I'm currently traveling overseas and just received ATT's approval email to unlock my iPhone 6. I don't have a local sim nor did I bring my laptop (no iTunes). Is there a timeframe which I need to perform the unlock procedure after the approval? I expect to return to the States in 4 weeks and hope it will not be too late. I presume once ATT sends request to Apple to unlock it should stay unlock at Apple database forever, right? Thanks!