Something else to consider...
Tmobile also just started offer unlimited data. So now Sprint can't advertise that they are the only ones.
All carriers need their nitch. But we all know they can/will make up certain claims to make themselves look better (largest network, fastest network, etc). What will Sprint's marketing claim be to show that they are better then everyone else? It seems some peple are still thinking they are cheaper then Tmobile. I think they are close but they only get that way by offering a restrictive voice plan.
I think increasing prices would really hurt Sprint. Problem is... can they survive their LTE roll out without it. TM can only do it thanks to the AT&T spectrum and AT&T's billions paid in the failed "merger".
IMHO Sprint is hanging on right now for 2 reasons... they have the iPhone and they have limited expenses so far in their LTE roll out.