Vodafone Group and Cingular Wireless have started a bidding war for AT&T WIreless, which could take another two weeks to resolve.
Both companies had put in similar bids of around $35bn each.
Bidding had been due to close last Friday, and sources close to the situation said a decision could be expected soon, but AT&T Wireless may now seek a second round of offers from the companies.
Nextel Communications and NTT DoCoMo did not enter bids.
Vodafone has a 45% stake in Verizon Wireless, the largest mobile company in the US. If its AT&T bid proved successful, it would have to relinquish its Verizon stake.
Cingular is a joint venture between SBC Communications and BellSouth, and is the second largest mobile phone company in the US.