ya call them now and tell them your phone is falling apart and you would like to have your upgrade moved up, but you want to go into the store to buy the phone and dont mention you want the iphone 5. i just did this exact thing, although i had been complaing of a crappy phone for about 4 or 5 months now. but its worth a try.
Lol good luck with any of those crap tactics.. I think every carrier knows that customers will be calling with any and every excuse under the sun to get a new iPhone at new customer/renewal pricing..