Finally. The Enterprise Branch of KDE-Pim, the KDE Groupware Client, contains sources for the Scalix Connector for Kontact. Apart from Groupware support for e.g. Mail, Contacts and Calendaring, there is also an admin tool for the user, where he can adjust settings on the scalix server which Kontact itself does not support.
Here is the link to the Sources, get it via SVN:
svn co svn://anonsvn.kde.org/home/kde/branches/kdepim/enterprise/kdepim kdepim_enterprise
Great Job, folks, special thanks to Tobias Koenig!