"Smart" phones and CalDAV or iCalendar over WebDAV

I'm trying to set up access to shared calendars for a few users at my
company. I've got a CalDAV server (http://rscds.sourceforge.net/) and a
WebDAV server setup - from Thunderbird, users can access calendars
stored on either of these, and even those that insist on using Outlook
can use WebDAV.

However, I can't find any way to get anyone's so-called "smart" phone to
access the remote calendars. There a couple of different types I'd like
to get working - one runs Symbian, the others have WinCE. Neither seem
to have any way of accessing or synchronising to a remote camera. Does
anyone have any ideas, pointers or suggestions here? Failing that, are
there any phone/pda devices available which actually do a decent job?
I'm trying to find something *reliable* that supports IMAP for email,
calendar sharing (preferably CalDAV, but iCalendar over WebDAV will do),
WLAN, and 3G, and which doesn't require expensive proprietary server
software.

mvh.,

David