FrontlineSMS is a free, open source software that allows for instantaneous two-way communication via SMS text messaging.

FrontlineSMS is unique in that it does not require an Internet connection to function. Essentially, FrontlineSMS works by allowing users to connect an array of mobile devices to a computer. In doing so, FrontlineSMS effectively turns any computer and mobile phone, or modem, into a two-way communication hub from which SMS text messages can be sent and received.

FrontlineSMS attests that its software can be used to send SMS text messages to large groups of people anywhere there is a mobile signal.

http://www.frontlinesms.com/

http://en.wikipedia.org/wiki/FrontlineSMS