Which keypad layout does this use?

It uses the standard ITU-T E.161 layout found on mobile phones: 2 holds ABC, 3 holds DEF, 4 GHI, 5 JKL, 6 MNO, 7 PQRS, 8 TUV, and 9 WXYZ. Keys 7 and 9 have four letters each.

How are press counts shown?

A letter is written as its digit repeated once per tap. A is 2, B is 22, C is 222, and S is 7777. This multi-tap notation is unambiguous because the repetition count identifies the exact letter.

What happens to spaces and digits?

On real phones a space is the 0 key, so spaces are shown as 0. Digits 0 to 9 are passed through as themselves, and any other character such as punctuation is left unchanged.

How is this different from ambiguous T9?

Ambiguous T9 writes only the digit once per letter, so 2 could mean A, B, or C and software guesses the word. This multi-tap version repeats the digit by tap count, so each letter is uniquely recoverable without a dictionary.

Is letter case preserved?

No. Phone keypads have no case, so all letters are treated case-insensitively and mapped to the same key sequence whether they were typed in uppercase or lowercase.

Telephone Keypad T9 Encoder

The telephone keypad encoder turns text into the multi-tap key presses people used to type SMS messages on a numeric phone keypad. Each letter is one of three or four characters sharing a key, so you tap that key the right number of times: A is one tap of 2, B is two taps, C is three taps.

How it works

The encoder uses the ITU-T E.161 keypad layout and writes each letter as its key digit repeated by the tap position of that letter on the key:

2 ABC   3 DEF   4 GHI   5 JKL   6 MNO   7 PQRS   8 TUV   9 WXYZ   0 space
A=2  B=22  C=222
S=7  position 4 -> 7777

Letters from one word are separated by spaces in the output so the boundaries between presses are clear; a space character maps to the 0 key.

Example and notes

HI encodes to 44 444 — H is the second letter on key 4 (44) and I is the third (444). The repetition count makes multi-tap unambiguous, which is the key difference from predictive T9: you never need a dictionary to read it back. On a real handset you would pause between two letters on the same key, and that pause is what the space in the output represents.