hi there !
i've bought my new Iphone from a U.S. citizin and he shipped to me here in the uk.
he told me that the phone is fully unlocked.
but unfortunately when i got my phone, i couldn't make phone calls, the phone says "call failed!" even though the phone is perfectly able to send and receive text messages !
could u tell me what to do, or at least where to go to fix this problem ?

many thanks