An O2 spokesman said the company was expecting to make an announcement on Monday.
The FT reported that the two mobile network operators were in advanced talks to share their networks to save costs. The two are also in negotiations with the government to give up some of the 900Mhz spectrum they own. This would allow others to extend long distance broadband access to more people, especially in rural areas.
However, Vodafone already shares sites, but not equipment, with France Telecom's Orange. Orange spokesmen said the market "could see us open up additional bilateral or multilateral partnerships with other operators". The FT suggested this meant tying up a sharing deal with 3 and T-Mobile.
Network sharing could become the new fashion as the UK moves to implement the aims of the government's Digital Britain report, expected from the end of May. Ofcom is already consulting on whether it should grant BT's Openreach subsidiary, which wholesales BT's network capacity, direct access to the BT network.
A Vodafone spokesman declined to confirm the report. He said, "We regularly review our plans to ensure Vodafone UK is best placed to take advantage of network sharing schemes now and in the future. We will provide any relevant updates as appropriate."