Note: I was in Covent Garden today and the T-Mobile one said that you would not use credit if you used your phone at least every 180 days. Since their pre-paid allows roaming, you just need to do something with the phone in their roaming area... I suggest just sending a text message, as that's only 35p when roaming in most places.

I keep a spare Virgin SIM for friends visiting. What a easy way to keep in touch.

Timothy