Ian, you can just drop into a Walmart and buy a Track-Phone. I've never used them, but the terrorists love them
Seriously, you pay about $50 for one, and it includes phone minutes. When you're finished with it, you just throw it away.
http://www.tracfone.com/index.jsp Thanks - does that give me a regular US cell number?
Essentially I am going to divert my office phones to it - as it will be a lot cheaper than taking my calls on a Uk mobile phone - I would have to pay around $2+ a minute to accept incoming calls - hence the need for a US cell phone.
I can bring an unlocked phone, so even a sim will do.
However my fear is that the phone company may require a US address.