Finally right below the mobile phone field in Preferences choose your notification option. To receive text messages you must choose the TXT Message option in the My preference for receiving library notices pull down menu.
Please remember that text messages may not be free for you depending on your mobile plan, and the library will not be held responsible for any cost you may incur. This is a feature you have to opt into. Many patrons already receive email notices on their phones; the texting option is just another choice that is available to you.