It is discovered that official Fedora OpenSync/libsyncml suite fails to synchronize Nokia N900 contacts/calendar. Although libsyncml-0.4.6 package is considered stable, it’s rather old and unable to handle N900 SyncML dialect properly. Newer versions of libsyncml (0.5.4) contains workaround, but Fedora is not likely to migrate to libsyncml-0.5.4 in near future as it breaks complete OpenSync infrastructure.
I’ve backported workaround from libsyncml-0.5.4 to current Fedora 14 version and submitted a patch to Fedora team. Hope it will be accepted once upon a time and we will see working version in Fedora repository. Until that happy moment you can download patched binary RPM package here.