International direct dialing
International direct dialing or international subscriber dialling is placing an international telephone call, dialed directly by a telephone subscriber, rather than by a telephone operator. Subscriber dialing of international calls typically requires an international call prefix to be dialed before the country code.
The term international subscriber dialling was used in the United Kingdom and Australia until the terminology was changed to international direct dialling. Since the late 20th century, most international calls are dialed directly.
Calls are initiated by dialing the international call prefix for the originating country, followed by the country calling code for the destination country, and finally the national telephone number of the destination. For example, a landline subscriber in the UK wishing to call Australia would first dial the following sequence: 00, followed by 61, followed by the national subscriber number.
International call prefix
An "international call prefix", "international dial-out code" or "international direct dial code" is a trunk prefix that indicates an international phone call. In the dialling sequence, the prefix precedes the country calling code.The international call prefix is defined in the telephone numbering plan of every country or telephone administration.
The International Telecommunication Union recommendation E.164 specifies the sequence 00 as a standard for the international call prefix and this has been implemented by the majority of countries. Member countries of the North American Numbering Plan use 011. Certain post-Soviet states continue to use 810 which was the universal IDD code across the Soviet Union. Other prefixes are also in use in a small number of countries.
Some countries require that the prefix 00 is followed immediately by the so-called carrier selection code, i.e., a numeric code that routes the call via a specific provider for international connectivity. Some countries may require that any carrier selection codes precede the international call prefix.
Some countries also offer simplified dialling arrangements for calls to neighbouring countries, usually by removing the need of dialling an international call prefix and the country code.
To avoid confusion especially in international context, a plus sign is often used as a graphic symbol of the international access code; it informs the caller to replace it with the prefix code appropriate for their country.