Phone Keypad Cipher

Phone keypad codes are the methods for writing text using the keys on a phone keypad (numbered 0 to 9, sometimes with * and #).

There are mainly 2 modes for entering text in the absence of a full keyboard:

— the ABC or Multi-tap mode on the one hand, which allows you to write a character by repeating a key

— the T9 mode on the other hand, which uses a dictionary to obtain intuitive input and avoid repeating keys.

On the same old model of mobile phone, these modes can coexist but are incompatible.

By default, on a mobile keypad (smartphone, iphone), letters are associated to digits according to this arrangement:

T9 has short numbers, whose length (number of digits) is equal to the number of letters in the word.

There is little repetition of the same digit.

The digit 1 is rarely used.

The input is minimal and fast (only 1 press per key) for each letter and encourages typing SMS without abbreviations.

The ABC multitap has long numbers (often much longer than the original word)

There are many repetitions of consecutive numbers (corresponding to successive presses of the same key).

The number 1 is rarely used.

This is the historical and tedious method that led to the use of many abbreviations in writing SMS.

Vanity is a technique of personalizing phone numbers by using letters associated with numbers to form memorable words or phrases (sometimes called Phonewords).

Vanity code is the name given by the Anglo-Saxons to the codes above. Some give it for the T9 mode, others for the ABC/Multitap mode.