Blackberry Enterprise Server Express & OCS
While this probably meets the needs of most places (up to 2000 Blackberry email users) if you take a look at the comparison chart you’ll find this freebie version does not support instant messaging for OCS. Bummer.
What that comparison chart doesn’t say is that it only supports OCS 2007. RIM has decided not make their client OCS 2007 R2 compatible.