I'm pretty disappointed too. But this is the first hiccup I've had regarding a preorder with AT&T.
I Blame Apple more than anything. They seem to be, even though they finally manufactured them, in denial that anyone would actually want a 5.5" iPhone. They seemed to think it was a fringe product.
6s are said to be in plentiful supply.
I blame Apple too.... if they did not have enough stock to cover the first 15 minutes of pre-orders, how can Tim Cook stand on stage and announce the 6 Plus goes on pre-order 9/12?