I followed AT&T instructions to unlock my iphone including the restore. Don't remember seeing a success message.
In the UK tried 2 SIM cards from T-mobile. Invalid SIM message on both.:smileysad:
On my return to the US, tried one of the UK SIM cards and it came up with iCloud activation request (e-mail and password) .. voila.. the UK SIM card connected to T-mobile US!
Tried the second UK SIM card. Worked without activation.
The Unlock does not activate on an Iphone, until you have inserted a new SIM card and got the activation message. I suspect this is Apple protecting your Iphone from being used after being stolen.
Hopefully the SIM cards will now work when I return to the UK!