Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems

Mitel - Business Communications and Collaboration

Sipdroid - Free and open-source SIP/VoIP Client

Eir SIP Voice - eir SIP Voice is revolutionizing the core communications tool of business that carries both calls and data over just one connection.

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

Phonebooth - Phonebooth is one of the leading voip providers, providing phone systems & phone service for small businesses.