RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Asterisk - An open source telephony switching and private branch exchange service for Linux.
CallHippo - Easy to use Phone System with World-Class Support
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.
Cloud Telephony - Cloud Telephony delivers automated telephone applications to any phone, any place, anytime.
Kamailio - Kamailio® (successor of former OpenSER and SER) is an open source SIP server released under...