Avochato - Text messaging for your business.
SMSGlobal - SMSGlobal offers a web-based platform and API's enabling businesses to send mass SMS's.
Postscript - Like Mailchimp for SMS
Tatango - Tatango is a mobile messaging platform for agencies.
GetChat.App - Add WhatsApp chat to your website for free
WikiPro - All-in-one Business to Customer Communication