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.