Once an order has reached "preparing to ship" status, it can no longer be canceled, although customers still have 14 days to return the iPhone upon receiving it for a full refund. Once orders reached "shipped" status in the United States, they can usually be tracked on UPS's or FedEx's websites.
If your order has a Friday, September 20 delivery estimate, but has yet to reach "preparing to ship" status, this should change over the next few days. To check the status of your order, visit the Order Listing page on Apple's website.
The first deliveries to customers and in-store availability will begin Friday, September 20.
Discuss your iPhone pre-order in the MacRumors forums.