Looks like AT&T and Apple can’t even take all the customers they want, with some customers reporting their pre-orders have been cancelled:
Your iPhone order has been cancelled. Your credit card has not been charged. If you believe you have received this email in error, please return to the AT&T store where you placed your order. Sincerely, AT&T
It’s probably a good idea to wait if you want the iPhone 4, especially with the number of things that have gone south including exposure of customer’s personal information during the pre-orders.