My university joined the AT43 project, which provides a VoIP infrastructure for Austria. In theory I am now reachable via my new telephonenumber sip:linneweh@at43.tuwien.ac.at or +43 (0) 59966-642055 from the normal telephone system.
I tested the two Softphone Applications that are available for FreeBSD. linphone is a GTK Application with a lot of Options, but an unusable GUI. kphone looks a bit oldfashioned, but the GUI is intuitive as it looks like an Instant Messanger and apart from some crashes it works.