Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
CSipSimple - CSipSimple is a SIP application for android devices.
VoIP.ms - VoIP.ms is a VoIP origination and termination tool.
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
Mitel - Business Communications and Collaboration
HoduPBX - Communication with your team streamlined. Simple & easy!