I thought the same thing... and went yesterday to see if they did, even though online they said they didn't. At 10 when they opened they walked out and said they didn't have any phones.
So.. I'm just going to wait and see online when they get one. Since there was a ton of planes that landed yesterday I think theres a good chance stores will start to get even a few in. Reserving online gives you time to cancel your order and figure it all out vs walking in store then trying to cancel and not knowing how long it will take for the system to refresh so Apple can give you your discount.
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You can.. but.. I wouldn't do it until you have a phone in front of you, or know theres some at Apple so you can reserve it online then pick it up.
At this point.. I'm considering trying Walmart... Radioshack.. and all these other small places. Maybe they have one or two in and people aren't thinking about going ot these places. I know for midnight video game launches.. Gamestop has some 100-500+ people in line for major games and I literally just walk into walmart without a preorder and walk out at 12:05... maybe I can get lucky.