My 3Uk contract was just about up (hence looking for a phone) but when I crunched the numbers and considered the price I could get for my old phone (via mazuma mobile)the net cost of the the phone was about 225 ukp. (retail, nokia UK, unlocked)

Add that to my existing £10/month contract which includes some textx, calls AND 1Gb FUP data, just paying outright and sticking on my rolling 30 day notice contract is working perfectly.

I'd probably switch to vodafone for best coverage, but 3 have always been the best for openness around data - ie no port blocking, banning of voip/IM etc. Vodafone meanwhile have quite difficult T&Cs prevent use of skype, msn, sip etc etc -- even though they don't really seem to enforce them