Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
D7SMS - Direct7 Networks provide highly reliable and cost effective Communication sms solutions to businesses across all industries.
Kannel - Open Source WAP and SMS Gateway
MyTask - MyTask is a centralized platform designed for office management, invoice management, and work management that allows a business to have the required service agility.
Ozeki NG SMS Gateway - Ozeki NG SMS Gateway is a powerful, reliable and flexible SMS Gateway application.
Group Texting - Group Texting provides your business with a robust Group texting software that supports up to 10-digits numbers.