Vodafone's shares surged Tuesday following reports that Verizon and AT&T were working on a break-up bid for the British firm.The two US telecoms groups are said to be considering a deal that would see them pay a 40% premium to Vodafone's share price at Monday's close, sources told FT Alphaville. It would put Vodafone's enterprise value at $245bn, making it the biggest merger and acquisition in history.Shares rose 5.06% to 196.0p per share by midday, topping the risers on the FTSE 100.Vodafone has been in the midst of deal speculation in recent months, in relation to the sale of its ownership of a 45% stake in US mobile operator Verizon Wireless.RD