Reaching out to the targeted audience, is one of the goal for any business. here is a list of modules which will allow your website to interact with your audience
Other then the module mentioned above you will need an active subscription to a SMS Gateway to send or recieve SMS and a module which can integrate these gateways, Drupal modules for the following SMS Gateways are available
To Test the service you can even use Email Gateways or Log Only Mode availaable in SMS Framework. A complete list of Supported Gateways is available here.