Are there any updates to this? For my purposes we are using the NE edition of Zimbra (4.5.6) but anything which would allow bidirectional access to the calendars within Zimbra, without using Outlook, would be brilliant.
UPDATE: Well I believe that I "foot-mouthed" this one. After setting up
https://server/home/email_user_name/Calendar/ as an ICS calendar in ThunderBird/Lightning and creating a new event and making certain that it was set to the correct external Zimbra ICS calendar and not the builtin default one, it showed up in Zimbra as one would expect. That being said the same works from Kmail, although you have to also set the "Upload to" path, which is the same as the "Download From" one. I will play with this some more but it appears this is working.
Cheers,
RioGD