Report: Unlock WITHOUT Jailbreak on AT&T, just for travel!
I'm an AT&T customer and I unlocked my "Day 1" iPhone (upgraded to 1.1.4) with ziPhone. I chose "Advanced" and then "Unlock for any carrier". I left the original, activated AT&T SIM in while running the unlock. Piece of cake. No knowledge needed. No issues.
I didn't need Activation because I'm on AT&T and it's already activated. And I didn't want/need a Jailbreak, I'm happy to wait for the SDK and it's offspring. But I want to use my iPhone with foreign prepaid SIMcards when traveling, instead of paying exorbitant roaming rates to AT&T.
I can report that everything works flawlessly on my AT&T SIM as well as my foreign SIM (as well as my old T-Mobile US prepay). And I can change between SIMs without reactivating as long as I do it with the phone on. If the phone is turned off with a non-AT&T SIM, it needs to be reactivated when turning on again. I avoid this by always switching back to the AT&T SIM before powering off my phone and turning it on again. Only after it's back on I switch to another SIM.
Obviously Visual Voicemail only works on AT&T, but after a SIM switch, the phone first connects to Voicemail the way it does with other SIMs, by calling. After it connects you can hang up. You will then get a prompt for your password. Enter it and your Visual Voicemail is back.
I even reconnected to iTunes and did a complete restore and the phone remains unlocked!
Yes, Sbgi, I upgraded to 1.1.4 in iTunes before doing the unlock.
I am in Switzerland right now and noticed another thing: I turned the phone off with my Swiss SIM card in it and after turning it back on it did indeed ask me to reconnect to iTunes, but instead I just put the AT&T SIM back in and everything was fine. After that I switched back to the Swiss SIM and it worked again. So no fear about turning it off or running down the battery as long as you have your AT&T SIM with you.
BTW, AT&T's data roaming rates with the iPhone package plan are cheaper than anything available here, prepay or contract! I think that's pretty much the case all over Europe. I'm only here a week and Wi-Fi is widespread and I'm still using up my included 50MB for the month...