FWIW...
I pre-ordered two iPhone 6 128 GB phones and online, they both show as "Preparing to Ship" but one is 9/17/14-9/18/14 and the other is 9/23/14-10/02/14.
I have spoken to and chatted with a few different ATT reps who all say that both devices should arrive on 9/19.
The automated number on the order status page (877.782.8870) tells me the first order has been processed and the second is backordered.
However, when I spoke to a rep, she gave me another number to try - 866.391.0749 and it tells me that both orders have been sent to the warehouse for shipment, which agrees with what the reps have been telling me.
Anyway, the second number seems to have more info than the first, at least in my case.
Hope that helps. Now, back to the waiting...
Have you tried signing up for UPS MyChoice? See my post from the last page, took me 5 minutes and I got to see my tracking # and delivery date of 9/19. It's the only way I could get tracking info, my AT&T status shows the same as yours...ship date of 9/17-9/18 delivery on 9/19. I was a little concerned seeing some people reporting getting 'bumped' out of their 9/19 date, but with the UPS utility, you get a tracking # and it verifies your delivery date if there's a concern. Just an option