Give them a little while. They are the last national carrier to begin carrying the BBs. They've had their own product for years "business connect" which they've always insisted was better (it was a joke). And then sided with GoodLink. I'd question their support for the BBs. TMO sells more BBs than any other carrier in the country so their relationship with RIM should be stronger.
Sprint may end up being a decent BB provider in the long run, but they just finally launched the 7750 (I know...old) and the 7250. Let them figure out the bugs first before jumping with them. They've purposely tried to avoide the BB platform so let them embrace it fully first. I have several contacts at Sprint and most people at Sprint just do not get the concept of push email.
Current - 8700g TMO
Previous - 7280 AWS, 7730 TMO, 7290 TMO
Long ago - 950 model (still have it)