The Standard Ambiguous Code (SAC) defines the letters assigned to a specific numeric key on the mobile phone keypad. This assignment was standardized by the International Telecommunication Union
(ITU). For example, the SAC code assigns the letters A, B, C to the number key 2 on the mobile phone keypad, and the letters D, E, F, etc. to the number key 3. Most of the number keys are assigned three letters, only the number keys 7 and 9 are assigned four letters.