So with Skype -- already proprietary software, already dubious -- probably going to Microsoft (as I read via Simon Phipps to the Grauniad and Johan Thelins) there's an extra impetus to find something else.

I'll just highlight Blink, a Python/Qt4 application for VoiP calls, video and chat (the latter I believe only on Mac and Windows right now, but the application runs on Linux, FreeBSD and I think I had it on OpenSolaris briefly, too) and SylkServer, a SIP server and conferencing solution.

Both are simple to set-up, are packaged for Debian, easy enough to get for other distro's and give you a complete, Free Software, SIP server and client infrastructure.

It's easy enough to escape from Skype to an open-standards-based world.