Using early upgrades I have an iPhone 6 16 GB that I bought on launch day with a 2 year contract. I have an UDP, so I always buy with 2 year contracts.  I was thinking about selling my iPhone for $450 on craigslist and then using my early upgrade with AT&amp;T when the new iPhone comes out and get one with more storage.  I'd only end up paying like $100 to upgrade.  Are there any downsides to doing this? Is this something AT&amp;T would let me do every year?