A free (LGPL) PHP Script to send SMS easily to mobile phones worldwide and check their successful transmission from any Web site or computer application. Use the MCTEL SMSFAX Gateway (http://www.smsfax.com) for SMS transmission.
SMSec is a free , open source, GPLed implementation of two-factor authentication via SMS (Short Message Service). It uses SMSD to "talk" to GSM modems, provides a flexible XMLRPC web-service for web-developers integrate SMSec into their web-apps.