ekiga on thin client

[one at one.cz]

Hello,
I would like to use SIP phone on edubuntu thin clients.
Sound in XMMS via eSound Output Plugin works fine. How to setup Ekiga or 
any SIP softphone to work on client? It starts but the sound is coming 
out from the speaker of the server. I tried to start ekiga 
--enable-sound --espeaker=10.0.0.20:16001 but nothing changed.

I will appreciate any help and experiences.
Oldrich