This is a great question, I do not have an exact answer on this yet but I did find some information that may help. I will do some more digging on this and post what I find out here. This is from a FAQ that we have on the iPhone:
Are Sprint exclusive applications like Sprint Navigation, and NASCAR Sprint Cup Mobile available on iPhone?
This is giving me iPhone pre-order remorse. Sprint's GPS Navigation app is superior to iPhone's Tom Tom and Garmin apps as it locks on your exact location better and does voice turn-by-turn directions, including street names, traffic alerts (without additional charge), and distance. On my road trip to Vegas, my girlfriend used Garmin on her iPhone (Verizon) -- we ended up using Sprint's GPS Navigation app on my Pre due to its frustrating execution. I really hope you can download the app somehow.
I did a quick search in the app store and found the free version of Telenav. It's...ok-ish but no voice command or rerouting. The paid-for version, which is called "Navigation By Telenav" is even more feature rich than the one Sprint was offering and right now, only 99 cents. I think there is a $9 yearly fee but, honestly, it's not that bad considering the Magellen and Tom-Tom apps are around $50 a piece.