Twilio - Brings voice and messaging to your web and mobile applications.
Kannel - Open Source WAP and SMS Gateway
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.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.
KAPSYSTEM - KAP Computer Solutions Pvt. Ltd.,