T9

In the T9 system, each digit key on the phone keypad corresponds to a set of letters. By pressing the keys multiple times, you cycle through the letters associated with each key. The mapping of letters to the keypad digits is based on the arrangement of letters on a standard telephone keypad:

To input a specific letter using the T9 method, you press the corresponding key multiple times until the desired letter appears. For example, pressing the "2" key once gives you the letter "A," pressing it twice gives you "B," and pressing it three times gives you "C." You cycle through the available letters on a particular key by repeatedly pressing it.

The T9 system was developed to simplify text input on devices with limited input capabilities, such as traditional numeric keypads. By using predictive algorithms, it guesses the desired word based on the sequence of key presses. The user can then select the desired word from a list of suggestions, speeding up the text input process.

It's worth noting that the T9 input method has become less common with the rise of touchscreen smartphones, which typically use virtual keyboards or swipe-based input methods. However, T9 was widely used on older mobile phones and had a significant impact on text messaging and mobile communication at the time.