CounterPath’s X-Lite is the market’s leading free SIP based softphone available for download.
Combining voice and video calls, Instant Messaging and presence management in an intuitive and familiar interface, X-Lite helps you seamlessly transition from a traditional hard phone environment into the world of Voice over IP.
To learn how to install X-Lite on your system please watch this video.
One of the best things about Nimbuzz is that it is easy to install and has a very user friendly interface. With Nimbuzz you can add all your contacts from different Communities such as: Facebook, Myspace, Yahoo Messenger, etc.
You can easily add any VoIP provider in Nimbuzz from those they already have in their list or add your own VoIP provider which you are most used to.
In order to learn how to install and add a VoIP provider in Nimbuzz watch this video or watch this for advaced settings.