telephone number format Microsoft canonical address format for telephone numbers derives from E.123 international notation by allowing explicit indication of area code with parentheses. The canonical format is used by the Telephony API (TAPI), a Windows programming interface for dial-up fax, modem, and telephone equipment. Depending on the user's current location, the Windows' Dial-Up Networking (DUN) component applies a set of dialing rules to transform the canonical phone number into a locally dialable calling sequence for the modem device. The dialing rules may include variable-length dialing for area code, trunk access and international access prefixes, central office/service access numbers, and calling cards tone numbers. With this approach, phone numbers stored in the phone book remain unchanged when the user moves to a different geographical location or selects a different phone service provider. The calling sequence can contain dialable numbers such as digits 0–9 and DTMF tones ABCD*#, formatting characters ␣ . -, and control characters ! P T , W @ $ ? ;, which correspond to the Dial command of the Hayes AT command set. Emergency contact information A standardized language-independent way to identify a next-of-kin (or other emergency contact) in a mobile handset’s directory, in case of an emergency, has in May 2008 been adopted as a new clause in Recommendation E.123. It proposes to store emergency contact numbers prefixed with Arabic numerals in the form “0nxxxx”; “n” is a digit from 1 through 9 and “xxxx” is any meaningful descriptive character string in any language or script (e.g. “Anna” or “Spouse”). In the handset's directory this would be displayed as "01Anna" or "01Spouse" enabling easy identification by the emergency services. The handset’s directory entry (in the “contact number” field) would contain the actual number of the person to call in case of emergency. This scheme is a language-independent version of the "ICE" (In Case of Emergency) scheme that became popular in certain parts of the world from 2005 onwards. See also National conventions for writing telephone numbers E.164 List of country calling codes References External links International Telecommunication Union Recommendation E.123 Email Telephone numbers Network addressing ITU-T E Series Recommendations