My father has an upgrade he is never going to use with AT&T. He has offered to let me use it to get my girlfriend an iPhone 5 since her Verizon contract won't let her upgrade for almost another year. The only problem is that my father's line does not have a data plan. Obviously buying an iPhone on it will add one. Is it possible to use the upgrade, get the iPhone, pass it off, put my dad's old dumbphone back on the line, and cancel the data plan?