Twilio - Brings voice and messaging to your web and mobile applications.
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.
MirrorFly - World's Most Scalable Voice, Video & Chat SDK for Small, Medium & Enterprises
Plivo - Plivo simplifies your customer engagement.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates