Telephone keypad in the context of DTMF

An input method (or input method editor, commonly abbreviated IME) is an operating system component or program that enables users to generate characters not natively available on their input devices by using sequences of characters (or mouse operations) that are available to them. Using an input method is usually necessary for languages that have more graphemes than there are keys on the keyboard.

For instance, on the computer, this allows the user of Latin keyboards to input Chinese, Japanese, Korean and Indic characters. On hand-held devices, it enables the user to type on the numeric keypad to enter Latin alphabet characters (or any other alphabet characters) or touch a screen display to input text. On some operating systems, an input method is also used to define the behavior of the dead keys.

Phonewords are mnemonic phrases represented as alphanumeric equivalents of a telephone number. In many countries, the digits on the telephone keypad also have letters assigned. By replacing the digits of a telephone number with the corresponding letters, it is sometimes possible to form a whole or partial word, an acronym, abbreviation, or some other alphanumeric combination.

Phonewords are the most common vanity numbers, although a few all-numeric vanity phone numbers are used. Toll-free telephone numbers are often branded using phonewords; some firms use easily memorable vanity telephone numbers like 1-800 Contacts, 1-800-Flowers, 1-866-RING-RING, or 1-800-GOT-JUNK? as brands for flagship products or names for entire companies.

E.161 is an ITU-T Recommendation that defines the arrangement of digits, letters, and symbols on telephone keypads and rotary dials. It also defines the recommended mapping between the basic Latin alphabet and digits (e.g., "DEF" on 3). Uses for this mapping include:

• Multi-tap and predictive text systems.
• Forming phonewords from telephone numbers.
• Using alphabetic characters (e.g. as a mnemonic) in a personal identification number.

Keypads are specified both in the common 4 × 3 and several variations, such as 6 × 2 and 2 × 5. E.161 also specifies the dimensions and characteristics of the star and square, referred to in the standard as the 'star' and 'square' keys, respectively. (In practice, the 'square' key is almost invariably replaced by the number sign. and the sextile symbol is the more common choice for the star key.)