Just a heads up: I got an email from AT&T this morning, telling me that my 4S order (that I stayed up until 3 am trying to place) couldn't go through, because they couldn't verify my credit card. Called AT&T and they said their system is having problems processing Visa cards and that several orders are being rejected. They tried to blame it on Visa, but who knows. They were unable to change my credit card to a non Visa card and I was told that all they can do is resubmit the order and hope that somehow, it goes through this time. If not, I go to the back of the line with everyone else who attempts to get a phone when it's released. They claim they just found out about the error this morning and that's why they didn't put any mention of the problem on their site, so people could use a different card.
Regardless, just thought I'd make folks aware about this, if they don't know already. Don't use a Visa card when ordering your phone.
Incidentally, I tried to send a tip to TIPB about this so they could warn people, but their contact page works about as well as AT&T's ordering system. So please, spread the word. Don't use Visa if you want your phone. At least if you want it sometime before 2012.