If you were one of the early adopters who purchased your iPhone between June 29, 2007 and August 21, 2007 then you are now eligible for $100 Apple Store Credit.
Details on how to pick up this store credit can be found here. The process seems straight-forward enough:
Step 1: Identify your iPhone To confirm eligibility, simply enter your phone number and iPhone serial number in the fields provided.
Step 2: Enter your access code You will receive an SMS text message on your iPhone containing the access code to redeem your $100 credit. Enter your phone number and your access code in the fields provided to generate an electronic store credit.
Step 3: Get your $100 Apple Store credit You will receive a $100 electronic store credit to purchase products at the Apple Retail Store or the Apple Online Store.
Here's the small print:
Requests for the $100 credit must be submitted by November 30, 2007. You must activate your iPhone with AT&T prior to submitting your claim. Once you activate, return to this page after 24 hours to request your credit.
You can view the FAQ relating to the store credit here. A few noteworthy points include: