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Exhibit 10.51 FIRST AMENDING AGREEMENT
TO
AMENDED AND RESTATED MASTER CONTRACT MANUFACTURING
SERVICES AGREEMENT THIS FIRST AMENDING AGREEMENT TO AMENDED AND RESTATED MASTER CONTRACT MANUFACTURING SERVICES
AGREEMENT (Amendment) is entered into between Nortel Networks Limited, a Canadian corporation
with a place of business at 8200 Dixie Road, Suite 100, Brampton, Ontario L6T 5P6 (NNL) and
Flextronics Telecom Systems, Ltd., a company organized under the laws of Mauritius (FTS), and
shall be effective as of November 1, 2004 (Effective Date). WHEREAS, NNL and FTS (the Parties) entered into an Asset Purchase Agreement dated as of June 29,
2004 (the APA), whereby NNL agreed to sell and FTS agreed to purchase certain assets for the
purpose of transferring, inter alia,the Operations, as that term is defined in the APA, of the
Montreal OPTO 1 Facility (as that term is defined in the APA) located in Montreal, Quebec; AND WHEREAS, the Parties also entered into an Amended and Restated Master Contract Manufacturing
Services Agreement dated as of June 29, 2004, (the MCMSA) whereby NNL agreed to purchase and FTS
agreed to provide, or cause it affiliates to provide, certain manufacturing and design services; AND WHEREAS, the Parties also agreed that the commencement of those design services related to
NNLs Optical products would be concurrent with the transfer of the Montreal OPTO 1 Facility, which
the parties anticipated would take place on November 1, 2004; AND WHEREAS, the Parties have subsequently agreed that the Montreal OPTO 1 Facility will transfer
at a date later than November 1, 2004 while the resources and assets related to the Design
Operations (as that term is defined in the APA) will transfer on November 1, 2004, and NNL wishes
to purchase design services from FTS or its affiliates as of November 1, 2004; and AND WHEREAS, NNL and FTS wish to amend the MCMSA to reflect the distinction between the dates of
the commencement of the Optical design services and the transfer of the Montreal OPTO 1 Facility,
as well as to correct some drafting errors in the MCMSA. NOW, THEREFORE, in consideration of the mutual promises hereinafter set forth (the receipt and
sufficiency of which is hereby acknowledged), the Parties hereby agree as follows: 1.      Except as expressly defined herein or by reference to definitions in the APA, the words used as
defined terms in the First Amending Agreement shall have the same meaning and effect as those set
definitions set forth in Exhibit 1 to the MCMSA. 30/04/03 1st Amending Agreement  Flextronics 1




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2.      The fourth sentence of the Preamble of the MCMSA shall be deleted and replaced as
follows;  This Agreement will come into effect with respect to Exhibits 9-1 and 9-2 on
November 1, 2004. 3.      Section 6.1 of the MCMSA shall be amended to delete the phrase During the first 3
years of the Amended Term which appears at the beginning of the second and fourth
paragraphs of Section 6.1 and to replace this phrase with For the period of 3 years
following the transfer of design resources on November 1, 2004. 4.      Exhibit 9-1 and Exhibit 9-2 attached to the MCMSA shall be amended to replace all
instances of the phrase St. Laurent VSHA Effective Date with the phrase November 1,
2004, except for the reference in paragraph 47 of Exhibit 9-2, which shall be February
1, 2005. 5.      Section 4.7 of the MCMSA shall be amended to replace the phrase Nortel Networks
Flextronics with Nortel Networks Vendor in the last sentence. 6.      Section 6.1 of the MCMSA shall be amended with respect to the list of the manufacture
discontinued Optical products for which Flextronics will provide design services and
shall now read TN-16X, TN-4X, OC-12, OC-48 and OC-192. 7.      Exhibit 17-2 shall be amended to replace the first sentence of Section 3.0 (C) with
the following:  Flextronics shall identify design cost reduction programs relating to the Products
associated with each respective System House within 6 months after the transition of
the applicable System House to be eligible for ICR; provided that such programs may
not conflict with the Nortel Networks programs identified in Appendix B and such
programs must be substantially implemented by Flextronics resources that are
incremental to the design resources transferred to Flextronics by Nortel Networks. 8.      Exhibit 17-2 shall also be amended to such that Section 5.0 shall now read as
follows:  5.0    Nortel Networks DCRs
Appendix B to this Exhibit 17-2 lists the DCRs planned by Nortel Networks as of
November 15, 2004. The Parties may amend this list per the ICR Change Management
Process. 9.      All other terms and conditions of the MCMSA shall remain unchanged; nothing herein shall be
construed as relieving either party of any right or obligation under the MCMSA except as expressly
set forth herein. 30/04/03 1st Amending Agreement  Flextronics 2




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IN WITNESS WHEREOF, the parties hereto have signed this First Amending Agreement to the Amended and
Restated Master Contract Manufacturing Services Agreement by their duly authorized representatives,
to be effective as of the Effective Date first above written, although actually signed by the
parties on the dates shown below their respective signatures. NORTEL NETWORKS LIMITED
    
    FLEXTRONICS TELECOM SYSTEMS, LTD.By: /s/ C. Bolouri
    
    By: /s/ M. MarimuthuName: Chahram Bolouri
Title: President, Global Operations
    
    Name: Manny Marimuthu
Title: DirectorDate:
    
    Date:
 30/04/03 1st Amending Agreement  Flextronics 3