The crown jewel of Sprint's service is undeniably its "truly" unlimited data, so when rumors of the Sprint iPhone started surfacing, customers of the Now Network immediately started questioning what would happen to data plans as a result.
The other two carriers currently offering the iPhone, Verizon and AT&T, both switched to tiered data plans shortly after they started carrying the device, so it was an understandable fear coming from Sprintsters across the nation that they, too, may end up on the same [horrible] system. Fortunately, though, "people familiar with the matter" have told Bloomberg otherwise -- Sprint will indeed be keeping its current unlimited data packages around after the launch of the iPhone, with no plans of switching to tiered data plans.
Keep in mind, though, the Sprint iPhone is still just a rumor in itself, so all statements associated with the device should be taken with a grain of salt until we hear official work from Mr. Hesse himself.