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ISD Full Form

What is the full form of ISD?

The ISD full form is International Subscriber Dialing. ISD, also known as IDD (International Direct Dialing), is a telephone call made directly by a telephone subscriber or an individual, as opposed to relying on a phone operator. Each country will be assigned an ISD number. This is a unique number or code.

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To make an international call, a telephone subscriber must include this code or number prior to the recipient’s phone number. Since the late 20th century, the majority of international calls have been made through direct dialing. When creating telephone numbers for international use, the international call prefix is disregarded and the number should begin with a plus sign (+) followed by the country’s call code. The + symbol indicates that a confirmation code may be required in the country where the call originated.


  • In 1957, Sally Reed in Dedham, Massachusetts made the first transatlantic direct dial telephone call to her penpal, Ann Morsley, in Dedham, Essex.
  • A country code is a component of the International Numbering Plan for Telephones. Dialing a telephone number to a foreign country requires the use of country codes.
  • The country code is prepended to the national telephone number. In contrast, international phone numbers contain a plus sign before the country code.

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