Twilio - Brings voice and messaging to your web and mobile applications.
Callmama - Get cheap international calling, international virtual number, Call Mama Gives an added advantage to send message and make calls to non-user of Callmama App.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
CallHippo - Easy to use Phone System with World-Class Support
KrispCall - Virtual cloud phone system for business
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs