Avochato - Text messaging for your business.
Twilio - Brings voice and messaging to your web and mobile applications.
Postscript - Like Mailchimp for SMS
Plivo - Plivo simplifies your customer engagement.
GetChat.App - Add WhatsApp chat to your website for free
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.