I actually just got off the phone with AT&T myself and the representative stated a few things I thought might be valuable to this discussion:
(1) The "status" of your phone on the order page (ordered / backordered) does not mean anything. She said technically, all phones are on backorder since it's a preorder; however, there has been a glitch with the system in regards to how they were showing on the order status page.
(2) AT&T gets their shipment from Apple on the 17th, she recommended calling back in the evening on the 17th or the 18th to verify shipment date as she said reps will have more information - like whether the item is being packed for shipment, etc.
(3) From what she was told this afternoon, AT&T is close to it's expected shipment level which means those ordering from this point on most likely WON'T get them on the 19th.
Hope this helps!