Are there any free applications for audio chatting via Google accounts in Ubuntu?

"Take a look at Empathy, it's a multi-protocol instant messaging app that, unlike Pidgin, does support Google Talk voice chat.

It's available in the Ubuntu repositories. You'll also need to install a backend for empathy in order to use gtalk. Install both with:

sudo apt-get install empathy telepathy-gabble"

Since version 2.6 Pidgin has audio and video support for gtalk. It's not in the ubuntu repos yet, but there should be debs somewhere.