Other things going wrong that I can't find in open tickets:
The application crashed after I closed preferences. The window remained open but nothing worked, I had to kill java manually. After that the application never started anymore, now I can only do it by sudo sip-communicator.
I tried a call between two clients and the receiving one answered: 488 not accpetable (the typo is real too) instead of 200 OK.
NEC Europe Ltd.
NEC Laboratories Europe
Network Research Division