WikiPro - All-in-one Business to Customer Communication
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Heymarket - The professional way to text message. Your customers are mobile. Heymarket helps you manage those relationships from your smartphone.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Respond Flow - The Mailchimp of SMS
Plivo - Plivo simplifies your customer engagement.