Maemo5 does not support SyncML out of the box. SyncML is a standard used to synchronize clients with a SyncML server. There are open source server software (like Funambol provides) and a lot of clients for nearly every plattform as you can see here. The idea is to have also a solution to synchronize Contacts, calendar entries, tasks and notes (and maybe more stuff) from the N900 (Maemo5) to a SyncML server.
Services (free and paid) offering SyncML can be found here.
Thread in talk.maemo.org to discuss: http://talk.maemo.org/showthread.php?t=37034