Ekiga Softphone is mighty cool. On the surface it looks like just another update to GnomeMeeting, but it doesn't take long to realize it's oh so much more.
Here are some feature highlights (ripped from the site):
- Audio AND Video (SIP and H.323)
- STUN support (SIP and H.323)
- Echo Cancellation
I've tested it in Ubuntu 5.10 (Breezy Badger) and it worked fairly well*. If you're going to download it and try it, be sure to follow the build instructions listed on the site (under "How can I build?").
Lastly, I've heard through the grapevine that Ekiga works quite nicely with Diamondcard to let you call out to landlines...
*One minor quibble with the SIP stuff: I can't seem to get my microphone to capture input properly... When I do the recording and playback test, it plays back my mic input as choppy blips (even when doing the SIP echo test.) I haven't hunted around on the mailing lists, but I'm sure someone has a fix or something...