Twilio - Brings voice and messaging to your web and mobile applications.
46elks - Adding SMS and voice to your application or service should be easy.
Maytapi - Serverless Whatsapp Api with Chat and Agent support.
freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).
Swift SMS Gateway - SMS Gateway is your bridge between the Internet and the world of cell phone SMS text messaging.
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.