The 12-button alphanumeric telephone keypad is a prime example. The letters on each key–“ABC” on the 2 key, “DEF” on the 3 key, and so on–are a legacy of the 1920s, when phone numbers ...

Each number key (2-9) on a T9 keypad is mapped to a set of letters. For example, the key "2" corresponds to "ABC," "3" to "DEF," and so on. Android phones have had the feature for years ...