Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Callmama - Get cheap international calling, international virtual number, Call Mama Gives an added advantage to send message and make calls to non-user of Callmama App.
XO Hosted PBX - Hosted PBX is a scalable UC solution that uses cloud technology to integrate HD voice & data services, mobility, along with advanced calling
CallHippo - Easy to use Phone System with World-Class Support
Sipdroid - Free and open-source SIP/VoIP Client
KrispCall - Virtual cloud phone system for business