Atomic SMS Sender - Free bulk SMS software to send bulk text messages from PC
Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Twilio - Brings voice and messaging to your web and mobile applications.
Kannel - Open Source WAP and SMS Gateway
ExpressText.net - SMS marketing that helps to increase sales and generate more repeat business. Get your message in Infront of customers with just a few clicks.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.