A simple example: Your web site requires a user to register some personal details in order to receive a password for access to your web content. You're keen to know the users mobile number. You simply have the user fill out a form on your site, but the password is sent automatically via SMS text to the users mobile phone. Only users that have entered a valid mobile number will have received the password.

This is achieved by including a HTTP request to your providers server, in your web form. Your provider's server receives the request and automatically sends the SMS text containing a unique password.