The account is currently split between The Allmond Partnership, which handles buying, and PHD, which handles planning.
O2 had planned to kick off a review this autumn but has put the process back until the first two months of next year.
The mobile company will consider whether to combine planning and buying into one agency. It is not yet known if it will invite non-roster agencies to pitch for the business.
O2's media review follows an overhaul of its other agency relationships.
Vallance Carruthers Coleman Priest was appointed soon after O2 was demerged from BT and the company moved its £20 million direct marketing account into Archibald Ingall Stretton earlier this year.
VCCP's hold on the creative account is unaffected by the media review, which will be the first undertaken by O2 since it launched in November 2001 as part of the newly created MmO2 holding company. TAP and PHD both worked for BT Cellnet before it became O2.
In late 2001, PHD was handed the additional task of co-ordinating O2's pan-European media strategy. This covers O2 operations in The Netherlands, Germany and Ireland.
O2's most recent quarterly figures, issued in July, showed that it had added 258,000 customers to take its total UK customer base to 12.3 million.
O2 was unavailable for comment as Campaign went to press.