Twilio - Brings voice and messaging to your web and mobile applications.
TelAPI - Build Apps With Our Cloud Based SMS & Voice API
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.
Tellephant - Helping you build incredible chatbots and integrate WhatsApp, Google, Facebook, SMS and more to your communication stack in seconds. All at the cheapest rates out there.
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.
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.