gtalkx
Its still in the version 0.0.5. And its still not something that's very friendly.
What's good?
Its simple.
You can make voice calls. (was a hard thing just a few days back).
What's bad?
You can't log out unless you quit.
You can't change your status message or icon.
What's buggy?
Don't know whether its a bug or a super power - you can see invisible people. They are shown in the list of people who are online. Though you cannot make any contact with them. :)
Download the debian package from the link here: http://sites.google.com/site/jozsefbekes/Home/gtalx
Install it by running the following commands in command line.
sudo dpkg -i gtalx_0.0.5_i386.deb
or if you have 64-bit Ubuntu then
sudo dpkg -i gtalx_0.0.5_amd64.deb
Once it is done, run
sudo apt-get -f install
To remove gtalx just type
sudo apt-get remove gtalx