Have you tried gtalk with empathy? This way you shouldn't be running any non-free code at least on your own computer. If it works I think the best solution would be to start looking at how to build the server parts using free software.
No I've not but that's a good suggestion and that could well be the best free and open VoIP/VC solution if it works so I'll try that ASAP and report back here if I do so before the test-o-thon.
Thanks
Dan