Get BlackBerry Enterprise Server Express for free!
BlackBery Enterprise Server Express wirelessly synchronizes Microsoft® Exchange or IBM® Lotus® Domino® with BlackBerry smartphones.
It provides advanced BlackBerry smartphone business features with no software license fees or additional per user license fees, and works with most personal BlackBerry data plans or BlackBerry enterprise data plans.
The BES is the only mobile device management tool out there and if you need to put mail on mobile devices along with other things like security or applications then this is the only clear choice. Apple and Google offer nothing like this (unfortunately).
Note: I think Nokia has a server that does some of these same things as the BES, but outside of Europe I don’ t think it’s used much? If anyone has any details you can post them in the comments.