Twilio - Brings voice and messaging to your web and mobile applications.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Plivo - Plivo simplifies your customer engagement.
TeleSign - TeleSign offers end-to-end communications Platform as a Service.
smooch - Smooch connects your business software to all the world’s messaging channels for a more human customer experience.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates