There is NO reason why Apple can not activate the phones in the Apple store right when you buy the phone.
I get phones activated and deactivated all the time. I control about 50 cell phones for the salespeople in my company. These guys are losing phones, losing sim chips (how?), or just plain breaking them all them time. I am constantly swapping numbers, getting new lines activated, turning old phones off, etc...
Granted I am not a cell store employee and this is all done through T-Mobile not Cingular/AT&T but this isn't rocket science. It can all be done remotely, over the air. I call up T-Mobile, explain the problem, and they zap whatever it is they need to zap, tell me to power cycle the phone and all is good with the world. The only time I have to actually go the T-Mobile store is when I need a new SIM card.
I am sure that Apple/AT&T has made the whole process as simple and as streamlined as possible. At least they better have. I suspect it will all be done via a special website that Apple employees willl have access to. AT&T employees will probably just follow whatever normal procedures they do for every other phone.
The only reason I can see for going to an AT&T store over an Apple store is if you have some weird plan issue that you think might be out of the ordinary, something AT&T employees may be familiar with while Apple sotre employees may not. Or if the AT&T store is an easier place to camp at. ;-)
- SR