My son is moving overseas indefinitely, with 3-4 one-week-long US visits a year, and he wants to keep his long-time US number and have the use of the phone on his trips back here without the running expense of keeping a monthly account going....while he's using the phone overseas with a different SIM card and number. QUESTION: Can he transfer his existing number to a pay-as-you go account on any other carrier and then park the SIM card until he lands in the US again and then plug and play? ATT is behaving erratically and has told him "yes, we can do that...but not with an iPhone???" Other carriers are telling him the accounts are only good for 90 days. Any tips to solve this issue? Thanks.