It seems that egroupware (a PHP based collaborative tool) is integrating horde syncML library, so that they can synchronize contacts, calendar, etc… with external sources (i.e. Exchange Server). The next 1.2. release will contain the source for that.
IDEA: It would be interesting to integrate ILIAS calendar with external servers.
Ah! my Siemens CX65 seems to be SyncML compatible 🙂
It seems to exist a commercial gateway to exchange servers, have a look.
Looking at this Exchange Server issue i finally found an open source solution that i didn’t know: Scalix, Enterprise email and calendaring for Linux.