Twilio - Brings voice and messaging to your web and mobile applications.
Plivo - Plivo simplifies your customer engagement.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Applozic - Chat API & In-App Messaging SDK for Mobile & Web Apps Innovate fast, save development cost and delight users with a scalable, secure and customizable Chat
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
CALLR - CALLR is an extremely helpful app for those who have to deal with call control protocols for their business. You can create a customized call control system that will perform a wide range of functions.