any assignment or subletting all rentals paid to Tenant by an assignee or
sublessee shall be received by Tenant in trust for Landlord, to be forwarded
immediately to Landlord. If Landlord transfers and assigns its interest in this
lease and the Building containing the Premises, Landlord shall thereby be
released from any further obligations hereunder, and Tenant agrees to look
solely to such successor in interest of the Landlord for performance of such
obligations. Tenant shall not mortgage, pledge or otherwise encumber its
interest in this lease or in the Premises. Notwithstanding anything contained
herein to the contrary, Tenant agrees not to sublease any of its Premises or
assign its lease to any lawyers or law firms in the event Haynes and Boone is a
tenant in the Building.

      12. Indemnity. Landlord shall not be liable for and Tenant will indemnify
and save harmless Landlord of and from all fines, suits, claims, demands, losses
and actions (including attorney's fees) for any injury to person or damage to or
loss of property on or about the Premises caused by the negligence or misconduct
or breach of this lease by Tenant, its agents, employees, sublessees, invitees
or by any other person entering the Building, the Premises, or related
facilities under express or implied invitation of Tenant, or arising out of
Tenant's use of the Building, the Premises, or related facilities. Landlord
shall not be liable or responsible for any loss or damage to any property or
death or injury to any person occasioned by theft, fire, Act of God, public
enemy, injunction, riot, strike, insurrection, war, court order, requisition of
any governmental body or authority, by other tenants of the Building or related
facilities or any other matter beyond control of Landlord, or for any injury or
damage or inconvenience which may arise through repair or alteration of any part
of the building, the Premises or related facilities, or failure to make repairs
or from any cause whatsoever except Landlord's gross negligence. Tenant shall,
at all times during the term of this lease, maintain a policy or policies of
insurance with the premiums thereon fully paid in advance, in amounts and with
insurance companies approved by Landlord insuring Tenant's obligations to
Landlord under Paragraph 12 of this lease. Tenant shall not be liable for and
Landlord will indemnify and save harmless Tenant of and from all fines, suits,
claims, demands, losses and actions (including attorney's fees) for any injury
to person or damage to or loss of property on or about the common areas of the
Building caused by the gross negligence or willful misconduct or breach of this
lease by Landlord, its agents or employees.

      13. Mortgages. Tenant accepts this lease subject to any deeds of trust,
security interests or mortgages which might now or hereafter constitute a lien
upon the Building or improvements therein, the Premises, or related facilities,
and to zoning ordinances and other building and fire ordinances and governmental
regulations relating to the use of the property. Tenant shall at any time
hereafter, on demand, execute any instruments, releases or other documents that
may be required by any mortgagee for the purpose of subjecting and subordinating
this lease to the lien of any such deed of trust, security interest or mortgage.
With respect to any deed of trust, security interest or mortgage hereafter
constituting a lien on the Building or improvements therein, the Premises, or
related facilities. Landlord, at its sole options, shall have the right to waive
the applicability of this Paragraph 13 so that this lease will not be subject
and subordinate to any such deed of trust, security interest or mortgage.

      14. Insurance. Landlord shall, at all times during the term of this lease
maintain a policy or policies of insurance with the premiums thereon fully paid
in advance, issued by and binding upon some solvent insurance company, insuring
the Building against loss or damage by fire, explosion, or other hazards and
contingencies for the full insurable value thereof; provided that Landlord shall
not be obligated to insure any furniture, equipment, machinery, goods or
supplies not covered by this lease which Tenant may bring or obtain upon the
Premises, or any additional improvements which Tenant may construct thereon.

      Tenant shall, at all times during the term of this lease, maintain a
policy or policies of insurance, with the premiums thereon fully paid in
advance, issued by and binding upon insurance companies approved by Landlord,
such approval not to be unreasonably withheld, insuring any furniture,
equipment, machinery, goods or supplies which Tenant may bring or obtain upon
the Premises, and any additional improvements which Tenant may construct on the
Premises against loss or damage by fire, explosion or other hazards and
contingencies for the full insurable value thereof. Tenant shall also, at all
times during the term of this lease, maintain a policy or policies of insurance,
with the premiums thereon fully paid in advance, for comprehensive general and
contractual liability insurance against claims for personal injury, death and
property damage occurring in or about the Premises, such insurance to afford
protection to the limits of (i) not less than $1,000,000.00 in respect of injury
to or death of any number of persons arising out of any one occurrence, and not
less than $2,000,000.00 in the aggregate, and (ii) $1,000,000.00 in respect of
any instance of property damage. Such policy or policies shall be issued by and
binding upon insurance companies approved by Landlord, such approval not to be
unreasonably withheld.

      Tenant shall deliver to Landlord, prior to the Commencement Date,
certificates of such insurance and shall, at all times during the term of this
lease, deliver to Landlord upon request true and correct copies of such
insurance policies. The comprehensive general and contractual liability policy
described above shall (i) name Landlord as an additional insured, (ii) insure
performance of the indemnities of Tenant contained in this lease, and (iii) be
primary coverage, so that any insurance coverage obtained by Landlord shall be
in excess thereof. Each insurance policy obtained by Tenant shall provide that
it will not be canceled or reduced in coverage without 30 days prior written
notice to Landlord. Tenant shall deliver to Landlord certificates of renewal at
least 5 days prior to the expiration date of each such policy and copies of new
policies at least 30 days prior to terminating any such policies.

      15. Inspection. Except as set forth below but always in the case of an
emergency, Landlord or representatives shall have the right to enter into and
upon any and all parts of the Premises at reasonable hours to (i) inspect same
or clean or make repairs or alterations or additions as Landlord may reasonably
deem necessary (but without any obligation to do so, except as expressly
provided for herein), or (ii) show the Premises to prospective tenants,
purchasers or lenders, and Tenant shall not be entitled to any abatement or
reduction of rent by reason thereof, nor shall such be deemed to be an actual or
constructive eviction. Notwithstanding the above, except in the case of an
emergency, Landlord acknowledges and agrees that Tenant intends to maintain
certain "secured" areas within the Premises relating to its business and trade
secrets and Landlord shall only be permitted within such areas after giving no
less than 24 hours prior written notice to Tenant and Landlord must be
accompanied in any such areas by a representative of Tenant.

      16. Condemnation. If, during the term of this lease, or any extension or
renewal thereof, all of the Premises should be taken for any public or
quasi-public use under any governmental law, ordinance or regulation or by right
of eminent domain or by private purchase in lieu thereof, this lease shall
terminate and the rent shall be abated during the unexpired portion of this
lease, effective on the date physical possession is taken by the condemning
authority, and Tenant shall have no claim against Landlord for the value of any
unexpired term of this lease.

      In the event a portion but not all of the Premises shall be taken for any
public or quasi-public use under any governmental law, ordinance or regulation,
or by right of eminent domain or by private sale in lieu thereof and the partial
taking or condemnation shall render the Premises unsuitable for Tenant's
business, then Landlord shall have the option, in its sole discretion, of
terminating this lease, or, at Landlord's sole risk and expense, restoring and
reconstructing the Premises to the extent necessary to make same reasonably
tenantable. Should Landlord elect to restore, the lease shall continue in full
force and effect with the rent payable during the unexpired portion of this
lease adjusted to such an extent as may be fair and reasonable under the
circumstances, and Tenant shall have no claim against Landlord for the value of
any interrupted portion of this lease.

      In the event of any condemnation or taking, total or partial, Tenant shall
not be entitled to any part of the award or price paid in lieu thereof, and
Landlord shall receive the full amount of such award or price, Tenant hereby
expressly waiving any right or claim to any part thereof.

      17. Fire or Other Casualty. In the event that the Premises should be
totally destroyed by fire, tornado or other casualty or in the event the
Premises or the Building should be so damaged that rebuilding or repairs cannot
be completed within 180 days after the date of such damage, either Landlord or
Tenant may at its option terminate this lease by delivering written notice
thereof to the

                                       4
<PAGE>

other party within twenty (20) days following such damage, in which event the
rent shall be abated during the unexpired portion of this lease effective with
the date of such damage. In the event the Premises should be damaged by fire,
tornado or other casualty covered by Landlord's insurance, but only to such
extent that rebuilding or repairs can be completed within 180 days after the
date of such damage, or if the damage should be more serious but neither
Landlord nor Tenant elects to terminate this lease, in either such event
Landlord shall within thirty (30) days after the date of such damage commence to
rebuild or repair the Premises and shall proceed with reasonable diligence to
restore the Premises and Building to substantially the same condition in which
they were immediately prior to the happening of the casualty, except that
Landlord shall not be required to rebuild, repair or replace any part of the
furniture, equipment, fixtures and other improvements, except Tenant
improvements made by Landlord, which may have been placed by Tenant or other
tenants within the Building or the Premises, or related facilities. In the event
that the Premises are totally untenantable, Landlord shall abate the rent during
the time Premises are unfit for occupancy. If the Premises are not totally
untenantable, Landlord shall allow Tenant a fair diminution of rent during the
time the Premises are partially unfit for occupancy. In the event any mortgagee
under a deed of trust, security agreement or mortgage elects pursuant to a right
granted therein that insurance proceeds be used to retire the mortgage debt,
Landlord shall have no obligation to rebuild and this lease shall terminate upon
notice to Tenant which shall be given promptly to Tenant after Landlord has been
notified by mortgage. Any insurance which may be carried by Landlord or Tenant
against loss or damage to the Project or to the Premises shall be for the sole
benefit of the party carrying such insurance and under its sole control.

      18. Holding Over. Should Tenant, or any of its successors in interest,
hold over the Premises, or any part thereof, after the expiration of the term of
this lease, unless otherwise agreed in writing, such holding over shall
constitute and be construed as tenancy at sufferance only. Such tenancy shall be
at a daily rental equal to 1/30th of the higher of (i) 150% of the sum of the
monthly rental installment plus the most current rental adjustment which may
have been made thereto pursuant to Paragraph 4 hereof, or (ii) 150% of the
current rate for the Premises being quoted by Landlord to prospective tenants.
The inclusion of the preceding sentence shall not be construed as Landlord's
consent for the Tenant to hold over. In the event of any unauthorized holding
over, Tenant shall also indemnify Landlord against all claims for damages by any
other tenant to whom Landlord may have leased all or any part of the Leased
Premises effective upon the termination of this lease. Notwithstanding the
foregoing during the first month of any holdover, and only during that first
month, the daily rental rate shall be equal to 1/30th of 110% of the sum of the
monthly rental installment plus the most current rental adjustment which may
have been made thereto pursuant to Paragraph 4 hereof.

      19. Taxes on Tenant's Property. Tenant shall be liable for all taxes
levied or assessed against personal property, furniture or fixtures placed by
Tenant in the Premises. If any such taxes for which Tenant is liable are levied
or assessed against Landlord or Landlord's property and if Landlord elects to
pay the same or if the assessed value of Landlord's property is increased by
inclusion of personal property, furniture or fixtures placed by Tenant in the
Premises, and Landlord elects to pay the taxes based on such increase, Tenant
shall pay to Landlord upon demand that part of such taxes for which Tenant is
primarily liable hereunder.

      20. Events of Default. The following events shall be deemed to be events
of default by Tenant under this lease:

            (a) Tenant shall fail to pay any monthly rental installment or any
      portion of the basic rental hereby reserved when due, and shall not cure
      such failure within ten (10) days after written notice thereof to Tenant;

            (b) Tenant shall fail to comply with any term, provision or covenant
      of this lease, other than the payment of rent, or shall fail to comply
      with any term, provision or covenant in any other agreement with Landlord
      affecting the Premises, and shall not cure such failure within thirty
      (30) days after written notice thereof to Tenant;

            (c) Tenant shall make an assignment for the benefit of creditors;

            (d) Tenant shall file a petition under any section or chapter of the
      Federal Bankruptcy Code, as amended, or under any similar law or statute
      of the United States or any State thereof, or Tenant shall be adjudged
      bankrupt or insolvent in any proceeding filed against Tenant thereunder
      and such adjudication shall not be vacated or set aside within thirty (30)
      days;

            (e) A receiver or Trustee shall be appointed for all or
      substantially all of the assets of Tenant and such receivership shall not
      be terminated or stayed within thirty (30) days; or

            (f) Tenant shall assign this lease or sublet the Premises without
      Landlord's consent, where Landlord's consent is required under Section 11.

      21. Remedies. Upon the occurrence of any event of default specified in
Paragraph 20 hereof, Landlord shall have the option to pursue any one or more of
the following remedies without any notice or demand whatsoever:

            (a) Terminate this lease in which event Tenant shall immediately
      surrender the Premises to Landlord, and if Tenant fails to do so, Landlord
      may, without prejudice to any other remedy which it may have for
      possession or arrearages in rent, enter upon and take possession and expel
      or remove Tenant and any other person who may be occupying such Premises
      or any part thereof, without being liable for prosecution or any claim of
      damages therefor. Tenant agrees to pay to Landlord on demand the amount of
      all loss and damage which Landlord may suffer by reason of such
      termination, including (i) the cost of recovering the Premises (including
      attorneys' fees and costs of suit), (ii) the cost of removing and storing
      any personal property, (iii) the unpaid rent earned at the time of
      termination, plus interest thereon at the rate described in Paragraph 35,
      (iv) the present value (discounted at the rate of six percent (6%) per
      annum) of the balance of the basic rental and additional rental for the
      remainder of the lease term less the present value (discounted at the same
      rate) of the fair market rental value of the Premises for such period,
      taking into account the period of time the Premises will remain vacant
      until a new tenant is obtained, and the cost to prepare the Premises for
      occupancy and the other costs (such as costs of repairs or remodeling,
      leasing commissions and attorneys' fees) to be incurred by Landlord in
      connection therewith, and (v) any other sum of money and damages owed by
      Tenant to Landlord under this lease;

            (b) Enter upon and take possession of the Premises and expel or
      remove Tenant and any other person who may be occupying the Premises or
      any part thereof, without being liable for prosecution or any claim for
      damages therefor, and if Landlord so elects, relet the Premises on such
      terms as Landlord shall deem advisable and receive the rent thereof.
      Tenant agrees to pay to Landlord on demand any deficiency in basic rental
      that may arise by reason of such reletting;

            (c) Enter upon the Premises, without being liable for prosecution or
      any claim for damages therefor, and do whatever Tenant is obligated to do
      under the terms of this lease, and tenant agrees to reimburse Landlord on
      demand for any expenses which Landlord may incur in thus effecting
      compliance with Tenant's obligations under this lease, and Tenant further
      agrees that Landlord shall not be liable for any damages resulting to the
      Tenant from such action; and

            (d) Landlord may, and is hereby entitled and authorized, without any
      notice to Tenant whatsoever, to enter upon the premises by use of a master
      key, a duplicate key, or other peaceable means, and to change, alter,
      and/or modify the door locks on all entry doors of the premises, thereby
      permanently excluding Tenant and its officers, principals, agents,
      employees, and representatives therefrom. If Landlord has either
      permanently repossessed the Premises pursuant to the foregoing provisions
      of this Lease, or has terminated this lease by reason of Tenant's default,
      Landlord shall not thereafter be obligated to provide Tenant with a key to
      the Premises at any time; provided, however, that in any such instance,
      during

                                       5
<PAGE>

      Landlord's regular business hours and at the convenience of Landlord, and
      upon the written request of Tenant accompanied by such written waivers and
      releases as Landlord may require, Landlord will escort Tenant or its
      authorized personnel to the Premises to retrieve any personal belongings
      or other property of Tenant not subject to the lien or security interest
      described herein. If Landlord elects to exclude Tenant from the Premises
      without permanently repossessing or terminating pursuant to the foregoing
      provisions of this lease, then Landlord (at any time prior to actual
      repossession or termination) shall not be obligated to provide Tenant a
      key to re-enter the Premises until such time as all delinquent rental and
      other amounts due under this lease have been paid in full (and all other
      defaults, if any, have been completely cured to Landlord's satisfaction)
      and Landlord has been given assurance reasonably satisfactory to Landlord
      evidencing Tenant's ability to satisfy its remaining obligations under
      this lease. During any such temporary period of exclusion, Landlord will,
      during Landlord's regular business hours and at Landlord's convenience,
      upon written request by Tenant, escort Tenant or its authorized personnel
      to the Premises to retrieve personal belongings of Tenant or its
      employees. This remedy of Landlord shall override and control any
      conflicting provisions of the Texas Property Code.

      No re-entry or taking possession of the Premises by Landlord shall be
construed as an election on its part to terminate this lease, unless a written
notice of such intention be given to Tenant. Notwithstanding any such reletting
or re-entry or taking possession, Landlord may at any time thereafter elect to
terminate this lease for a previous default. Pursuit of any of the foregoing
remedies shall not preclude pursuit of any of the other remedies herein provided
or any other remedies provided by law, nor shall pursuit of any remedy herein
provided constitute a forfeiture or waiver of any rent due to Landlord hereunder
or of any damages accruing to Landlord by reason of the violation of any of the
terms, provisions and covenants herein contained. Landlord's acceptance of rent
following an event of default hereunder shall not be construed as Landlord's
waiver of such event of default. No waiver by Landlord of any violation or
breach of any of the terms, provisions, and covenants herein contained shall be
deemed or construed to constitute a waiver of any other violation or breach of
any of the terms, provisions, and covenants herein contained. Forbearance by
Landlord to enforce one or more of the remedies herein provided upon an event of
default shall not be deemed or construed to constitute a wavier of any other
violation or default.

      22. Surrender of Premises. No act or thing done by the Landlord or its
agents during the term hereby granted shall be deemed as acceptance of a
surrender of the Premises, and no agreement to accept a surrender of the
Premises shall be valid unless the same be made in writing and subscribed by the
Landlord.

      23. Attorneys' Fees. In case it should be necessary or proper for Landlord
or Tenant to bring any action under this lease or to consult or place such
lease, or any amount payable by Landlord or Tenant thereunder, with an attorney
concerning or for the enforcement of any of Landlord's or Tenant's rights
hereunder, then the non-prevailing party agrees in each and any such case to
pay the prevailing party on demand a reasonable attorney's fee.

      24. Intentionally deleted.

      25. Mechanic's Lien. Tenant will not permit any mechanic's lien or liens
to be placed upon the Premises or the Project or improvements thereon during the
term hereof caused by or resulting from any work performed, materials furnished
or obligation incurred by or at the request of Tenant, and in the case of the
filing of any such lien Tenant will promptly pay same. If default in payment
thereof shall continue for twenty (20) days after written notice thereof from
Landlord to the Tenant, the Landlord shall have the right and privilege at
Landlord's option of paying the same or any portion thereof without inquiry as
to the validity thereof, and any amounts so paid, including expenses and
interest, shall be so much additional rent hereunder due from Tenant to Landlord
and shall be repaid to Landlord immediately on rendition of bill therefor,
together with interest until repaid as provided in Paragraph 35. Tenant will
have the option to "bond around" any mechanic's lien, or liens, provided such
bonding around is in accordance with and permitted by deeds of trust or
mortgages affecting the Building.

      26. Waiver of Subrogation. Anything in this lease to the contrary
notwithstanding, the parties hereto hereby waive any and all rights of recovery,
claim action or cause of action, against each other, their agents, officers, and
employees, for any loss or damage that may occur to the Premises hereby demised,
or any improvements thereof, or such Project of which the Premises are a part,
any improvements thereto, or related facilities, by reason of fire, the
elements, or any other cause which could be insured against under the terms of
standard fire and extended coverage insurance policies, regardless of cause or
origin, including negligence of the parties hereto, their agents, officers and
employees.

      No insurer of one party hereunder shall hold any right of subrogation
against the other party. If the respective insurer of Landlord and Tenant does
not permit the foregoing waiver without an appropriate endorsement to such
party's insurance policy, then Landlord and Tenant each covenant and agree to
notify its insurer of the waiver set forth herein and to secure from such
insurer an appropriate endorsement to its respective insurance policy with
respect to such waiver.

      27. Notices. Each provision of the Agreement, or of any applicable
governmental laws, ordinances, regulations, and other requirements with
reference to the sending, mailing or delivery of any notice, or with reference
to the making of any payment by Tenant to Landlord, shall be deemed to be
complied with when and if the following steps are taken:

      (a) All rent and other payment required to be made by Tenant to Landlord
      hereunder shall be payable to Landlord in Dallas County, Texas, at the
      address hereinbelow set forth, or at such other address as Landlord may
      specify from time to time by written notice delivered in accordance
      herewith;

      (b) Any notice or document required to be delivered hereunder shall be
      deemed to be delivered if actually received and whether or not received
      when deposited in the United States mail, postage prepaid, certified or
      registered mail (with or without return receipt requested) addressed to
      the parties hereto at the respective addresses set out opposite their
      names below, or at such other address as they have heretofore specified by
      written notice delivered in accordance herewith;

      LANDLORD:  TR Lookout Partners. Ltd.
                 c/o Thompson Realty Corporation
                 1600 N. Collins, Suite 2100
                 Richardson, Texas 75080

      TENANT:    telecom technologies, inc.
                 1701 N. Collins, Suite 3000 (prior to the Commencement Date)
                 1301 E. Lookout Drive, Suite 3000 (after the Commencement Date)
                 Richardson, Texas 75080 (in both instances)
                 Attn: Hamid Ansari (with an additional separate copy to
                       Anousheh Ansari)

                 With a copy to:
                 Robert L. Abbott
                 Stutzman & Bromberg. P.C.
                 2323 Bryan St., Suite 2200
                 Dallas, Texas 75201

      28. Force Majeure. Whenever a period of time is herein prescribed for
action to be taken by either party, specifically excluding Tenant's obligation
to pay rent and other monetary obligations of Tenant hereunder, such party shall
not be liable or responsible for, and there shall be excluded from the
computation of any such period of time, any delays due to strikes, riots, Acts
of God, shortages of labor or materials, war, governmental laws, regulations or
restrictions or any other causes of any kind whatsoever which are beyond the
control of such party.

                                       6
<PAGE>

      29. Separability. If any clause or provision of this lease is illegal,
invalid or unenforceable under present or future laws effective during the term
of this lease, then and in that event, it is the intention of the parties hereto
that the remainder of this lease shall not be affected thereby, and it is also
the intention of the parties to this that in lieu of each clause or provision of
this lease that is illegal, invalid, or unenforceable, there be added as part of
this lease a clause or provision as similar in terms to such illegal, invalid or
unenforceable clause or provision as may be possible and be legal, valid and
enforceable.

      30. Entire Agreement; Amendments; Binding Effect. This lease contains the
entire agreement between the parties and may not be altered, changed or amended,
except by instrument in writing signed by both parties hereto. No provision of
this lease shall be deemed to have been waived by Landlord unless such waiver be
in writing signed by Landlord and addressed to Tenant, nor shall any custom or
practice which may grow up between the parties in the administration of the
terms hereof be construed to waive or lessen the right of Landlord to insist
upon the performance by Tenant in strict accordance with the terms hereof. The
terms, provisions, covenants and conditions contained in this lease shall apply
to, inure to the benefit of, and binding upon the parties hereto, and upon their
respective successors in interest and legal representatives, except as otherwise
herein expressly provided.

      31. Quiet Enjoyment. Provided Tenant has performed all of the terms,
covenants, agreements and conditions of this lease, including the payment of
rent, to be performed by Tenant, Tenant shall peaceably and quietly hold and
enjoy the Premises for the term hereof, without hindrance from Landlord, subject
to the terms and conditions of this lease.

      32. Rules and Regulations. Tenant and Tenant's agents, employees, and
invitees will comply fully with all requirements of the rules and regulations of
the Project and related facilities which are attached hereto as Exhibit "D" and
made a part hereof as though fully set out herein. Provided additional
expenditures are not required by Tenant, Landlord shall at all times have the
right to change such rules and regulations or to promulgate other rules and
regulations in such reasonable manner as may be deemed advisable for safety,
care, or cleanliness of the Project, the Premises, or related facilities, and
for preservation of good order therein all of which rules and regulations,
changes and amendments will be forwarded to Tenant in writing and shall be
carried out and observed by Tenant. Tenant shall further be responsible for the
compliance with such rules and regulations by the employees, servants, agents,
visitors and invitees of Tenant.

      33. Broker's or Agent's Commission. Tenant represents and warrants that
there are no claims for brokerage commissions or finder's fees in connection
with the execution of this lease, and Tenant agrees to indemnify and hold
harmless Landlord against all liabilities and costs arising from such claims,
including without limitation attorneys' fees in connection therewith resulting
from any other claims arising by or through Tenant.

      34. Intentionally deleted.

      35. Interest. Any rent or other amount which becomes owing by Tenant to
Landlord under this lease (including unpaid service charges) shall bear
interest from the date of demand at the lesser of the highest lawful rate or ten
percent (10%) per annum.

      36. Estoppel Certificate. Tenant will, at any time and from time to time,
upon not less than ten (10) days' prior request by Landlord, execute,
acknowledge and deliver to Landlord a statement in writing executed by Tenant
certifying that this lease is unmodified and in full effect (or, if there have
been modifications, that this lease is in full effect as modified, and setting
forth such modifications) and the dates to which the rent has been paid, and
either stating that to the knowledge of the signer of such certificate no
default exists hereunder or specifying each such default of which the signer may
have knowledge; it being intended that any such statement by Tenant may be
relied upon by any prospective purchaser or mortgagee of the Project.

      37. Landlord's Liability. The liability of Landlord to Tenant for any
default by Landlord under the terms of this lease shall be limited to the
proceeds of sale on execution of the interest of Landlord in the Building and
Landlord shall not be personally liable for any deficiency. This clause shall
not be deemed to limit or deny any remedies which Tenant may have in the event
of default by Landlord hereunder, which do not involve the personal liability of
Landlord.

      38. Captions. The captions contained in this lease are for convenience of
reference only, and in no way limit or enlarge the terms and conditions of this
lease.

      39. Gender. Words of any gender used in this lease shall be held and
construed to include any other gender, and words in the singular number shall be
held to include the plural, unless the context otherwise requires.

      40. Place of Performance. Tenant shall perform all covenants, conditions
and agreements contained herein, including but not limited to payment of rent,
in Collin County, Texas. Any suit arising from or relating to this agreement
shall be brought in Dallas County, Texas.

      41. Relocation. Intentionally deleted.

      42. Reception Area. Landlord has agreed to allow Tenant to locate a
reception desk in the lobby area of the Building in a mutually acceptable
location. The design and installation of the reception desk will be subject to
Landlord's approval, not to be unreasonably withheld. Tenant will pay annual
rental of $19.50 per square foot of rentable area occupied by the reception desk
for months 1-60 of the lease term, and $22.25 per square foot of rentable area
for months 61-84. Basic rental set forth in Paragraph 1(e) and the monthly
rental installment set forth in Paragraph l(f) will be increased to cover
reception area rental described herein as long as such reception area is
required by Tenant. Tenant must, at its sole cost and expense, restore the lobby
area at such time as Tenant chooses to eliminate the lobby reception desk.

      43. Signage. Tenant, at its sole cost and expense (subject to Paragraph 7
of the Work Letter Agreement), subject to Landlord's approval, not to be
unreasonably withheld, and subject to City of Richardson approval(s), shall have
the right to install non-exclusive signage on the top of the Building in
accordance with the drawing attached hereto as Exhibit "G". Exhibit "G" also
indicates the location of Haynes and Boone, LLP signage ("H and B Signage").
Landlord agrees that the H and B Signage will not be moved from the north side
of the Building without Tenant's consent. Landlord also agrees that if Haynes
and Boone vacates the Building, for so long as Tenant occupies the Premises and
no default exists and is continuing under this lease, Tenant will have the
exclusive right to exterior Building signage. If Landlord ever constructs a
Building monument sign, and so long as no uncured event of default exists under
this lease Tenant, Tenant will be entitled, at its sole cost and expense, to
install signage on the panel of Tenant's choice on such monument sign. Tenant
may utilize the "Credit" (hereinafter defined) with respect to signage costs.

      44. Emergency Generator. Landlord will, on an as-needed basis, provide
Tenant rent free, with a mutually agreeable and unobtrusive location exterior to
the Building, to locate an emergency generator owned by Tenant. The Building
will have its own emergency generator.

      45. Existing Leases. Landlord and Tenant acknowledge that Tenant is
obligated as tenant through April 30, 2003, under those certain Office Lease
Agreements with Collins Campbell Joint Venture ("Collins"), as Landlord relating
to approximately 48,970 square feet of rentable area in the office building(s)
located at 1701 N. Collins Blvd., Richardson, Texas, and commonly referred to as
"The Atrium on Collins Phase I and Phase II". Those existing office leases
include but are not limited to an office lease (i) dated April 4, 1997, as
amended, relating to 38,016 square feet of rentable area, (ii) dated October 14,
1999, as amended, relating to 2,055 square feet, (iii) dated January 25, 2000,
relating to 2,281 square feet of rentable area, and (iv) dated January 25, 2000,
as amended, relating to 6618 square feet of rentable area, these described
leases set forth above together with any other leases executed by Tenant with
respect to space in the Atrium on Collins

                                       7
<PAGE>

Phase I and Phase II being collectively referred to as the "Existing Leases".
Landlord agrees that, if for any reason Tenant is called upon by Collins,
Principal Mutual Life Insurance Company or any other party to pay any rent or
other amounts under the Existing Leases subsequent to taking possession and
occupancy of the Premises under this Lease, and paying to Collins $150,000 in
cash, which payment shall be due and payable within ten (10) days of Tenant
taking possession and occupancy of the premises hereunder, Tenant shall be
entitled to a dollar-for-dollar right of offset of any amounts paid under the
Existing Leases against any and all amounts owing by Tenant under this Lease.

      46. Basement Area. Landlord leases to Tenant and Tenant leases from
Landlord 6,841 square feet of rentable area, as shown on Exhibit "H" attached
hereto, of basement space (the "Basement Area"). The Basement Area will be
suitable for storage, and except where wall is part of the concrete structure of
the Building, Landlord will at its expense finish-out the Basement Area with
sheet rock walls, lighting, plumbing stub-out, electrical lines to junction box,
sprinkler system, main ducting for the HVAC system, and limited air-conditioning
suitable for dead storage space. Basic rental set forth in Paragraph 1(e) and
the monthly rental installment set forth in, Paragraph 1(f) will be increased to
cover Basement Area rental at a rate of $12.00 per year per square foot of
Basement Area. In the event Tenant decides to convert a portion of the Basement
Area into a workout facility and employee lunch room, Landlord agrees to
additionally install building standard ceiling and lighting at Landlord's
expense. Tenant agrees that there will be no additional Credit, as defined in
Paragraph 7 of Exhibit "C" with respect to the Basement Area.

      47. Workout Facility. In the event Tenant elects to convert a portion of
the basement area into a workout facility, Tenant agrees to allow twenty-five
(25) Haynes and Boone, LLP ("H and B") employees at a cost of $25.00 per month
per user, and five (5) Thompson Realty Corporation ("TRC") employees the right
to use the workout facility at a cost of $75.00 per month per user. TRC agrees
to collect the monthly user fees for any H and B or TRC users and remit the same
to Tenant. Only the TRC user fees are guaranteed to be paid to Tenant and such
guaranty is only in effect if TRC occupies space in the Building.

      48. Roof Rights. Tenant will have the non-exclusive right to install
telecommunications and/or satellite equipment on the roof of the Building at
Tenant's sole cost and expense, but with no additional rental being charged by
Landlord in connection therewith. Landlord will have the right to approve all
specific equipment, such approval not to be unreasonably withheld. Use of the
roof by other tenants of the Building is contemplated.

      49. Fiber Optic Access. Landlord shall provide, at no cost to Tenant, a
minimum of twelve (12) four inch sleeves at each phone room.

      50. Non-Disturbance Agreement. Landlord will obtain a non-disturbance
agreement for Tenant's benefit from the existing mortgage lien holder on the
Building.

      51. Lease Submission. The submission of this Lease to Tenant shall not be
construed as an offer, nor shall Tenant have any rights with respect hereto
unless and until Landlord shall execute a copy of this lease and deliver the
same to Tenant.

      52. Early Occupancy of the Second Portion. Notwithstanding anything
contained herein to the contrary, in the event Tenant occupies the Second
Portion prior to September 1, 2003, Tenant will pay only for the period of early
occupancy prior to and including August 31, 2003, "Electrical Costs" and "Basic
Cost", as defined in Exhibit "B", with respect to the Second Portion. No "Basic
Costs Stop" as defined in Exhibit "B", will apply to the Second Portion during
the period of early occupancy, if any, nor will a monthly rental installment.
Effective September 1, 2003, the monthly rental installment in Section 1(f) will
apply to the First Portion and the Second Portion.

      53. Special Provisions. Exhibits "A", "B", "C", "D", "E", "F", "G", Rider
No. 101, Rider No. 201, Rider No. 301, Rider No. 301-B and Rider No. 401.

                    LANDLORD:   TR Lookout Partners, Ltd.,
                                  a Texas limited partnership

                                    By: Thompson Realty Investment Corporation,
                                          a Texas Corporation

                                      By: /s/ W.T. Field
                                          --------------------------------------
                                          W.T. Field, President

                    TENANT:     telecom technologies, inc.

                                By: /s/ Anousheh Ansari
                                    -------------------------------
                                    Anousheh Ansari
                                    President & Chief Executive Officer

                                       8<PAGE>

                                                                   Exhibit 10.21

                    FIRST AMENDMENT TO OFFICE LEASE AGREEMENT

      THIS FIRST AMENDMENT TO OFFICE LEASE AGREEMENT (this "First Amendment") is
made and entered into effective as of January 8, 2001, by and between TR Lookout
Partners, Ltd. ("Landlord") and telecom technologies, inc. ("Tenant").

                                    RECITALS

      WHEREAS, Landlord and Tenant entered into that certain Office Lease
Agreement dated as of November 14, 2000 (the "Lease"), with respect to certain
Premises defined therein and commonly known as Suite 3000, 1301 E. Lookout
Drive, Richardson, Texas, which Lease is incorporated herein by reference; and

      WHEREAS, Landlord and Tenant desire to amend the Lease to increase the
size of the premises, the rental and the tenant improvement allowance.

      NOW, THEREFORE, in consideration of the mutual agreements herein set forth
and set forth in the Lease, and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, Landlord and Tenant
have agreed, and do hereby agree, as follows:

      1.    All terms used herein and not specifically defined shall have the
            same meaning herein as is ascribed to them in the Lease.

      2.    Notwithstanding anything contained to the contrary in the first
            paragraph of "RIDER NO. 201" and in EXHIBIT "C-201" to the Lease,
            the Premises are hereby increased to 119,966 square feet of rentable
            area by adding the 10,000 square feet of rentable area on the second
            floor (the Expansion Space) to the First Portion, which increases
            the First Portion from 91,684 square feet of rentable area to
            101,684 square feet of rentable area. This revised First Portion is
            described on Exhibit "A" to this First Amendment, which is attached
            hereto and incorporated herein for all purposes.

      3.    Basic rental under the Lease, as set forth in Paragraph 1(e), is
            increased from $14,902,174.00 to $16,896,818.00. ($574,644.00 is
            attributable to the Basement Area which is 6,841 square feet of
            rentable area).

      4.    The monthly rental installment as set forth in Paragraph 1(f) of the
            Lease is increased as set forth below:

<TABLE>
<CAPTION>
Time Period                 Rentable Area           Monthly Rental       Annual Rental Rate
                         (except for Basement         Installment         Per Square Foot
                                 Area)                                      (except for
                                                                           Basement Area)

<S>                             <C>          <C>                              <C>
Monthly from
Sept. 1, 2001 through
August 31, 2003                 101,684              $172,077.50              $19.50
                                                 (not $148,986.50)
                                             ($6,841.00 is attributable
                                                  to Basement Area)

Monthly from
Sept. 1, 2003 through
August 31, 2006                 119,966              $201,785.75              $19.50
                                                 (not $178,694.75)
                                             ($6,841.00 is attributable
                                                  to Basement Area)

Monthly from
Sept. 1, 2006 through
August 31, 2008                 119,966              $229,277.96              $22.25
                                                 (not $203,876.96)
                                             ($6,841.00 is attributable
                                                  to Basement Area)
</TABLE>

      5.    Notwithstanding anything contained to the contrary in Exhibit
            "C-201" to the Lease, Landlord and Tenant agree the Expansion Space
            is now part of the First Portion of the Premises, and, as such, is
            subject to the provisions of Exhibit "C" to the Lease, the WORK
            LETTER AGREEMENT, specifically including Section 7.
<PAGE>

First Amendment to Office Lease Agreement
Page 2 of 2

      6.    The additional tenant improvement allowance contained in Section 8
            of Exhibit "C" with respect to the First Portion shall be increased
            as follows:
            September 1, 2001, First Portion From: $522,754.00 To: $586,654.00

      7.    Paragraph 1 of RIDER NO. 201 to the Lease, OPTION TO EXPAND, is
            hereby deleted in its entirety and is of no further force or
            effect.

      8.    The Right of First Refusal Space (the Growth Area) identified in
            RIDER NO. 301 to the Lease, RIGHT OF FIRST REFUSAL, is hereby
            decreased from 38,285 square feet of rentable area to 28,285 square
            feet of rentable area.

      9.    Except as herein provided to the contrary, Tenant's lease of the
            Expansion Space from Landlord pursuant hereto shall be on the same
            terms and conditions as those specified in the Lease.

      10.   The Lease (as amended by this First Amendment) remains in full force
            and effect and is hereby ratified and affirmed.

      11.   Exhibit "A" to this First Amendment replaces and supercedes Exhibit
            "A" to the Lease.

      12.   Prepaid Rent is hereby increased from $148,986.50 to $165,236.50.
            Tenant has previously paid Prepaid Rent equal to $148,986.50 to
            Landlord. Additional Prepaid Rent of $16,250.00 shall be payable by
            Tenant to Landlord contemporaneously with the execution hereof.

      13.   The submission of this First Amendment to Tenant shall not be
            construed as an offer, nor shall Tenant have any rights with respect
            hereto, unless and until Landlord shall execute a copy of this First
            Amendment and deliver the same to Tenant.

      IN WITNESS WHEREOF, this First Amendment is hereby executed effective as
of the day and year first set forth above.

                                LANDLORD:

                                TR Lookout Partners, Ltd.
                                  a Texas limited partnership

                                By: Thompson Realty Investment Corporation,
                                      a Texas Corporation

                                      By: /s/ W.T. Field
                                          --------------------------------------
                                          W.T. Field, President

                                TENANT:

                                telecom technologies, inc.

                                By: /s/ Anousheh Ansari
                                    -------------------------------
                                    Anousheh Ansari

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