RemoteCalendar is a CalDAV client for iPhone and iPod touch and works with DAViCal from 0.96.
Product page: remote-calendar.com
To connect to your DAViCal account, load RemoteCalendar from iTunes and create a new CalDAV account in RemoteCalendar. Type in the URL to your CalDAV home and your credentials and it should work. If not, please contact the support: support (at) remote-calendar (dot) com.
RemoteCalendar is really superseded by the release of the iPhone OS 3.x which does support CalDAV in the standard calendar application.