Originally Posted by Quentin

Sure thing -- it's a very simple process.

When the user enters their number via the online form, they are taken to a page that says "Enter the code you received to confirm your subscription."

They then receive an SMS message to the number they entered, which says: "Type in this word:" and there's a confirmation code that follows the colon. They enter that code in the form on the confirmation page, and their SMS subscription is confirmed.

Pretty straightforward.