Thanks for the response, adidaskid808 (Canada).
My smartphone is unlocked and 3G. It know it does work in the US as roaming works (but has been very expensive!).
Can you confirm that reverting from a smartphone package to the 10cents plan is allowed by AT&T. The 10cent plan is not available to smartphone users, so I am worried that once the Sim is registered as being in a smartphone then I will be prevented from going back.
I suppose I could put the sim back in my basic phone and ring from that, but it all seems a bit complicated.
I am on the THREE network in the UK and they have just introduced something called 'Feel At Home' which allows me to use my UK allowance (calls, texts and data) in the US with no roaming charges. Seems like an excellent deal other than the fact that calls to US numbers are not included - only calls home, although they are the main ones I make.
Thanks again,
Jonathan Harris