The Apple Store will accept returns for those who couldn't cancel their online orders. I'm sure someone would be waiting to buy that one at the store.You should be able to decipher your shipper with the tracking number received. UPS usually starts with 1Z while USPS usually starts with 92 or 94. Not sure about FedEx or other couriers.
Your local AT&T store should accept a return as long as you have your receipt.