Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Clinked - White-label Client and Team Workspace
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Slack - A messaging app for teams who see through the Earth!
Sipdroid - Free and open-source SIP/VoIP Client
SuiteDash - Integrated & Automated Client Portal Software : Secure Web Based Client or Customer Login Portals : White Label SaaS Project Management System, Online CRM Tool, Browser Based Invoicing & Recurring Billing, Time Tracker, Client File Upload, , All in …