RIM is still pretty strong in the enterprise market where, contrary to what some posters think, security is a BIG DEAL.
I wouldn't be suprised if Microsoft took a run at RIM. It would be a good fit given their focus on large corporate users. MS and BB might even add value to each other.
Apple doesn't seem to be directly interested in that market. Their penatration to date seems to be a carry over from the consumer market where they do quite well.