Odds are on Vodafone, 3, O2 or anyone else who may or may not offer an unlimited 3G data plan are going to either put an explicit prohibition or cap on the amount of data you can use in a billing cycle unless they’ve anticipated a product like this in their plans.

The market for 3G as a broadband alternative is also likely a relatively small one. From what I have seen European carriers have done a better job in rolling out DSL to exchanges which serve smaller markets than carriers in the United States.