Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Nertivia - Chat Client - Chat with friends or anyone around the world, free gif and emoji support.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Sipdroid - Free and open-source SIP/VoIP Client