I have an IPhone that was purchased legally with the official local carrier in the Philippines and was given to me. I am currently residing in the USA... can my AT&T sim work with this IPhone? Or must something be done (e.g. jailbreak / unlock) for my IPhone to work in the USA? I tried placing my sim in the Iphone but it doesnt detect a signal. I don't know if its because the phone is locked, or if I have to register the IPhone with Itunes... Thanks in advance for any advice.