Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Way2SMS - Way2SMS.com is an online portal based in Hyderabad, India, offering free and unlimited SMS across...
Kannel - Open Source WAP and SMS Gateway
Textfree - Send text/SMS messages from your PC from a free phone number
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Targlets.com - A kind SMS platform. Bulk SMS, Marketing and API.