Bought AT&T black 16GB iPhone 5 as a walk-in purchase, via upgrade from my old 4, at Target 3 weeks ago today. Have buyer's remorse and want 32GB. No Target around here (Buffalo, NY area) has 32GB in stock. I can't reserve one via the Apple store pickup process because my line shows not eligible for upgrade, though I can add a 2nd line and reserve one that way. I don't want a 2nd line. Can I buy a 32GB as a 2nd line, port the phone# over, and then return the 16GB to Target within the 30-day window and be back where I want to be, with a 32GB single line with my current plan? Would I have to get a new line as the 2nd line with a new phone#, then swap SIMs with the old phone, and return/cancel the old phone attached to the new line, keeping the 32GB on the main number with the data plan I had purchased with the upgrade 3 weeks ago?