Twilio - Brings voice and messaging to your web and mobile applications.
TelAPI - Build Apps With Our Cloud Based SMS & Voice API
Swift SMS Gateway - SMS Gateway is your bridge between the Internet and the world of cell phone SMS text messaging.
SMSAPI - SMSAPI.com is browser platform for bulk SMS and other SMS marketing solutions.
Maytapi - Serverless Whatsapp Api with Chat and Agent support.
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.