I'm not trolling when I ask, because I have zero experience with it, but what advantage does BES email have over a properly configured Exchange 2010 server?
Based on my understanding, most "properly configured" Exchange 2010 servers are inside of the corporate firewall sealed off. BES/BIS (whatever the name is) gives secured access to outside servers.
I think one of the salient features of Exchange 2010 is a Microsoft Sync technology that mimics some of the features of BES. Last I'd heard (I'm not in IT anymore, having instead chosen a career that actually matches my education), it was woefully worse than BES. Which is saying something.