I've got your frustration.
Thursday of pre-order week: Got up in the middle of the night to purchase new iPhone. I did it on a 2 year contract. Went back to bed.
Next day(Friday): I did the math and realized Att Next would save me $, so I panicked. I called both ATT and Apple, and they both said changing my order was doable without canceling, but no one who had the authority to edit or change ever said "yes". I wound up in an Apple store, speaking to the manager while his associate was on the phone to someone in Cupertino. End result: if I wanted to save the $, I needed to cancel and reorder, which I did.
Fast-forward to Launch Day. I stayed up late and noticed that one of the local Apple Stores showed stock of the phone I wanted, only problem was I had to cancel the pre-order I had to complete transaction (some of you now see where this is going). After I cancel, I go all the way through the pre-oder dialogue until I get to the grayed out "pick up in store". I was yet another victim of this clause Apple or ATT has put in their terms of service with one another.
So.... I figure "no problem." I get up early on Saturday morning, saunter down to the local Apple store and am greeted by a line longer than i've seen at even a release day for some iPhones. So I wait 2 hours. Finally, as I'm nearing the front of the line, someone appears from the Apple Store saying that they'd sold out of iPhone 6+'s.
That leaves me with a new online order and an end of October delivery date. I hope those are worst case scenarios as some have indicated that ship times are bumping up.