Yes, it's an actual sync, though not a very sophisticated one (can't deal with multiple changes on a single item without data loss). You can sync to a remote FS using something an SSH pipe, for example, and do anything to the remote file from there to get the info into your groupware app.
The groupware of choice for KDE seems to be kolab, but it's a massive package, it's quite buggy, and when Matt Douhan implemented PDA for one project, he used TS'ed outlooks and Activesync with Windows Mobile PDA's
The major problem the Z's have is that they have no permanent over-the-air capability without getting dirty (CF cards stickingout, etc).
Maybe you can try with a 6000 (the only one with built-in 802.11) but you'd need to trigger the sync from the device because the radio will gun down your battery in just over an hour.
Also, KdePim/PI is not integrated with the distro's connection managers, so you'll have to turn it on manually or write a script.
Good luck trying to sync with all 3 platforms, let us know if you achieve anything interesting.