SMS is a worldwide technology used by almost everyone with a cell phone. Despite having a much greater reach than the smartphone market, SMS programming receives far less coverage and often remains uncapitalized. In this session, I will show you how to create a web site signup form that allows users to enter a mobile number. I will then show you how to use PHP for server-side phone number verification to check that the mobile number the user has entered is actually his mobile phone. Along the way, we will use jQuery to perform client-side validation and CodeIgniter as our development framework.