You made my year, man! I saw your other post. We're glad you like it!
BlackBerry (RIM) has a lock on how BlackBerry works. All BB providers require a BES server, because that's what talks to their server in the cloud.
They own the cloud, and BBs never actually talk to any server. They will only talk to BB Headquaters. They've got a lock on that industry.
We do require BES or BES Express to work. Zimbra talks to that, and that talks to BES's cloud.
Hope that makes sense.