I'm going to the UK in June and already have a jailbroken 3G, I didn't select "activate my iPhone" because I'm already on AT&T. When I'm over there, I can get a Pay-as-you-go SIM and can use it with any phone, in theory. Can I re-jailbreak, click "Activate my iPhone" and have it work with my AT&T SIM (ie does that option make the phone simply not care what network it's on?) until I go over there? Once over there, can I just pop the new SIM in and have the phone detect, search and such, or will I have to re-jailbreak with the new SIM already in there? Supposing both of the above is as easy as I'd like it to be, when I get back can I just shove my AT&T SIM back in, and be good to go?