To the OP: I wouldn't worry about it. My order says the same thing. If you look at it, it says, Item Status: Processing and then the Shipment Status: says Backorder as of today 10/7/11. That could just be langauge they put in their system representing things that are not shipping yet because they are not officially available. I don't think it actually means what it says. We're talking about AT&T and there have been a myriad of problems ordering with Unlimited Data Grandfathered and then having to accept a different Unlimited Data 4S package to people having CC problems.
All I can say is don't worry. I don't think that is the acutal real status of the order that is not going out yet.
Here is the bright side:
If it is actually backordered, you can always cancel the order, as they will not charge you by the time launch day is here because they aren't sending anything out and if you have an Apple store near you, or AT&T store, if you wanna go that way, you can pop into the store and buy the iPhone 4S on launch day or the day after or the day after that.
I know if this turns out to be true, all is not lost. I can and will cancel my order and take the trip to the city to get the phones.