Twilio - Brings voice and messaging to your web and mobile applications.

Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...

Plivo - Plivo simplifies your customer engagement.

Discord - Step up your game with a modern voice & text chat app. Crystal clear voice, multiple server and channel support, mobile apps, and more.

Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates

Vivox - Vivox is called to be one of the leading chatting platforms for online gamers.