FrontlineSMS is a free software that turns a computer and a mobile phone or a modem into a two-way group messaging hub. Since it works at any place with mobile reception, it doesn’t need the Internet, which is a major advantage for many grassroots NGOs. Once the software is running on your computer, you can send messages to wide groups of people, and collect responses to any questions or surveys you might want to run, all via text message.

http://www.frontlinesms.com