Twilio - Brings voice and messaging to your web and mobile applications.
Maytapi - Serverless Whatsapp Api with Chat and Agent support.
Plivo - Plivo simplifies your customer engagement.
Swift SMS Gateway - SMS Gateway is your bridge between the Internet and the world of cell phone SMS text messaging.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Tellephant - Helping you build incredible chatbots and integrate WhatsApp, Google, Facebook, SMS and more to your communication stack in seconds. All at the cheapest rates out there.