International direct dialing (IDD) or international subscriber dialing (ISD) is the process of an international telephone call

International call

International telephone calls are those made between different countries. These telephone calls are processed by international gateway exchanges . Charges for these calls were high initially but declined greatly during the 20th century due to advances in technology and liberalization. Originally...

 being placed by the caller (the subscriber) rather than by an operator

Telephone operator

A telephone operator is either* a person who provides assistance to a telephone caller, usually in the placing of operator assisted telephone calls such as calls from a pay phone, collect calls , calls which are billed to a credit card, station-to-station and person-to-person calls, and certain...

. The term international subscriber dialing was used in the United Kingdom and Australia until the terminology was changed to international direct dialing. Since the late 20th century, most international calls are dialed directly.

Calls are made by dialing the international call prefix for the country one is in, followed by the country calling code for the country one wishes to call, followed by the phone number within that country. When phone numbers are published for use abroad they typically include the country calling code, but replace the international call prefix with "+" to signify that the caller should use the prefix appropriate for their country. (For mobile phones, the plus sign (+) can be used instead of the prefix.

See also

• List of country calling codes
• List of international call prefixes
• Subscriber trunk dialing