My dad recently decided to get me a brand-new (opened package) GSM iPhone 4 16GB. What should I do with it?

Long story short, my dad's essentially trying to be a decent dad for once (I'm not even going to get into the details) and gave me his opened GSM iPhone 4 16GB. Its effectively brand-new and unused, but (almost) out of warranty. I'm on Sprint, and I can only stay on Sprint, no exceptions. So I have no idea what to do with it since I can't activate the phone on Sprint. I'm thinking about either using it as a high-end iPod touch, or selling it to buy my next smartphone. But I'm also interested in experimenting. So "Apple Core", what should I do with it?

EDIT: I already informed him about the incompatibilities of the different GSM/CDMA technologies.