idefisk : SIP and IAX/IAX2 software phone ( http://www.asteriskguru.com/idefisk/ )
linphone : Video softphone based on the SIP protocol ( http://www.linphone.org/ )
sflphone : SFLphone aims to become your desktop's VoIP companion. ( http://www.sflphone.org/ )
yate : YATE - Yet Another Telephony Engine ( http://yate.null.ro/ )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a voip
For Paludis use this rsync : rsync://gentoo.zugaina.org/voip-portage
If you have a problem : ycarus(-at-)zugaina.org