I too would like to figure this out. If there was a way to sync Google calendars with Zimbra bidirectionally, I would be able to use my Gmail account as a hub to most of my mail and calendaring for both home and work without having to sync my iphone to my work systems.
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Culley
Mail | Dell 2950III | 2x Quad Core 5420 | 8gb RAM | 6x 146gb SAS RAID 0+1 | Red Hat 5.3 | Zimbra 6.0.10 Network Edition
Test | VMware ESXi Whitebox | Phenom II Black 3.2ghz | 12gb RAM | 6x 1tb SATA RAID 0+1 | CentOS 5.4 | FOSS, Not in use now |