Here's what it says after you placed your pre-order:

"Your order has been completed.

Your order number is xxxxxxxxxx. Pre-orders for iPhone 4 and iPhone 3GS 8 GB will be processed to arrive as early as June 24, 2010, if submitted by June 22, 2010. The actual shipment date and receipt of your order is not guaranteed and may be subject to delays for reasons that include, but are not limited to product availability, inventory, credit issues, number porting or carrier delays, and completion of other required AT&T businsess processes.

Additional items added to the cart at the time of your pre-order may ship separately depending on availability.

All pre-orders taken online are being handled on a first-come, first-served basis."

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Notice it said Pre-orders arrive as early as June 24 if submitted by June 22. That's not possible as the iPhone 4 is now sold out and AT&T has stated further pre-orders would not be received by customers until "June 25 or later."
Apple.com pre-orders are now shipping by July 2nd.