Sure you can. You just use the proceeds of the sale to pay off the device. I believe payoff at the 12 month mark for any capacity iPhone 5s on Jump is $324 ($27.50x12). As long as you make more than that from the sale, you're ahead.Except you don't get to actually sell the phone and get that money from the sale (unless you actually paid off the whole price of the phone). That's the whole catch behind it all.