Try t-mobile....we have a web n walk pro package added to our pay monthly phone contract....it costs £10/month for unlimited use (they suggest 2gb as the fair use limit) the only drawback is you cant use skype(voip) or msn messenger etc. we have Nokia N70's and connect to a mac and a pc via bluetooth with no problems. It uses 3g where available and gprs the rest of the time......works well...am typing this with just one bar on the signal strength at the moment although its quicker with more bars! T-mobile also do a data card for £19/month on a 18 month contract.
Cheers
Gareth
PS and you get a good service in Braunston!!!
PPS The phone add on package we have is not mentioned on the t-mobile website...you need to talk to a good dealer or t-mobile direct