International Direct Dialing

International direct dialing (IDD) or international subscriber dialing (ISD) is the process of an international telephone call being placed by the caller (the subscriber) rather than by an operator. 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.