A key assignment method assigns large sets of alphabetic and other characters and functions to the keys of a standard numeric keypad for text/data entry on an electronic device. Two letters are assigned in pairs to each key of the standard 12-key keypad in a first character mode, and other symbols, characters, or infrequently used letters are assigned in a second or more optional character modes. A mode selection key is provided to select between the modes. In the first character mode, a keypress of a key selects the first letter of the pair and two keypresses in succession selects the second letter. The letter pairs may be assigned in alphabetic order, except for infrequently used letters, such as `Q` and `Z`, or in QWERTY order, or in pairs of a more frequently-used letter with a less frequently-used letter. By comparison to the standard phone keypad layout having an average KPD=2.2, this method can achieve a KPD=1.4 or lower. The standard directional arrow keys (RDI keys) may be used for mode selection in multiple character modes. Using the RDI mode selector can transform the conventional 12-key telephone keypad into the equivalent of a 60-key data entry layout (or expandable by 48 more keys for each additional mode keystroke used), thereby allowing operation comparable to a full QWERTY keyboard of characters, with enhanced symbols and functions, and/or with multi-language character sets.