Here I am a new user, but in our company we uses open-Xchange for more then 2 years. There we use outlook with oxtender as client (and also the web interface).
Sometimes ago I installed OX on my home-server (debian etch), there we use in our family the web interface to coordinate our calendars. Between the years I found a little bit of time to make some test with Kontact (on AMD64-Kubuntu) but until yet I didn't find something how to connect Kontact to OX.
Where I have to search??
(best wishes for 2008 to all readers)