Exhibit 31.2




CERTIFICATION




I, Peter Kelly, certify that:




1.I have reviewed this annual report on Form 10-K of Agere
Systems Inc.;




2.Based on my knowledge, this report does not contain any
untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which
such statements were made, not misleading with respect to the period covered by this report;




3.Based on my knowledge, the financial statements, and
other financial information included in this annual report, fairly present in all material respects the financial condition, results of operations and
cash flows of the registrant as of, and for, the periods presented in this report;




4.The registrants other certifying officers and I are
responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal
control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:




(a)Designed such disclosure
controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information
relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the
period in which this report is being prepared;




(b)Designed such internal control
over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable
assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with
generally accepted accounting principles;




(c)Evaluated the effectiveness of
the registrants disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure
controls and procedures, as of the end of the period covered by this report based on such evaluation; and




(d)Disclosed in this report any
change in the registrants internal control over financial reporting that occurred during the registrants most recent fiscal quarter (the
registrants fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect,
the registrants internal control over financial reporting; and




5.The registrants other certifying officers and I
have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrants auditors and the audit
committee of the registrants board of directors (or persons performing the equivalent functions):




(a)All significant deficiencies
and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the
registrants ability to record, process, summarize and report financial information; and




(b)Any fraud, whether or not
material, that involves management or other employees who have a significant role in the registrants internal control over financial
reporting.




Date: December 9, 2005




/s/ Peter KellyPeter Kelly Chief Financial Officer


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