Twilio - Brings voice and messaging to your web and mobile applications.
Tropo - Tropo is a cloud API for voice and messaging.
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Skebby - Skebby is a leading and best SMS messaging solution providing platform that allows you to send thousands of messages to your customers around the globe.