Sprint is still looking to capitalize on its investment in the iPhone, and it looks like its found a way to lure iPhone users to the service. Beginning tomorrow, Sprint will give you at least $100 towards a new iPhone 4S when you trade in any iPhone model when you agree to Sprint two-year contract. The promotion will run through the end of June.

Sprint is currently the only iPhone carrier that offers unlimited data for new customers. Is that enough to make you consider making a switch?