Scenario: You have been waiting in line for three days. You are one of the first with an iPhone. You get it home, walk through the easy iTunes setup and... VOILA! You are rejected for AT&T service because your credit sucks. This is not a joke, it very well could happen. So AT&T is offering in-store credit checks, for the less-than-confident. Apple Stores, however, will not check your credit in-store, so be wary.
In the words of AT&T:
The credit approval for your AT&T service also happens on your computer. It's part of activating through iTunes, but if you'd rather have your credit pre-approved before you leave the store, an AT&T store representative can help you with that.
Some more fine print:
iPhone is covered by the Apple Warranty. There is no eligibility for the wireless phone insurance program.
Available only to consumer accounts. iPhone and associated wireless service are not eligible for corporate discounts.
You can return your iPhone within 14 days for a full refund, but there is a 10% restocking fee if the box has been opened.
Download the full AT&T PDF here.