Here is a nice link for any Brits that go home fairly often and have a UK address, T-Mobile uk is offering free pay as you go sim cards (2 per household) and they have 3 different plans, for all networks it is 15p min, they also have a 5 day unlimited web n walk for £2.50, I have just ordered 2 cards, so hopefully they will be waiting for me when I get home, and as I also have a spare unlocked phone I can lend the Uk Phone to friends when they go home, along with the oyster card.