The review is thought to be at an early stage, with BT expected to issue briefs later this week.
The review is expected to cover broadcast and press buying, handled by Starcom, and the online and digital buying handled by Zed Media.
In August, BT appointed Mediaedge:cia to oversee its media planning, having previously handled it inhouse.
Starcom's relationship with BT goes back five years to when it captured the press buying business. Two years ago it landed the TV buying account from The Allmond Partnership, a move which led to the closure of the independent agency.
Zed Media was appointed by BT to its £15 million online business in the summer of 2005 after i-level resigned the account to handle Orange.
Starcom missed out on landing the planning brief when it was resigned by PHD in August 2006 due to conflict with the Omnicom-owned agency's Yell account. Instead, BT recruited the PHD team of Stuart Bowden and Allison Grainger to manage the business as part of the telecoms giant's in-house media department.
BT is currently fighting competition on several fronts as it moves into new business areas. In addition to its fixed line telephony business, BT is spending significant amounts on promoting its broadband service, which dovetails with new product innovations such as its BT Vision TV offering.
Outdoor buying, through Posterscope, is unaffected. Abbott Mead Vickers BBDO continues to handle creative for BT.
Steve Huddleston, the head of media at BT, was unavailable for comment.