Twilio
Twilio is a provider of cloud communications platforms as a service. Twilio’s web service APIs allow software developers to make and receive phone calls, send and receive text messages, and perform other communication functions programmatically.
Plivo
Plivo is a cloud communication platform that allows businesses to modernize their business communications in a simple, fast, and scalable way. Plivo’s APIs and SDKs help companies of all sizes quickly integrate voice and SMS capabilities into their applications.
ICTCore
ICTCore allow developers to use multiple communication methods / services like Call, FAX, Messaging or Email, plus it also allow them to integrate these services with each other, like SMS notification after each call or email to fax.
Nexmo
Nexmo is a service that connects your applications to carriers all over the world. Using a single API, integrate SMS and voice messages. Register users, verify transactions, and implement two-factor authentication with Nexmo Validity.