Gtalk client that works on Linux, it supports voice and text based chat. It is not packaged for any particular distro, but if you are lucky enough, running a script will get it built. We test and use it on KUbuntu, Zenwalk and Slackware. Some people reported that it works on Fedora, Mandriva and Debian as well.
If you need help installing it, take a look at the contact us paragraph on the homepage. You can also find deb files there for Ubuntu.
Good luck! :-)