Where is MS's big play for business users in mobile phones?

While fewer and fewer, there are businesses that still deploy Black Berry phones. If it isn't, why is MS not making the biggest possible push to sweep up all the failing BB deployments? Most businesses in the world run MS software, could they not develop a level of integration with these that would allow businesses to quickly and easily deploy Windows Phone? Personally, I think they may have waited too long and because BYOD has managed to get a foothold, the opportunity may have slipped away. What do you think?