The telecoms company told the City that it does not intend to make an offer for Vodafone - dashing months of talk about a potential combination.
The speculation peaked at the World Economic Forum in Davos, Switzerland, last week when Randall Stephenson, AT&T's chairman and chief executive, met EU telecoms commissioner Neelie Kroes. It is thought they discussed AT&T's ambition to become a major player in the European market.
Mr Stephenson fuelled his company's potential links to Vodafone or British rival EE by saying in November that he was excited by the "huge opportunity" to invest in mobile broadband in Europe.
Speculation over a potential bid has also intensified as Vodafone nears completion on the £84 billion sale of its share in Verizon Wireless.
The bulk of the proceeds will go to Vodafone shareholders, while the Berkshire-based company plans to plough £7 billion into organic investment, including in boosting its 4G, 3G, fibre and broadband services.
The Verizon deal is expected to complete next month, with Vodafone shareholders due to vote on the US sale at a special meeting tomorrow.
A combination with AT&T would have created a telecoms giant with a market value in the region of £150 billion. Under takeover rules, AT&T is now prevented from making a move for Vodafone for six months, unless another party tables an offer for the UK company in the meantime.