Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Kannel - Open Source WAP and SMS Gateway
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Power SMPP - Enterprise grade messaging software
KAPSYSTEM - KAP Computer Solutions Pvt. Ltd.,
Moxtra - Moxtra is a multi layered, embeddable team collaboration solution.