Hello,
I am currently using an SMS Gateway called Ozeki NG SMS Gateway to add SMS functionality for my Website. While I was searching found a page that describes how to add SMS functionality to Moodle: http://www.sms-integration.com/how-to-integrate-sms-functionality-into-moodle-193.html
I only meant to provide an advice and you might be interested in adding SMS functionality to Moodle.
BR,
Ryan