Instructions
Press the "Start" button on your controller to bring up the game menu.
Press the left or right trigger to cycle through the menu options until you reach the phone.
Scroll down to "Dial" using the left analog stick on your controller. Press the "A" button to select the "Dial" option.
Navigate to the number that corresponds to the letter you want to type. This number and letter association is the same as it is on any touchtone phone and each set of letters is listed right next to the number. Press "A" to make your selection.
Scroll to "Call" and press "A" to complete the code.