iPhone Return Policy
If you are not fully satisfied with your iPhone purchase, you can return your undamaged iPhone to the Apple Online Store within 30 days of purchase for a full refund. Please visit online Order Status or call 1-800-676-2775 to request a return. If you return your iPhone within 30 calendar days from shipment, you will not be charged a restocking fee. The iPhone must be returned in the original packaging, including any accessories, manuals, and documentation.
http://store.apple.com/Catalog/US/Images/salespolicies.html#iphonereturns
I'd call them. I returned mine to apple.com last week and they put the reason as 'changed mind' instead of what I really reported with the proximity sensor issue. I haven't received my refund yet.