Sprint-Nextel was mentioned along with AT&T and Verizon as the carriers businesses work with most. That means T-Mobile is out and the Android isn't getting any serious love from the business community.
I am always amazed at the Blackberry penetration. The devices themselves fail to impress me and Blackberry has shown itself to be unreliable compared to companies that run Exchange. All email communications run through RIM's servers at some point in the world and at least once or twice a year, we seem to hear of a regional outage affecting a continent or two. This cannot happen with Microsoft's solution. If your Exchange server goes down, then you are stuck, but no one else in the world is. Having RIM between your corporate servers and your phone is just one more link in a chain that can fail. On top of it all, it is an extra cost. Many IT departments already have Exchange which synchronizes with a number of platforms. Buying Blackberry Enterprise Server is an extra expense, and another link in the chain that can fail.
Yet IT departments flock to RIM's solution. It goes to show what a solid solution for messaging RIM has, and that is what IT departments focus on. They aren't terribly interested in media, web browsing and other goodies that Windows Mobile and other platforms seem to handle better.
We'll have to see if Windows Mobile 6.5 offers anything that would cause more enterprises to adopt a Windows Mobile device. Most of the features I've seen versus 6.1 are consumer oriented, answering the iPhone challenge on some fronts. Apple has already provided Exchange ActiveSync support, but until they get real serious about security and remote administration, the iPhone will continue to be a consumer-only device.