Sprint Iphone work on straight talk?

I have a sprint iphone 5 however my sister is terminating her plan so i will to.
The question is that i see a sim card slot and was curious if i buy a sim card for straight talk will it work with the iphone from sprint?

- even though the contract with me wasnt 2 years must i return the phone or pay retail price?

Added (1). Since im not able to use my iphone for straight talk, im better off selling it and getting a cheaper phone fornow till i buy another for 650.00…

Whats the price of selling a locked, sprint, black 16 GB phone? D:

You do not have to return the phone to Sprint, but you must pay the Early termination Fee. Unfortunately, you would have to unlock the iPhone by Sprint for free, or a 3rd party company (for a fee), and even if it was unlocked, you won't be able to use it on a domestic GSM carrier, only an international GSM carrier. Apparently Sprint locks their iPhone 5 from use on domestic carriers &AT&T and T-Mobile and MVNOs like Straight Talk that use their towers).