LinuxTent

Empathy is a new instant messaging client in Gnome 2.24 which aim to replace pidgin and Ekiga. It provide voice and video chat services besides the usual text chatting service.

To Install Empathy you first have to add the hardy repository:
sudo bash -c 'echo deb http://ppa.launchpad.net/telepathy/ubuntu hardy main >> /etc/apt/sources.list'
For Interpid Ibex:
sudo bash -c 'echo deb http://ppa.launchpad.net/telepathy/ubuntu intrepid main >> /etc/apt/sources.list'
For Gutsy Gibbon:
sudo bash -c 'echo deb http://ppa.launchpad.net/telepathy/ubuntu gutsy main >> /etc/apt/sources.list'

Then you have to update your packages lists, so execute:
sudo apt-get update

Now you are ready to install Empathy:
sudo apt-get install empathy telepathy-mission-control telepathy-stream-engine

Enjoy calling

To install google talk support:
sudo apt-get install telepathy-gabble
To install MSN support:
sudo apt-get install telepathy-butterfly
To install Pidgin support, this will allow you to use all the protocols supported by libpurble [pidgin backend]. This will help you to add Yahoo :
sudo apt-get install telepathy-haze
To Install IRC support:
sudo apt-get install telepathy-idle
To Install all supported protocols in one shot, you can install :
sudo apt-get install telepathy-core