There is some discussion in this thread about this issue but the thread itself starts off with a different question so anyone simply reading through might miss it, so I figured I would start another thread for this issue specifically. It seems that I am one of at least three people who are experiencing this issue. When configuring caldav on the iPhone, one of two things happens depending on the account method used.
I should mention that my email address has a different domain than the zimbra server domain; so the zimbra is at zimbra.domain1.com and my email address associated with that zimbra account is firstname.lastname@example.org - I don't know if this is important or not, but I wanted to just mention it. So below, your.zimbraserver.com is not the same domain as the email address doman, "domain.com".
With full email address (method 1):
User Name: email@example.com
Use SSL: Yes
Account URL: https://your.zimbraserver.com/princi...firstname.lastname@example.org
-- I should note that after entering the above into the box, it changed it to read: https://your.zimbraserver.com:443/pr...%40domain.com/
Without full email address (method 2):
User Name: firstname.lastname
Use SSL: Yes
Account URL: https://your.zimbraserver.com/princi...tname.lastname
With method 1, the calendar shows up in the calendar listing, but all entries that were there before span through the year 2145, and show up as taking up the entire day from now through to the year 2145. They also show as having grayed out and dashed line borders in the calendar view.
With method 2, the account verification is successful, where presumably it checks the server to make sure the login is good. After going through all the settings, however, I go to view my calendar and the Zimbra calendar that I just set up in "Settings" doesn't even show in the list of available calendars.