WikiPro - All-in-one Business to Customer Communication
Amio Messaging SDK - Develop for multiple messengers using JavaScript
Heymarket - The professional way to text message. Your customers are mobile. Heymarket helps you manage those relationships from your smartphone.
Slack RTM API - Slack's Real Time Messaging API
Text Groove - Text enable your existing business landline, VoIP, or toll free phone number and connect with your customers in a whole new way. Try Text Groove for free.
Location SMS - Location SMS is an application that allows the users to locate themselves by sending a simple text ‘Where are you?’ to the phone.