Hm, I take that back. Looks like the linux version is unavailable and being ported - as you said. The site I was looking at, was actually openwengo, - much better than the zoep site. My bad.

The Wengo Firefox Extension has indeed already been released for Win32, and builds for both Mac OS X and GNU/Linux will be available shortly.

A recent .DEB package of the classic "desktop" WengoPhone and full source code is available from the recently redesigned OpenWengo developer website. The crew hangs out on freenode #openwengo - come and say hi ;)