Not wanting to repeat the sad story of hacking some misbegotten file somewhere inside iSync that will get replaced when Apple finally gets around to adding a couple more lines of XML code to a .plist (and testing it all properly, of course), I decided to learn once and for all how to create iSync plugins, and picked up Feisar's V600i plugin to figure out what was necessary.
20 minutes later (including a quick incursion through Fireworks), it was working:
...and you can get the plugin here.
In case you skip that bit in the README -
SUPPORT: There is none. I will not reply to any queries regarding how to get this to work with your Communicator, since it is mostly a matter of luck (and there is, after all, only a limited number of ways this can be done wrong - it either works or it doesn't). Ditto for data problems of any sort.
That said, contact syncing works fine for me so far (contact pictures, multiple numbers/addresses, notes, etc.). I haven't tried (and won't try) iCal syncing, since I sync the 9300's calendar with my Exchange server and don't want to mess with it.
The 9500 we tried it on, however, blew up spectacularly (well, ok, it crashed), even though the phone IDs were apparently correct. My guess is that you need to have a 5.x series firmware for SyncML to work properly (some would say "at all", but hey, that's another issue).