A:AnswerNo, you shouldn't need a new contract unless you're planning to lease the phone, in which case you're locked in for the term length. We don't have a "contract" with Sprint, we can leave any time (and we would if any of the other major carriers could come close to the service price) but we did take advantage of their promotion for $150 (split over 24 months) off if you purchase the phone and finance (through Best Buy).
The promotions change so you'd need to go in or call Best Buy to find out what they or Sprint is running.
A:AnswerYou can find out who much you will probably get by going to the Best Buy website. You can also bring it with the charger to a Best Buy store be sure to set it back to factory setting before trading it in.