A big slice of the lucrative US market is at stake

Vodafone bosses must decide by Friday if they are to join the multi-billion dollar battle.

Speculation about a bid of up to $37bn (�20bn) - topping US rival Cingular's $30bn offer - has raged for weeks.

But Vodafone would have to ditch its 45% stake in US market leader Verizon Wireless if it buys AT&T Wireless.

The decision on whether to buy AT&T Wireless is being seen as a nail-biting one for the board, and especially for Vodafone's recently appointed chief executive Arun Sarin.

Cliff-hanger

Vodafone was reluctant to go into detail about its intentions on Monday morning, limiting itself to a short statement.

"Vodafone Group PLC announces that it continues to monitor developments in the US market and is exploring whether a potential transaction with AT&T Wireless is in the interests of its shareholders," it said.

Sunday newspaper reports suggested the odds in favour of a bid could be 55-45.

AT&T, 16% of which is owned by Japanese giant NTT DoCoMo, could represent a strategic gain for Vodafone by giving it full control of its own US carrier.

The cost of the alternative, buying out its partner Verizon, would probably be prohibitive, and in any case Verizon would be highly unlikely to want to give up its mobile business and limit itself to the mature fixed-line market.

And AT&T's use of the GSM standard - shared by every Vodafone network outside the US and Japan - would mean advanced services and international roaming could be rolled out much quicker.

"The basis of Vodafone's business is that it can develop applications once and roll them out right across its global network," Julian Hewitt at telecoms analysts Ovum told the BBC 's World Business Report.

But still Vodafone may be reluctant to spend so much on a new acquisition which has less reliable network coverage than its current US network.

Shareholders are thought to prefer a period of consolidation, after the �210bn acquisition spree which took place in the late 1990s under its former chief executive, Sir Chris Gent.

And executives have to find a way of making sure they do not shed the Verizon stake, lose out to a rival for AT&T Wireless and end up without a significant US presence.

Vodafone's shares have fallen more than 6% in the last month since the prospect of a bid battle for AT&T Wireless emerged.