File:Phone pigpen.png

This is a variant of the pigpen cipher if it were invented by users of multi-tap text entry on a mobile phone.

Pigpen ciphers divide the alphabet into cells by drawing fence lines. Each glyph consists of the fence lines that border it, filled with dots or other marks to distinguish it from other letters in the same cell. For example, H in the left center cell is represented by a "right bracket" glyph (because it has fences on top, right, and bottom, but not left) and a dot. F in the top right cell is represented by an L-shaped glyph (with fences on left and bottom) and a stroke.

Different ciphers map glyphs to letters differently. For example, Rosicrucian pigpen writes the alphabet on three lines (A-I, J-R, S-Z), divides this into cells of three letters (ABC DEF GHI, then JKL etc.), and then indicates each letter by the surrounding fences and a dot in the left, center, or right of the cell. Freemason pigpen has a 9-cell pen for AN, BO, CP, DQ, .., IV, and then a separate 45-degree rotated 4-cell pen for JW KX LY MZ, with an empty cell for the first letter and a dot for the second.

Telephone pigpen arranges the letters as they appear on a telephone keypad. The letter-to-number assignment with 2 = ABC and 9 = WXY was used first by Telephone exchange names and later by phonewords and T9. The cipher leaves the cell empty for the first letter in a cell and adds a dot for the second or a stroke for the third.

Originally, Q and Z were not used in U.S. telephone exchange names and were thus not printed on keypads. This changed in the early 2000s, with Q placed between P and R on 7 and Z placed after Y on 9, as cell phones began to use them for text entry. The phone cipher leaves them out of the empty-dot-stroke sequence but adds them as a hook on the top of the letter.

Like other monoalphabetic substitution ciphers (see description page at File:Bill Meyer cipher.png), this could be used in fiction for a language of a minority among whom the ruling majority had suppressed literacy.

By Damian Yerrick, CC-Zero and probably ineligible for copyright anyway