AVOXI - AVOXI to deliver amazing call quality & an exceptional customer service experience.
Asterisk - An open source telephony switching and private branch exchange service for Linux.
SIP3.IO TAPIR - VoIP troubleshooting, customer experience, and network performance management
Wazo.io - The UCaaS Platform Built for MSPs
Global Call Forwarding - Global Call Forwarding offers local and international toll free numbers which can be forwarded to any phone, anywhere in the world.
FreeSWITCH - FreeSWITCH is an open-source media application designed to support popular protools such as SIP and WebRTC and provides a platform to develop voice and video applications.