What are some alternatives?
Twilio - Brings voice and messaging to your web and mobile applications.
Plivo - Plivo's Voice API enables businesses to build Voice apps to reach customers globally in 200+ countries. Try Plivo's Voice API for free. Instant Sign Up.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
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.
KAPSYSTEM - KAP Computer Solutions Pvt. Ltd.,
Wassenger - Serverless WhatsApp API made simple