There is Scrybe which is supposed to have a lot of offline synchonisation which works well, so I hear.
Haven't had the chance to use it, as its a closed beta site now. Also dont know how well and how fast it renders on the Nokia IT's.

Google gears still doens tdo calendars and Google gears is in development for the IT (on garage project page)

Goovy is a flash based calendar,... again don't know much about it.