From the overview page:
FrontlineSMS is a desktop software created to lower barriers to positive social change using mobile technology. By leveraging basic tools already available to most organizations, including those in ‘last-mile’ settings — computers and low-cost modems — FrontlineSMS enables instantaneous two-way communication to any mobile handset. It’s easy to implement, simple to operate, and best of all, the software is free; you only pay for the messages you send. Using FrontlineSMS with FrontlineSync, you can also track missed calls for the first time.
Our award-winning open-source software has been downloaded over 100,000 times since its first prototype in 2005, and helps organizations all over the world overcome communications barriers. What you communicate is up to you.