Apple store all the way.
But the question is: is it true, according to the Apple store employee, that we have to turn on the cellphone with non-AT&T microSIM for the first time, or it will be locked to AT&T for good/in the future???
And btw, the return period is just 14 days so I really need to make a call if I need to go through the trouble of exchanging iPhone and buying a T-mobile microSIM.
Thanks!!!
No, you do not need a non-AT&T microsim when you activate the 4S. Like I'd written, I'd accidentally left the AT&T microsim that was already in the 4S in when I'd activated it with iTunes. Then, I swapped my T-Mobile microsim in and it works fine.