Just cancelled the preorder. Dialed 611 from my phone and then pressed 0. Short wait time, girl was very friendly and helpful. She said, "it says it can't be cancelled, but that's not right. Let me contact the right fulfillment center, they are the ones who cancel." She's even going to call me back within the hour to let me know that I am good to go with the upgrade eligibility refresh. She's just waiting on confirm from a different center. Now I get to go on a wild goose chase in NYC all weekend trying to find a phone, should be exciting, but wasn't going to wait until October 14th.
If the reps are denying you the cancellation and backorder column still shows 1, my advice is to dial 611, press 0, then be nice (ask how their day is going, weather, etc.), say you are confused (haven't gotten any e-mails since you placed order, want to make sure it's still in system, etc.). They'll tell you it's in there, won't ship until at least Oct. 5. If you get hesitation, I would suggest stating you are on vacation during those dates, and would rather try your luck at the at&t store in the area.