I'm also in the same boat, currently using OSS but soon switching to NE. Anyways I have setup a funambol server and dabbled in the admin a bit, I also setup a test account on
http://my.funambol.com so you can test things like the Blackberry Client, Outlook and Thunderbird.
BTW the Thunderbird + Lighting + Funambol extension has been updated to support Lightning 0.5.
Get it here:
SourceForge.net: Funambol Mozilla Plugin
Also try using ScheduleWorld for testing as they keep update with blackberry's and Thunderbird.
I have successfully synced Thunderbird Contacts to my.funambol.com, working on Calendars as it seems to find them, and the entries, but doesn't upload them, but I wonder if that's because they are remote calendars.
BTW the reason to use a test funambol account is because 1) it was free, and 2) Once you get it working both ways, you should only have to change the server the plugins/add-ons/clients point to.
The next step which I think is already done it syncing directly from Zimbra to Funambol Server to Client/PDA/ipod/BB/WM5. Check the forums for posts by Doud, he said he got it to work, but we'll have to wait for a solid tutorial/how-to.