Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
3CX - Hosted PBX with CRM integration and mobile apps
Plivo - Plivo simplifies your customer engagement.