Sprint is the last major carrier over here to offer unlimited data that's not throttled at no extra charge. The other carriers have done away with it unless you pay extra or are grandfathered in from an old data plan. And on other carriers if you upgrade your device with a new 2yr contract and don't pay the full price for your phone, you lose your unlimited data unless you want to pay an extra $20 a month.
So with sprint it's all about unlimited data, cheaper devices and cheaper monthly bills. Basically, sprint users are a bunch of tight wads, including me.
Unfortunately sprint doesn't support windows phone very well. As of right now there isn't a single brand new windows phone out there for sale anywhere for sprint that I know of. None of the ones on the MS website will work on them because sprint is a cdma network. And the last windows phone they offered was the 635, or maybe the m8, I'm not sure. I just started checking windows phone out about a month ago.