I am due for an upgrade and what I really want is an iPhone... but AT&T doesn't give equipment discounts on iPhones (boo!) So I wanted to buy a discounted phone from amazon.com with a contract extension, sell it and use it to help subsidize my iPhone purchase. Amazon.com says you can't transfer the device to another line of service (lest they charge you $250) but really, how can they keep track? Has anyone done this?