OK, spoke to the technical guy on Computer Weekly. He has an unlocked tri-band phone, which he puts a US sim card in. The calls internally are apparently very cheap, he can't recall exactly, but of course that may vary on tariff. Useful to phone each other, book cabs, restaurants etc. Suppose over time it would be worth storing favourite telephone numbers. His only reservation for other people is the cost of the sim card. If that is expensive then it may not be worth it for a one off holiday, but should be worth it if you intend visiting more often. Also, he said the cheapest way to phone UK is with a Calling card from AT&T. I shall look up details on this today and post.
So, who can find the cheapest US SIM card for us? Someone said they had seen them on e-bay. Further info please guys!!!