I did and I was shocked, I was told they activation process was so slow, that you can just do it from your house, like the original iPhone, that was one PLUS from the slow servers today, being able to be the first one to open it and play with it.
I originaly bought a 16G black iPhone and the AT&T rep didnt open the phone when I walked out. This was the only reason I was able to return the 16G for the white one without incurring the restocking fee.
i actually walked out of the store with an unopened and activated iphone, so the crappy razr i had in my pocket was useless and i had no phone until i got home.
I opened mine at the store by choice and activated on iTunes right then, mostly because I just wanted to make sure it turned on ok, the screen looked good, and nothing odd happened.
All was well and I am busy playing around with it now!
They opened mine and activated at the spot, but they had me actually doing it, like taking out the phone and plugging it in the USB cable...I was okay with it since I wanted to make sure the LCD had no dead pixels before leaving anyway.