Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Sipdroid - Free and open-source SIP/VoIP Client
Sipnetic - Sipnetic is a free VoIP softphone based on the SIP protocol.
Fongo - free VoIP app - free Canadian phone number
Nertivia - Chat Client - Chat with friends or anyone around the world, free gif and emoji support.