Wot Tom said...
My phone (Samsung Tocco) supports data speeds up to 7.2Mbs (not that my network does, but hey-ho). So I just pay for the web bolt-on from O2 for £7.50 per month and use my phone as a bluetooth modem. It's technically against the terms of service to do this, but it's my understanding that it's pretty impossible to detect if all you're doing is browsing the web.