I've been looking into this a little, and it really is a minefield. There's lots of so called standards and each piece of kit seems to impliment them in their own way.
Fortunaltly, Zimbra can export data in almost anything you want, and I did manage to export the calendar and import it into my regular mobile phone (Motorola V3x) just for testing. That phone supports ota sync but I couldnt get that working (must be a network edition feature) and I tried to connect to email via imap but struggled there too.
It really should be easier, and it's not really a zimbra fault that it's so tricky to get working, zimbra plays its part by being pretty open and using standard formats for it's exports so that's great. If I get my phone to work perfect with it then I'll see if I can register at the wiki and start an entire section giving specific instructions on a case by case basis (who's with me!?)
In the meantime though, some more info from the Zimbra team may be nice. It took me a while to understand that things like blackberry OTA sync is not supported on the OSS release, but there are work-arounds.
The short answer is try harder and experiment until you find something that works though.  | 
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