As far as I know there is no official "unlocked" phone from AT&T. Yes you can buy an unlocked iPhone overseas and yes, you can use third party services and jailbreak programs to open up an iPhone but I don't believe you can take your AT&T activated phone to Europe and replace the SIM card with a card from another carrier
Unlocked iPhones
As far as I know there is no official "unlocked" phone from AT&T. Yes you can buy an unlocked iPhone overseas and yes, you can use third party services and jailbreak programs to open up an iPhone but I don't believe you can take your AT&T activated phone to Europe and replace the SIM card with a card from another carrier