avaamo - Simple, Secure Business Messaging
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Facebook Messenger - Facebook Messenger is a faster way to message.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Plivo - Plivo simplifies your customer engagement.