A few days ago I finally got it working. I now can synchronize my calendar and addressbook from my Android mobile (with synthesis syncml) to egroupware 1.8 and access this synchronized information via web interface or directly in Linux via GroupDAV with KDE’s Kontact/Akonadi (Kaddressbook, Kalendar) applications.
It was a stony path, though. Installing egroupware, activating its SyncML interface and allowing my egroupware user to use it went flawlessly apart from the fact that a new synchronizing account on my mobile (created with synthesis) had to be named (both parts of he account) after the mail address of the user registered in egroupware.
Accessing the synchronized data in eGroupware-1.8.001.20101201 with Kontact, turned out to be a real challenge , however. Despite several howtos for the 1.6 version in the internet I could not get it working with version 1.8. The authentication of Kontact at egroupware always failed with my hosted cgi based PHP solution.
After hours of debugging and looking through the code I found out that, the base64 encoding of the authentication information is not decoded correctly which is why authentication credentials cannot be extracted and thus egroupware authentication fails.