<PAGE>

                                                                   Exhibit 10.53


[*] CERTAIN INFORMATION IN THIS EXHIBIT HAS BEEN OMITTED AND FILED SEPARATELY
WITH THE COMMISSION. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED WITH RESPECT
TO THE OMITTED PORTIONS.


                     DEFINITIVE AGREEMENT FOR COLLABORATION

                                   (3G W-CDMA)

THIS DEFINITIVE AGREEMENT (hereinafter referred to as "DA") is made and entered
into this 22nd of October, 2000 by and between UTStarcom Inc., having its
principal place of business at 1275 Harbor Bay Parkway, Suite 100, Alameda,
California 94502, U.S.A. (hereinafter referred to as "UTStarcom") and Mitsubishi
Electric Corporation, acting through its Communication Systems Business
Division, having its principal place of business at 8-1-1, Tsukaguchi-Honmachi,
Amagasaki, Hyogo 661-8661, Japan (hereinafter referred to as "MELCO")



                                WITNESSETH THAT;

WHEREAS, UTStarcom and MELCO (hereinafter referred to individually as a "Party"
and collectively as "Parties") have a strong intention to establish a mutually
beneficial business relationship, bringing the expertise and experiences of each
Party in China and other Asian market (hereinafter referred to as "Territory");
and

WHEREAS, UTStarcom and MELCO have concluded MEMORANDUM OF UNDERSTANDING (MoU)
(3G W-CDMA) on March 31, 2000; and

WHEREAS, UTStarcom and MELCO have concluded Joint Development Plan on June
21, 2000:

WHEREAS, The Parties have studied the business and technical feasibility of
development of 3G W-CDMA in [*] based on UTStarcom WACOS platform (hereinafter
referred to "WACOS 3G Network") in accordance with MOU:

NOW, THEREFORE, in the light of the above recitals, the Parties hereto set forth
the DA, as follows:

1.   SCOPE OF WORK FOR THE DEVELOPMENT, TIME FRAME OF MAJOR MILESTONE AND ROLE &
     RESPONSIBILITY OF PRODUCT DEVELOPMENT AND SYSTEM INTEGRATION & TESTING

     The Parties confirm to jointly develop and market a complete suite of
     infrastructure product for the 3rd generation cellular network (hereinafter
     referred to as "3G W-CDMA") with a spirit of creating and developing a new
     business based on Parties' own initiated architecture and specification in
     [*]. MELCO will develop 3G BTS and UTStarcom will develop the rest of the
     network infrastructures (RNC, MSC/GSN, NMS, etc.) of a 3G W-CDMA based on
     WACOS platform (hereinafter referred to as "the Products").

     Scope of work for development, Time frame of major milestone and Role &
     Responsibility of product development and system integration & Testing are
     described in Annex-1 (UTStarcom & Mitsubishi 3G Joint Development Plan).
<PAGE>

     The Parties shall jointly perform system integration effort in accordance
     with Addendum-1.

2.   TASK FORCE TEAM AND STEERING COMMITTEE

     During the term of this DA, the Parties internally promote their
     cooperation with all reasonable means with the aim to secure a satisfactory
     result of this DA. The Parties shall carry out and complete the development
     of the respective products with the Parties' due diligence for a joint
     business development. The Parties organize the following:

     (1) Task Force

         a.   A task force composed of two teams, one business and one
              technical, from each Party is hereby created. Each Party shall
              assign a task force leader to be in charge of ensuring the proper
              implementation of the DA and, in particular, the coordination of
              each Party's task. The names of these individuals are listed in
              Annex 2.

              The technical task force will be responsible for the execution of
              the engineering development. The business task force will be
              responsible for the execution of business development.

         b.   Task force shall meet on a regular basis, in principle once a
              month.

         c.   Important agreed decisions shall be recorded in writing and signed
              by the task force. Such signed writing shall serve as the records
              of the DA implementation.

         d.   In the event of disagreement, the task force will escalate the
              issue to the Steering Committee.

     (2) Steering Committee

         a.   The Parties create a Steering Committee including the management
              of each Party and other staff member directly involved in the
              Project as per Annex-3.

         b.   The Steering Committee shall meet regularly on quarterly basis
              unless either Party call for an extraordinary meeting for a
              purpose of management review and important decision making,
              including schedule and role & responsibility, as well as an
              effectual business development.

         c.   Decision of the Steering Committee shall be made by the Parties'
              mutual agreement. At the conclusion of each meeting, the
              representatives shall prepare minutes and sign the same.

         d.   The Steering Committee shall examine and make decisions on all
              important matters relating to this DA, including, but not limited
              to:

                  i.       Winning strategy for proactively obtaining 3G W-CDMA
                           business.

                                      -2-
<PAGE>

                  ii.      Review of implementation and execution of D/A.

                  iii.     Review of analysis of competition and carriers'
                           network planning for 3G, financial back up for 3G
                           implementation and carriers' preference of technology
                           for 3G and set an action plan to be taken.

                  iv.      All important questions raised by the task force and
                           the decisions to be made in respect thereof.

3.   COST [*]

     [*] shall bear [*] cost incurred during the system integration, in
     particular, for integration testing during the [*] phases as shown in
     Annex-4, unless otherwise agreed in this DA or separately.

     If the quantity shown in Annex-4 will be increased in future, the Parties
     shall discuss [*] with regard to extra-cost to be caused by the increase of
     the quantity.

     In the event that either Party requires support from the other party for
     successful development and execution of respective responsible portion, the
     other Party may support the requesting Party on the basis of [*].

4.   3G MOBILE SIMULATOR

     MELCO shall provide 3G mobile simulator during the [*] phases if UTStarcom
     requests for it. The quantity will be further discussed.

5.   [*] TERMS/CONDITIONS

     UTStarcom shall have the right to sell the MELCO BTS on [*] basis to
     UTStarcom's customers [*] under the condition that the BTS is still
     manufactured by MELCO.

     MELCO shall have the right to sell the UTStarcom RNC and WACOS 3G products
     on [*] basis to customers [*] under the condition that the RNC and WACOS 3G
     products are still manufactured by UTStarcom.

     In the event that MELCO or its nominees arrange Official Development Aids
     (ODA) or equivalent financing, and the financing requires MELCO's brand
     name on the MELCO BTS, UTStarcom shall use MELCO's brand name on the BTS
     for commercial proposals and any associated contracts.

     In the event that a joint venture is established between UTStarcom and
     MELCO after completion of a joint-venture feasibility study, MELCO's supply
     of the MELCO BTS to UTStarcom on [*] basis will be re-studied and
     negotiated to mutual agreement between the Parties.

                                      -3-
<PAGE>

6.   COLLABORATION OF SYSTEM INTEGRATION

     UTStarcom and MELCO shall collaborate in the system integration using
     MELCO's BTS together with UTStarcom's RNC and WACOS 3G Core Network
     products as per conditions stipulated in Addendum-1.

7.   RELEASE OF INFORMATION

     (1) UTStarcom will provide MELCO with necessary and sufficient information
         and data to the extent available, subject to Article 13(4), for MELCO's
         timely study upon MELCO's request.

     (2) MELCO will provide UTStarcom with necessary and sufficient information
         and data to the extent available, subject to Article 13(4), for
         UTStarcom's timely study upon UTStarcom's request.

8.   SUBCONTRACTING

     Subject to the stipulation set forth in the DA, each Party shall be
     entitled to subcontract, at its own risk, to a corporation or corporations
     of its choice, any part of the supplies and services allocated to it under
     this DA.

9.   PARTICIPATION OF THIRD PARTY INTO JOINT DEVELOPMENT

     UTStarcom and MELCO agree to consider a participation of an appropriate
     third company in the joint development, in case both Parties mutually judge
     that the participation of the third Party will enhance the Parties strength
     of competitiveness and a probability to win any bid in the Territory in the
     future. In such a case, the items stated in this DA shall still hold valid
     between UTStarcom and MELCO; and a separate agreement will be made among
     all Parties, reflecting this DA.

10.  PURCHASE WARRANTY

     The Parties shall honor Clause 7 of MOU signed on March 31, 2000, as it is
     clearly stipulated as a legal binding Clause in Clause 16(3) of the MOU.
     [*] shall retain the sole discretion of whether MELCO's BTS is equal or
     better than that of another vendor in terms of price, quality,
     functionality and performance, in a reasonable and fair manner with good
     faith.

     If MELCO BTS satisfies the requirements of potential customers in terms of
     technical performance (by the sole discretion of [*] in a reasonable and
     fair manner with good faith), and MELCO's price is equal or better than
     other competing BTS units (by the sole discretion of [*] in a reasonable
     and fair manner with good faith), UTStarcom shall in the best effort
     purchase [*] of UTStarcom BTS product needs from MELCO.

11.   [*]


                                      -4-
<PAGE>

12.  DISPUTES

     All disputes, controversies or differences which may arise between the
     Parties hereto, of or in relation to or in connection with this DA, whether
     during or after its term, which fails to be solved amicably, shall be
     finally resolved by arbitration in accordance with the Rules of
     Conciliation and Arbitration of the International Chamber of Commerce as in
     force on the date of this DA. The arbitration shall be held in (a) Tokyo,
     Japan in case of an arbitration claim filed by UTStarcom; and in (b) New
     York, USA in case of an arbitration claim filed by MELCO. The arbitration
     panel shall consist of three (3) arbitrators appointed in accordance with
     the said Rules. All arbitration proceeding shall be conducted in English
     language.

13.  CONFIDENTIALITY AND INDUSTRIAL AND/OR INTELLECTUAL PROPERTY

     (1) Ownership of Intellectual Property

         The Parties agree that each Party retains full and exclusive rights and
         ownership in any and all letters patent, inventions, software,
         algorithms, know-how, trademarks, copyrights and trade secrets, and any
         other proprietary rights which the Party currently possess, or develop
         independently pursuant to this DA.

     (2) Joint Invention

         It is not anticipated that the Parties shall carry out joint
         development work, but in the event that the personnel of MELCO and
         UTStarcom jointly make an invention or generate intellectual property
         rights in the course of the development, the Parties shall jointly file
         an application and have the right to use such intellectual property
         right without accounting to the other. Expenses incurred in connection
         with the filing and maintenance of the protective rights shall be
         shared equally, unless a Party elects not to file an application, in
         which case the other Party may file at its own expense and enjoy the
         exclusive ownership.

     (3) Against Infringement

         In the event a claim is brought by a third party alleging that the
         Products infringe any patent, copyright or any other intellectual
         property right of that third party, the Party having supplied the
         infringing module shall defend and settle the claim and indemnify and
         hold the other Party harmless from any fees, expenses or damages that
         may be incurred or awarded as consequence of such claim.

     (4) Confidentiality

         "Confidential Information" is all information (i) identified in written
         or oral format by the Disclosing Party as confidential, trade secret or
         proprietary information, and, if disclosed orally, summarized in
         written format within thirty (30) days of disclosure. "Disclosing
         Party" is the Party disclosing Confidential Information. "Receiving
         Party" is the Party receiving Confidential Information.

                                      -5-
<PAGE>

         The Receiving Party may use the Confidential Information solely for the
         purpose of joint development of 3G W-CDMA. The Receiving Party shall
         not disclose the Confidential Information to any third party other than
         persons in the direct employ of the Receiving Party and its
         subsidiaries who have a need to have access to and knowledge of the
         Confidential Information solely for the purpose authorized above. Each
         Party shall take appropriate measures by instruction and agreement
         prior to disclosure to such employees to assure against unauthorized
         use or disclosure.

         The Receiving Party shall have no obligation with respect to
         information which (i) was rightfully in possession of or known to the
         Receiving Party without any obligation of confidentiality prior to
         receiving it from the Disclosing Party; (ii) is, or subsequently
         becomes, legally and publicly available without breach of this
         Agreement; (iii) is rightfully obtained by the Receiving Party from a
         source other than the Disclosing Party without any obligation of
         confidentiality; (iv) is developed by or for the Receiving Party
         without use of the Confidential Information and such independent
         development can be shown by documentary evidence; (v) becomes available
         to the Receiving Party by wholly lawful inspection or analysis of
         products offered for sale; (vi) is transmitted by a Party after
         receiving written notification from the other Party that it does not
         desire to receive any further Confidential Information; (vii) is
         disclosed by the Receiving Party pursuant to a valid order issued by a
         court or government agency, provided that the Receiving Party provides
         (a) prior written notice to the Disclosing Party of such obligation and
         (b) the opportunity to oppose such disclosure.

         Upon written demand by the Disclosing Party, the Receiving Party shall:
         (i) cease using the Confidential Information, (ii) return the
         Confidential Information and all copies, notes or extracts thereof to
         the Disclosing Party within [*] of receipt of demand, and (iii) upon
         request of the Disclosing Party, certify in writing that the Receiving
         Party has complied with the obligations set forth in this paragraph.

         The terms of confidentiality under this Agreement shall not be
         construed to limit either Party's right to independently develop or
         acquire products without use of the other Party's Confidential
         Information. The Disclosing Party acknowledges that the Receiving Party
         may currently or in the future be developing information internally, or
         receiving information from other parties, that is similar to the
         Confidential Information. Accordingly, nothing in this Agreement will
         be construed as a representation or agreement that the Receiving Party
         will not develop or have developed for it products, concepts, systems
         or techniques that are similar to or compete with the products,
         concepts, systems or techniques contemplated by or embodied in the
         Confidential Information provided that the Receiving Party does not
         violate any of its obligations under this Agreement in connection with
         such development.

         Notwithstanding anything herein contained to the contrary, each Party
         shall have the right to refuse to receive any Confidential Information,
         and the right to use Residuals for any purpose, including, but not
         limited to use in development, manufacture, promotion, sale and
         maintenance of its products and services, without paying any charge to
         the Disclosing Party, provided that each Party shall maintain the
         confidentiality as provided herein and that the right to Residuals does
         not represent a license under any patent right, utility model right,

                                      -6-
<PAGE>

         design right or trade mark right of the Disclosing Party. The term
         "Residuals" means information in non-tangible form retained in the
         unaided memories of the Receiving Party's and its subsidiaries'
         employees who have had rightful access to the Disclosing Party's
         Confidential Information pursuant to the term of this Agreement. An
         employee's memory is unaided if the employee has not intentionally
         memorized the Confidential Information for the purpose of retaining and
         subsequently using or disclosing it. Both Parties agree that any
         Confidential Information disclosed hereunder by the other Party in the
         course of performance of the subject matter provided hereunder shall be
         considered as Residuals.

         Each Party shall retain all right, title and interest to such Party's
         Confidential Information. No license under any trademark, patent or
         copyright, or application for same which are now or thereafter may be
         obtained by such Party is either granted or implied by the conveying of
         Confidential Information.

         The Receiving Party shall not reverse-engineer, decompile, or
         disassemble any software disclosed to it and shall not remove,
         overprint or deface any notice of copyright, trademark, logo, legend,
         or other notices of ownership from any originals or copies of
         Confidential Information it obtains from the Disclosing Party.

         CONFIDENTIAL INFORMATION IS PROVIDED "AS IS" WITH ALL FAULTS. IN NO
         EVENT SHALL THE DISCLOSING PARTY BE LIABLE FOR THE ACCURACY OR
         COMPLETENESS OF THE CONFIDENTIAL INFORMATION.

         None of the Confidential Information disclosed by the Parties
         constitutes any representation, warranty, assurance, guarantee or
         inducement by either Party to the other with respect to the
         infringement of trademarks, patents, copyrights; any right of privacy;
         or any rights of third persons.

         Neither Party shall transmit, directly or indirectly, the Confidential
         Information or any technical data received from the other Party, nor
         the direct product thereof, without the Disclosing Party's prior
         written consent and in accordance with all export laws and regulations
         of the United States and Japan. The Parties agree that they do not
         intend nor will they, directly or indirectly, export or re-export any
         Confidential Information to any end-user who either Party knows or has
         reason to know will utilize it in the design, development or production
         of nuclear, chemical or biological weapons or to any end user who has
         been prohibited from participating in U.S. and Japanese export
         transactions by any federal agency of the U.S. and Japanese Government.

         Each Party acknowledges that monetary remedies may be inadequate to
         protect Confidential Information and that injunctive relief may be
         appropriate to protect such Confidential Information.

         Not withstanding the foregoing sentence, each Party may disclose joint
         developed Interface specification between MELCO's 3G BTS and
         UTStarcom's WACOS PNC and Interface specification between MELCO's 3G
         BTS and UTStarcom's WACOS Network Management Center to third party who
         agree in writing to be bound by the provisions hereof, provided that

                                      -7-
<PAGE>

         the third party shall not disclose the specifications to any other
         party. The Parties shall take every reasonable precaution to protect
         the confidentiality of Confidential Information or materials to be
         confidential. In the event of termination of this DA, there shall be no
         use or disclosure by either Party of any Confidential Information of
         the other Party, and neither Party shall manufacture or have
         manufactured any product, devices, components or assemblies utilizing
         any of the other Party's Confidential Information absent a prior
         written agreement between the Parties. Additionally, neither Party
         shall use the name of the other party in any news release, public
         announcement, advertisement or other form of publicity without the
         prior written consent of the other Party.

14.  EFFECTIVE DATE -- TERM

     This DA comes into force as soon as it is signed by the Parties and shall
     remain valid until December 31st, 2002 or the date to be mutually agreed.
     Within [*] before December 31st, 2002 or the date extended by mutual
     agreement, the Steering Committee shall decide on the future course of the
     cooperation or extension of this DA.

15.  ASSIGNMENT

     Both parties [*] the right to assign or transfer any or all of its rights
     and obligations under this DA to any third party without the prior written
     agreement of the other Parties.

16.  TERMINATION OF THE AGREEMENT AND INDEMNIFICATION

     Either Party shall have the right to terminate this DA for default by the
     other in performance of any substantial obligation or material breach of
     this DA where such default or breach continues for a period of [*] after
     written notice thereof to the defaulting Party.

     In case this DA is terminated, as per this clause, the defaulting party
     shall be responsible for the compensation of the direct loss, which the
     other party may suffer because of the termination of this DA. In any case,
     the Parties shall not be responsible for each other for indirect and/or
     consequential loss.

17.  GOVERNING LAW

     This DA shall be construed in accordance with the laws of New York State,
     USA.

18.  COMMUNICATIONS-ADVERTISING

     (1) Both parties shall not make any announcement or communicate any
         information to a third party concerning the purpose of this DA without
         the prior approval of the other Party, except as may be required by
         applicable law.
     (2) Any advertising by one Party shall make reference to the other Party.
     (3) Public announcement and/or press release related to this DA will be
         done at appropriate time subject to the agreement by the Parties.

                                      -8-
<PAGE>

19.  OTHERS

     (1) Headings
         Headings to articles of this DA are to facilitate reference only, do
         not form a part of this DA, and shall in no way affect its
         interpretation.

     (2) Entire Agreement
         This DA represents the entire agreement between the Parties regarding
         its subject matter superseding previous communications or
         understandings. This DA may not be modified except by written approval
         by the Parties.

     (3) Partnership disclaimer
         In principle, the relationship of UTStarcom and MELCO established by
         this DA shall be that of prime contractor and key subcontractor as a
         team member, and nothing contained in this DA shall be construed:
         i.     to give either Party the power to direct or control the day-to-
                day activities of the other or:
         ii.    to constitute the Parties as partners, joint venture, co-owner
                or otherwise as participants in a joint or common undertaking.

20.  EFFECTIVENESS OF AGREEMENT

     This agreement is legally binding, but subject to final legal rewording.


                                      -9-
<PAGE>



IN WITNESS WHEREOF, The Parties hereto have caused their representatives, duly
executed in two (2) original copies by their duly authorized representative.


UTStarcom Inc                              Mitsubishi Electric Corporation





By:                                   By:
   ------------------------------          -------------------------------------

Name: Hong Liang Lu                        Name: Teruhiko Moriyama

Title: President and CEO                   Title: Division President
                                                  Communication Systems Business
                                                  Division

Date: October 22, 2000                     Date:  October 22, 2000
     ----------------------------               --------------------------------




                                      -10-
<PAGE>

ANNEX-1



Refer to the Joint Development Plan signed by MELCO and UTStarcom on Jun-21,
2000.



<PAGE>

ANNEX-2



MELCO TASK FORCE TEAM

-    Lead:
         M. Todo, Group Manager,
         International Marketing & Business Development Department

-    Technical:
         K. Mihashi, Project Manager,
         H. Kojima, Manager,
         Mobile Communication Network Systems Department

-    Business:
         T. Aoki, Senior Manager,
         International Marketing & Business Development Department



UTSTARCOM TASK FORCE TEAM

-    Lead:            Pat Chan, Director, Mobile Network

-    Technical:       Phil Lee, System Project Manager,

-    Business:        Jack Wu, Director, Product Management



<PAGE>

ANNEX-3


MELCO STEERING COMMITTEE MEMBERS:

T. Moriyama:               Division President
                           Communication Systems Business Division

K. Teshima:                Deputy Division President
                           Communication Systems Business Division
                           Carrier Network Systems Business Center

S. Aoyama:                 General Manager
                           Communication System R&D Center

K. Kimura:                 General Manager
                           Mobile Communication Network Systems Department

T. Kanamori:               General Manager
                           International Marketing & Business Development
                           Department

M. Todo:                   Group Manager,
                           International Marketing & Business Development
                           Department


UTSTARCOM STEERING COMMITTEE MEMBERS:

Hong Lu:                   President and CEO

Bill Huang:                Vice President
                           Chief Technology Officer

Pat Chan:                  Director, Mobile Network

Jack Wu:                   Director, Product Management



<PAGE>

ANNEX-4



SYSTEM INTEGRATION CORE NETWORK/RNC & UE/BTS REQUIREMENT




(1) For System Integration [*]

              [*]


(2) For Debug [*]


              [*]



<PAGE>


ADDENDUM-1



1.   SYSTEM INTEGRATION DEVELOPMENT EFFORTS FOR RNC AND BTS UNITS:

a.   The Parties shall jointly develop a complete suite of infrastructure
     products for 3G cellular network based on each Parties' own initiated
     architecture and specifications. MELCO will develop a 3G BTS, and UTStarcom
     will develop a RNC based upon the UTStarcom WACOS product platform.
b.   The Parties shall collaborate as to the development of the Interface
     specifications between the BTS and RNC units ("Iub").
c.   MELCO shall develop the BTS in accordance with Iub. UTStarcom shall develop
     the RNC unit which will function with MELCO BTS in accordance with Iub.
d.   UTStarcom shall be responsible for developing, producing and supplying the
     RNC by itself without MELCO's engineering support; except for Iub interface
     for BTS and RNC which is under joint development with MELCO's initiative.
e.   Upon the request of MELCO, and after payment to UTStarcom as stipulated in
     Item 2 below, UTStarcom shall provide MELCO with necessary assistance as to
     UTStarcom RNC for MELCO proposals to potential customers for implementation
     of the UTStarcom RNC with MELCO's BTS and UTStarcom 3G Core Network.
f.   MELCO will provide BTS for UTStarcom primarily for [*] market where
     UTStarcom can lead marketing of W-CDMA infrastructure, while UTStarcom
     shall provide RNC for MELCO where MELCO can lead marketing of W-CDMA
     infrastructure. Conditions of Agreement shall be mutually agreed upon.



2.   PAYMENT TERMS:

In consideration that
     (1) UTStarcom having a joint integration with MELCO's BTS and providing
         MELCO the binary software of the RNC, together with the associated
         documents to MELCO. The documents shall include: Specification of WACOS
         and Basic Specification of RNC by [*]; Specification and Drawing of RNC
         by [*]; and binary RNC software and Operation Manual of RNC by [*]
         (worth of [*]);
     (2) UTStarcom providing one set of RNC and WACOS 3G products to MELCO as
         test bench after the [*] (worth of [*]);
     (3) Upgrading (2) to General Availability (GA) version (worth of [*])

MELCO will pay the following amounts under the following terms and conditions as
mentioned in Item 3 of the Addendum-1.

     a.  Total Payment Amount: [*]
<PAGE>

     b.  Terms of payment:

              1st payment: [*] within [*] after the signing of this DA, MELCO's
                  receipt of UTStarcom development plan and its official
                  notification of authorized fund amount.

              2nd payment: [*] within [*] after the mutual confirmation of
                  successful [*] demonstration of RNC functionality with BTS on
                  the Iub interface.

              3rd payment: [*] within [*] after MELCO's receipt of a delivery
                  acceptance confirmation of a UTStarcom RNC by a customer in
                  accordance with a UTStarcom contract to be signed with a
                  customer for 3G W-CDMA including MELCO's BTS.

3.   MARKETING TERMS/CONDITIONS:

UTStarcom shall pay to MELCO [*] of RNC selling price [*] under the condition
that the sold 3G system will use a third party BTS.

                                      -2-