This summer I’ve had the opportunity to experiment with a few H323 open source packages with a few colleagues. In general we had comparatively good luck with these tools. They connected great to my Tandberg MCU too! The only challenge was echo cancellation, but that probably could have been solved with a bit more effort and testing. Each of these worked great with a webcam.
So if you’re looking for a low-end solution, this might work for you! Please share any comments on your own experiments & testing with these tools.
June 16, 2009 Update: OpenPhone seems to no longer exist. Updated link to XMeeting.