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
Zoom - Equip your team with tools designed to collaborate, connect, and engage with teammates and customers, no matter where you’re located, all in one platform.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Sipdroid - Free and open-source SIP/VoIP Client
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.