I looked into this as I live in the USA and travel to the UK very infrequently. They have done away with you can only roam for so long like four weeks. I have had my sim for over two years and it still works. I just make I have a chargeable text or call every 90 days. I think the time is 180 days, but have to check the T&C to be sure. I used to have Vodaphone until my nephew lost the sim card. I had that for four years with no problem. There is a thread on this in the UK section on
PrePaidGSM.net.