Avochato - Text messaging for your business.
WikiPro - All-in-one Business to Customer Communication
Postscript - Like Mailchimp for SMS
Respond Flow - The Mailchimp of SMS
GetChat.App - Add WhatsApp chat to your website for free
Proximiti MessagePro - MessagePro services include business SMS, secure messaging, interactive messaging, BOTs, scheduled messaging, and fax. Solutions for SMB and enterprise.