Twilio - Brings voice and messaging to your web and mobile applications.
Bulk SMS Services - Sending Bulk SMS to the customers will engage the customers with your business and new offers.
Plivo - Plivo simplifies your customer engagement.
Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.