The news closely follows speculation that T-Mobile owner Deutsche Telekom is under pressure from key shareholders to either sell or merge its UK business with a rival company.
The telecoms company has also appointed JPMorgan to review options for the future of the UK business after underperforming.
However, it is believed that the deal could be blocked by regulators.
Currently, O2 is the market leader in the UK, followed by Vodafone with a 25% share. T-Mobile has a 15% share and is estimated to be valued between £2.5bn and £3.4bn.
T-Mobile has this year launched high-profile marketing campaigns which have involved a flash mob staged at Liverpool Street tube station and a mass karaoke session at Trafalgar Square.
Meanwhile, Vodafone announced in May that it would accelerate its £1bn cost-cutting plan in response to the weakening European market
The company has posted a pre-tax profit fall of 53.5% to £4.2bn in 2008 compared to £9bn a year earlier.