<PAGE>

                                                                   EXHIBIT 10.51

                       ASSIGNMENT AND ASSUMPTION OF LEASE

     This Assignment and Assumption of Lease (the "Assignment") is made on
January 29, 2002 by and between Leap Wireless International, Inc., a Delaware
corporation, with a place of business at 10307 Pacific Center Ct., San Diego,
California 92121 ("Leap" or "Assignee"), and Electronic Arts Inc., a Delaware
corporation, with a place of business at 209 Redwood Shores Parkway, Redwood
City, California 94065 ("Electronic Arts" or "Assignor"). Leap and EA may be
referred to from time to time in this Agreement individually as a "Party" and
collectively as the "Parties."

                                    RECITALS:

This Assignment is made with regard to the following facts:

A.   Landlord, (as successor in interest to Spieker Properties, L.P.) as
landlord, and Assignor, as tenant, are parties to that certain Office Lease
dated September 3, 1999 (the "Office Lease"), as amended by that certain First
Amendment to Lease dated February 14, 2000 (the "First Amendment")
(collectively, the "Lease") pursuant to which Landlord has leased to Assignor
certain premises containing approximately 10,981 rentable square feet (the
"Premises") known as Suite No. 200 on the 2nd floor of the building commonly
known as Pacific Ridge Corporate Centre and located at 5790 Fleet Street,
Carlsbad, CA 92008 (the "Building"). A copy of the Office Lease and the First
Amendment are attached hereto as Exhibit A and are incorporated by reference;
and

     B.   Assignor desires to assign its rights, title, and interest in, to, and
under the Lease and the Premises to Assignee, and Assignee desires to accept
that assignment on, and subject to, all of the terms and conditions in this
Assignment and the Landlord's Consent to Assignment and Assumption Agreement.

     C.   Landlord has agreed to the terms of this Assignment and has agreed to
execute a written consent agreement (the "Consent Agreement") for this
Assignment.

     NOW THEREFORE, in consideration of the mutual covenants contained in this
Agreement, and for valuable consideration, the receipt and sufficiency of which
are acknowledged by the parties, the parties agree as follows.

     1. Assignment and Assumption. Assignor assigns to Assignee all of its
rights, title and interest to, and under the Lease and the Premises (including
all of Assignor's rights, title, and interest in and to any prepaid rents that
have been paid by Assignor under the Lease for any period before or after the
Effective Date (as defined in Section 10 below) of this Assignment). Subject to
Section 10 hereof, Assignee accepts this assignment, assumes all of Assignor's
rights and obligations under the Lease from and after the Effective Date of the
assignment, and agrees

                                        1

<PAGE>

to be bound by all of the provisions of the Lease and to perform all of the
obligations of the tenant under the Lease as a direct obligation to Landlord
from and after the Effective Date of the assignment. This assignment and
assumption is made on, and is subject to, all of the terms, conditions, and
covenants of this Assignment.

          2. Condition of Premises. The Premises will be delivered by Assignor
to Assignee in good condition and repair, ordinary wear-and-tear excepted, and
in broom-clean condition including all Tenant Improvements constructed under the
Improvement Agreement under the Lease and any Alterations thereafter. All Tenant
Improvements and Alterations shall become the property of Assignee on the
Effective Date of this Assignment, subject to the terms of the Lease.

          3. Assignor's Representations and Warranties. Assignor represents and
warrants that the Premises, the Tenant Improvements and the Alterations are not
subject to any liens, conditional sales contracts, or other encumbrances, except
for any rights the Landlord may have in the Premises, as provided in the Lease.

          Assignor further represents and warrants that:

     .    Assignor is not in default under the Lease as of the time of the
          Effective Date of the Assignment;
     .    Assignor has not stored, deposited or used any toxic or hazardous
          materials on the Premises;
     .    All Tenant Improvements and Alterations on the Premises have been
          approved by the Landlord.
     .    The Lease attached hereto as Exhibit A is a true, accurate, complete
          and up-to-date copy of the lease and all amendments and modifications
          thereto

          4. Obligations of Assignor and Assignee.

a)   Assignor agrees to provide keys and/or cards to the Premises and the
Building on the Effective Date of the Assignment, to pay for all charges for
Operating Expenses (including, but not limited to, CAM's, insurance, taxes and
repairs) up to the Effective Date of the Assignment, and to pay all costs of the
assignment in accordance with the terms of the Lease. Assignor shall promptly
remove its signs from the Premises and from the Building and shall pay for and
repair any damage resulting from said removal. Assignor also agrees to transfer
and assign to Assignee all of its rights, title, and interest in the security
deposit held by the Landlord.

b)   Assignee agrees to reimburse Assignor for Assignee's pro-rata portion of
the January 2002 rent, including the pro rata portion of January Operating
Expenses, for the period of time between the Effective Date and January 31,
2002. Assignee's pro-rata share of the January rent for the Premises shall be
computed based on a monthly rent amount of $22,270.00 and a 31-day month.
Assignee also agrees to reimburse Assignor for the Security Deposit paid by
Assignor in the amount of nineteen thousand five hundred dollars ($19,500.00).
Assignee shall pay the Security Deposit and the pro-rata share of the rent
within thirty (30) days from the Effective Date.

                                        2

<PAGE>

c)   Assignor agrees to defend, indemnify and hold harmless Assignee, its
officers, directors, agents and employees (the "Indemnitees"), from and against
any and all claims, costs and expenses (including reasonable attorney fees)
resulting or arising from any claims by or on behalf of any person(s) or
entity(s), due to the following events or actions occurring prior to the
Effective Date of this Assignment:


     .   Assignor's use, occupancy, or conduct, or any work or thing whatsoever
         done by Assignor in or about, the Premises;

     .   Assignor's use, occupancy, or conduct relating to the Common Areas;

     .   Claims or causes of action arising from any condition of the Premises
         created by Assignor, or arising from any breach or default on the part
         of Assignor in the performance of any covenant pursuant to the terms of
         the Lease;

     .   Claims or causes of action (including, but not limited to, accidents,
         bodily injury (including death) or property damage) arising from any
         acts or omissions of Assignor, or any of Assignor's agents,
         contractors, servants, employees or licensees.

In the event that any action or proceeding is brought against Assignee by reason
of any of the above, Assignee shall promptly notify Assignor, and Assignor
covenants to resist or defend such action or proceeding at Assignor's sole cost,
including settlement costs; provided, however, that Assignee shall have the
right, but not the obligation, to participate in its defense with its own
counsel to the extent Assignee desires and deems appropriate in its sole
discretion.

         5. Further Assurances. Each party to this Assignment will, at its own
cost and expense, execute and deliver such further documents and instruments and
will take such other actions as may be reasonably required or appropriate to
evidence or carry out the intent and purposes of this Assignment.

         6. Entire Assignment; Waiver. This Assignment constitutes the final,
complete and exclusive statement between the parties to this Assignment
pertaining to the terms of Assignor's assignment of the Lease and the Premises
to Assignee, supersedes all prior and contemporaneous understandings or
agreements of the parties, and is binding on and inures to the benefit of their
respective heirs, representatives, successors and assigns. Neither party has
been induced to enter into this Assignment by, nor is either party relying on
any representation or warranty outside those expressly set forth in this
Assignment. Any agreement made after the date of this Assignment is ineffective
to modify, waive, or terminate this Assignment, in whole or in part, unless that
agreement is in writing, is signed by the parties to this Assignment, and
specifically states that the agreement modifies this Assignment.

         7. Governing Law. This Assignment will be governed by, and construed in
accordance with, California Law.

                                        3

<PAGE>

         8.   Captions. Captions to the sections in this Assignment are included
for convenience only and do not modify any of the terms of this Assignment.

         9.   Severability. If any term or provision of this Assignment is, to
any extent, held to be invalid or unenforceable, the remainder of this
Assignment will not be affected, and each term or provision of this Assignment
will be valid and be enforced to the fullest extent permitted by law. If the
application of any term or provision of this Assignment to any person or
circumstances is held to be invalid or unenforceable, the application of that
term or provision to persons or circumstances other than those as to which it is
held invalid or unenforceable, will not be affected, and each term or provision
of this Assignment will be valid and be enforced to the fullest extent permitted
by law.

         10.  Effective Date and Consent of Landlord. The Landlord's and the
Parties' execution of the Consent Agreement is a condition precedent to the
effectiveness and validity of this Assignment. The date of execution by Landlord
and the Parties of Landlord's Consent Agreement shall be the effective date of
this Assignment (the "Effective Date"). If the Landlord and the Parties do not
execute the Consent Agreement, then this Assignment shall not become effective
and shall be null and void.

         11.  Capitalized Terms. All terms spelled with initial capital letters
in this Assignment that are not expressly defined in this Assignment will have
the respective meanings given such terms in the Lease.

         12.  Brokers. The Parties to this Assignment represent and warrant to
each other that neither party dealt with any broker or finder in connection with
the consummation of this Assignment and each Party agrees to protect, defend,
indemnify, and hold the other Party harmless from and against any and all claims
or liabilities for brokerage commissions or finder's fees arising out of that
Party's acts in connection with this Assignment. The provisions of this Section
12 shall survive the expiration or earlier termination of this Assignment and
the Lease.

         13.  Notices. Any notice that may or must be given by either Party
under this Assignment will be delivered (i) personally, (ii) by certified mail,
return receipt requested, or (iii) by a nationally recognized overnight courier,
addressed to the Party to whom it is intended. Any notice given to Assignor or
Assignee shall be sent to the respective address set forth on the signature page
below, or to such other address as that Party may designate for service of
notice by a notice given in accordance with the provision of this Section 13. A
notice sent pursuant to the terms of this Section 13 shall be deemed delivered
(A) when delivery is attempted, if delivered personally, (B) three (3) business
days after deposit into the United States mail, or (C) the day following deposit
with a nationally recognized overnight courier.

         14.  Execution in Counterparts. This Assignment may be executed in any
number of counterparts, each of which when so executed shall be deemed an
original and all of which shall constitute together one and the same instrument,
and shall be effective upon execution by all of the Parties

                                        4

<PAGE>

     IN WITNESS WHEREOF, Assignor and Assignee have executed this Assignment on
the date first written above:


ASSIGNOR:                                           ASSIGNEE:

ELECTRONIC ARTS INC.                                LEAP WIRELESS
                                                    INTERNATIONAL, INC.


By:_______________________________                  By:_________________________

Its:______________________________                  Its:________________________



Address of Assignor:                                Address of Assignee:

209 Redwood Shores Parkway
Redwood City, CA 94065                              10307 Pacific Center Court
                                                    San Diego, CA 92121
                                                    Attn: General Counsel

Attn: General Counsel
                                                    Telephone (858) 882-6000
Telephone: (650) 628-1500

                                        5

<PAGE>

                              EXHIBIT A
                              [Attach Lease and any amendments or modifications]

                                        6

<PAGE>

                  LANDLORD CONSENT TO ASSIGNMENT AND ASSUMPTION

      This Consent is entered into as of the ____ day of ___________, 2002 by
and among EOP-PACIFIC RIDGE CORPORATE CENTRE, L.L.C., a Delaware limited
liability company ("Landlord"), ELECTRONIC ARTS INC., a Delaware corporation
("Assignor") and LEAP WIRELESS INTERNATIONAL, INC., a Delaware corporation
("Assignee").

                                    RECITALS:

A.    Landlord, (as successor in interest to Spieker Properties, L.P.) as
      landlord, and Assignor, as tenant, are parties to that certain Office
      Lease dated September 3, 1999 (the "Office Lease"), as amended by that
      certain First Amendment to Lease dated February 14, 2000 (the "First
      Amendment) (collectively, the "Lease") pursuant to which Landlord has
      leased to Assignor certain premises containing approximately 10,981
      rentable square feet (the "Premises") known as Suite No. 200 on the 2nd
      floor of the building commonly known as Pacific Ridge Corporate Centre and
      located at 5790 Fleet Street, Carlsbad, CA 92008 (the "Building").

B.    Assignor and Assignee have entered into that certain Assignment and
      Assumption of Lease dated January ________, 2002 ("Assignment Agreement")
      attached hereto as Exhibit A whereby Assignor assigned all of its right,
      title and interest in and to the Lease to Assignee.

C.    Assignor and Assignee have requested Landlord's consent to the Assignment
      Agreement and the transaction described therein.

D.    Landlord has agreed to give such consent upon the terms and conditions
      contained in this Consent.

      NOW THEREFORE, in consideration of the foregoing recitals which by this
reference are incorporated herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, Landlord, Assignor and
Assignee agree and represent as follows:

1.    Assignment Agreement. Assignor and Assignee hereby represent and warrant
      that: (a) a true, complete and correct copy of the Assignment Agreement is
      attached hereto as Exhibit A; and (b) the Assignment Agreement fully
      assigns all of Assignor's right, title and interest in the Lease to
      Assignee (the "Transfer").

2.    Representations. Assignor hereby represents and warrants that Assignor (i)
      has full power and authority to assign its entire right, title and
      interest in the Lease to Assignee; (ii) has not transferred or conveyed
      its interest in the Lease to any person or entity, collaterally or
      otherwise; (iii) has full power and authority to enter into the Assignment
      Agreement and this Consent; and (iv) has assigned the entire Security
      Deposit, if any, as described in the Basic Lease Information Section and
      Section 5 of the Office Lease, to Assignee, and Assignor has full power
      and authority to do the same. Assignee hereby represents and warrants that
      Assignee has full power and authority to enter into the Assignment
      Agreement and this Consent.

                                        1

<PAGE>

3.    Assumption. Notwithstanding anything to the contrary contained in the
      Assignment Agreement, Assignee, for itself and its successors and assigns,
      hereby assumes and agrees to perform and be bound by all of the covenants,
      agreements, provisions, conditions and obligations of the tenant under the
      Lease, including but not limited to, the obligation to pay Landlord for
      all adjustments of rent and other additional charges payable pursuant to
      the terms of the Lease. Nothing contained in the Assignment Agreement
      shall be deemed to amend, modify or alter in any way the terms, covenants
      and conditions set forth in the Lease.

4.    No Release. Nothing contained in the Assignment Agreement or this Consent
      shall be construed as relieving or releasing the Assignor from any of its
      obligations under the Lease, and it is expressly understood that Assignor
      shall remain liable for such obligations notwithstanding the subsequent
      assignment(s), sublease(s) or transfer(s) of the interest of the tenant
      under the Lease. Accordingly, notwithstanding anything in the Assignment
      Agreement to the contrary (including, without limitation, the effective
      date thereof), Assignor and Assignee hereby acknowledge and agree that
      both Assignor and Assignee shall be fully responsible for all obligations
      of the tenant under the Lease (regardless of whether such obligations
      accrue prior to or following the effective date of the assignment).

5.    Review Fee. Upon Assignor's execution and delivery of this Consent,
      Assignor shall pay to Landlord the sum of $500.00 in consideration for
      Landlord's review of the Assignment Agreement and preparation of this
      Consent. In addition, within 5 business days of demand by Landlord,
      Assignor shall also pay to Landlord an amount equal to all costs incurred
      by Landlord in connection with considering the request for consent to the
      Assignment Agreement, including without limitation, reasonable attorneys'
      fees.

6.    Landlord's Consent. In reliance upon the agreements and representations
      contained in this Consent, Landlord hereby consents to the Transfer. This
      Consent shall not constitute a waiver of the obligation of the tenant
      under the Lease to obtain the Landlord's consent to any subsequent
      assignment, sublease or other transfer under the Lease, nor shall it
      constitute a waiver of any existing defaults under the Lease. Landlord
      hereby waives Landlord's right to recapture the Premises and cancel the
      Lease under Section 9.2 of the Lease with respect to the assignment of the
      Lease pursuant to the Assignment Agreement.

7.    Insurance. Landlord hereby acknowledges and agrees that so long as the
      coverage afforded Landlord, the other additional insureds and any
      designees of Landlord shall not be reduced or otherwise adversely
      affected, all or part of Tenant's insurance may be carried under a blanket
      policy covering the Premises and any other of Tenant's locations, or by
      means of a so called "Umbrella" policy.

8.    Notice Address. Any notices to Assignee shall be effective when served to
      Assignee at the Premises in accordance with the terms of the Lease. From
      and after the effective date of the Assignment, notices to Assignor shall
      be served at the following address: 209 Redwood Shores Parkway, Redwood
      City, California 94065, Attention: General Counsel.

                                        2

<PAGE>

9.      Deletions. Section 22.1 of the Office Lease (Option to Renew) is hereby
        deleted in its entirety and is of no further force or effect.

10.     Signage. Leap Wireless International, Inc. (i.e., the Assignee named
        herein) and any assignee of the Assignee named herein permitted pursuant
        to the terms of the Lease (and not any sublessee or other transferee of
        the Tenant's interest in the Lease) only shall have the non-exclusive
        right to have a sign ("Tenant's Signage") on the existing monument
        located in the front of the Building (the "Monument"); provided that (i)
        the location of Tenant's Signage shall be for the location of Assignee's
        sign as of the date hereof, (ii) the size, materials, design and all
        other specifications of Tenant's Signage shall be subject to Landlord's
        prior written consent, which consent may be withheld in Landlord's
        reasonable discretion; (iii) Tenant's Sign shall comply with all
        applicable governmental rules and regulations; and (iv) Assignee's
        continuing right to Tenant's Signage shall be contingent on Assignee
        occupying the entire Premises. Landlord shall be responsible for the
        cost of the Monument, and Assignee shall be responsible for all costs
        incurred in connection with the design, construction, installation,
        maintenance and repair, compliance with laws, and removal of Tenant's
        Signage. Notwithstanding anything in the Lease to the contrary, except
        as specifically set forth herein, the tenant under the Lease shall have
        no signage rights at the Building or the Project.

11.     Counterparts. This Consent may be executed in counterparts and shall
        constitute an agreement binding on all parties notwithstanding that all
        parties are not signatories to the original or the same counterpart
        provided that all parties are furnished a copy or copies thereof
        reflecting the signature of all parties.

                                        3

<PAGE>

        IN WITNESS WHEREOF, Landlord, Assignor and Assignee have executed this
Consent on the day and year first above written.

                                   LANDLORD:

                                   EOP-PACIFIC RIDGE CORPORATE CENTRE,
                                   LLC, a Delaware limited liability company

                                      By: EOP Operating Limited Partnership, a
                                          Delaware limited partnership,
                                          its sole member

                                          By: Equity Office Properties Trust, a
                                              Maryland real estate investment
                                              trust,
                                              its general partner

                                              By: ____________________________

                                              Name:___________________________

                                              Title:__________________________



                                   ASSIGNOR:

                                   ELECTRONIC ARTS INC., a Delaware corporation

                                   By:____________________________________

                                   Name:__________________________________

                                   Title:_________________________________

                                   By:____________________________________

                                   Name:__________________________________

                                   Title:_________________________________

                                        4

<PAGE>

                                            ASSIGNEE:

                                            LEAP WIRELESS INTERNATIONAL, INC., a
                                            Delaware corporation

                                            By:________________________________

                                            Name:______________________________

                                            Title:_____________________________

                                            By:________________________________

                                            Name:______________________________

                                            Title:_____________________________

                                        5

<PAGE>

                                    EXHIBIT A

                          COPY OF ASSIGNMENT AGREEMENT

                                   [ATTACHED]

                                        6