Apple has posted a rebate-how-to for early iPhone buyers (before August 22.) It's an easy process that results in an instant electronic Apple Store credit. Incidentally, you do not need a store receipt, all you need is an active iPhone and an internet connection.
NOTE #1: If you look closely at the graphics on Apple's Refund page, you'll notice the pictured iPhone is running firmware version 1.1.1 -- The current iPhone firmware is 1.0.2, so it's safe to assume an update is imminent. You might also notice that there is a new setting for the 'Home Button.' We assume this new setting will allow users to access playback controls just like the iPod Touch. (We hope it will allow the Home button to be customized -- for our money, we'd be tickled pink if you could push the home button twice to instantly bring up the phone application.