Sip-communicator promises to be easier, better, and more open than the competition. I’ve only just installed it but it looks like a winner.
Add this PPA:
deb http://download.sip-communicator.org/deb unstable/
Then go to a terminal and type the following commands:-
apt-get install sip-communicator-keyring
apt-get install sip-communicator
Then go into Applications -> Internet -> SIP Communicator
THANKS: John Lewis