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

AVOXI - AVOXI to deliver amazing call quality & an exceptional customer service experience.

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

Sonetel - Sonetel is a communication app that lets you make an international business call at the cost of local calls.

Plivo - Plivo simplifies your customer engagement.

Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs