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I would guess this is somewhere on your receipt...but just in case:

Returns
If you are not satisfied with your Apple purchase, return it with the original receipt and original packaging within fourteen (14) calendar days of the date of purchase. If the item is returned unopened, in the original box, we will exchange it or offer a refund based only on the original payment method. Apple will mail a check within ten (10) business days for cash, cash equivalent, and check transactions over $250. Except where prohibited, a 10% restocking fee will apply to any non-defective item that requires Apple to perform rework prior to resale; please ask a Mac Specialist for details. Please note the following:

Opened software, memory, and other media can be exchanged for the same item, but cannot be returned for a refund.
Custom-configured products, including any personalized iPod, cannot be returned or exchanged.
Purchases made using a lease are subject to the terms of your lease agreement and cannot be returned.
Non-Apple products are sold by Apple “as is.” Consult the manufacturer for warranty terms and conditions.
Products can be returned only in the country in which they were originally purchased.

That's for an Apple Retail Store. If you bought from an AT&T store...I'm sure they have their own policies.
 
Do they give you your cash back or do they pull the "We will mail you a check" crap?

Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.



Sorry....couldn't resist :D

Edit: Sorry, that should have been the answer to the question "What happens if you return an iPhone?"
 
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