MessageBird Voice API - Add programmatic call capabilities to your app or service
Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
MessageBird Chat API - Connect with your customers through different messaging apps
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Voiceflow - Build voice apps in your browser without coding
Kannel - Open Source WAP and SMS Gateway