Sprint: iPhone 4S to iPhone 5?

I've been under Sprint for about 3 months now with an iPhone 4S. I've been wondering if I can trade in this phone for an iPhone 5 under the same contract. Is this at all possible? Will I have to pay extra?

Yes, you can do it. They have dials all the time with the iphone5 so you can trade with no extra cost. But if they don't than you will have to pay the difference for the device