Are there any instant messengers for Ubuntu that support video and audio chat?
Skype also supports video and voice chat on Linux.
Or you could use Ekiga (VoIP client) for video and voice.
Gyachi has this on their web page:
This Yahoo! client for Linux operating system supports almost all of the features you would expect to find on the official Windows Yahoo! client: Voice chat, webcams, faders, 'nicknames', audibles, avatars, display images, and more. Yet, it remains very light-weight and memory-friendly.memory-friendly.
Meebo is a web service that supports voice and video chats on Linux.