I switched from O2 PAYG here in the UK to T-mobile to get on the Mobile Phones Direct contract deal (700 mins, unlimited text and 1GB fair use internet a month) for £35.

Generally, very happy, 3g data is generally faster and more reliable on T-mobile (I think it's all the iphone users on O2 sucking up the bandwidth) but the real annoying thing is that the one place I can't get a signal on T-mobile is my house - well, not completely true, I can't get a signal on the first 2 floors but if I go up to my attic I get a wonderful signal! On O2 I always had a great signal in my house...

My hope is that when T-mobile merge with Orange I might begin to get a better signal