In a statement, BT said: “We have received expressions of interest from shareholders in two UK mobile network operators, of which one is O2, about a possible transaction in which BT would acquire their UK mobile business.
“All discussions are at a highly preliminary stage and there can be no certainty that any transaction will occur.”
O2 used to be called BT Cellnet, before it relaunched on 2002.
This comes as BT teams with EE to launch its own consumer mobile service, which will allow it to provide bundles of phone, Internet and TV service.
It has also been said that BT will provide broadband access to EE and Vodafone Group Plc so that they can offer their own packages.