Recently, I use VoIP to call my family and some friends from Linux community. I use one of the easiest VoIP client available for Linux, Zoiper. Zoiper is available for Linux, Windows, Mac OS X, Android, and iOS. I will show you how to use Zoiper to make a call and receive a call in Ubuntu. I use voiprakyat as VoIP provider here. This tutorial can be applied in another distros too.