Twilio - Brings voice and messaging to your web and mobile applications.
Phonexia Voicebot Suite - Phonexia Voicebot Suite is an all-in-one voicebot-building solution for the rapid, on-premise development of highly sophisticated conversational AI interfaces for contact centers and other automated systems.
Plivo - Plivo simplifies your customer engagement.
monosay - Intelligent Bot Platform
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Dialogflow - Conversational UX Platform. (ex API.ai)