Twilio - Brings voice and messaging to your web and mobile applications.
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
SendSMSGate - ✅Send SMS Bulk and 📨📨📨 Service SMS and Viber ads all over the world. 💰Cheap rices, round-the-clock support and direct contracts with mobile operators.
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.