I'm not sure what all the differences are between freeswitch and asterisk but once you're on the horse It's easier to keep riding it than switching to another one. Twinkle seems more stable than linphonec. In conferences they have what's called energy level which seems to mean you are muted unless your audio level is above a certain value. This seems to reduce echo problems. Both twinkle and linphone hade mute/unmute commands and you could always define a key with loadkeys. To get to a conference go to 3000 at linux-speakup.org, you shouldn't have to put in the port 5830 any more. Also works with sjphone which is a windows sip client.