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.
Mitel - Business Communications and Collaboration
HoduPBX - Communication with your team streamlined. Simple & easy!
Phonebooth - Phonebooth is one of the leading voip providers, providing phone systems & phone service for small businesses.
CounterPath Softphone Client Suite - CounterPath enables users to make VoIP audio and video calls, send instant messages and manage their presence in an easy-to-use software.