I personally use my w890i's ActiveSync synchronization to sync with Zimbra over the air and it works fine. The only limitation seems to be that the w890i doesn't support multiple calendars or contact lists -- it'll just sync the default Calendar and Contacts. Which is fine for my use case.
I don't ActiveSync e-mail, I pull it down OTA via the w890i's IMAP client.
I've been pretty happy with the capabilties of the w890i and Zimbra -- enough so that I haven't felt the need to get a BB or iPhone.
