I am a Cingular subscriber in the U.S. and have a Motorola V400 GSM phone. Cingular claims that I have the ability to roam in the UK (apparently using the Vodaphone network), using my U.S. phone number, for which I will be charged US$1.29 for incoming and outgoing calls. Alternatively, they tell me that I can purchase a pre-paid SIM card in the UK, which may allow me to use my phone more cheaply.

Any views or comments on this? Does this sound right? I arrive at LHR at about 8:00pm on a Sundy night. Might there be someplace at LHR that I could buy one of these pre-paid SIM cards at LHR, or once I get into central London, at that hour on a Sunday?