ISD Full Form

What is the full form of ISD?

The full form of ISD is International Subscriber Dialing. ISD is also known as an IDD (International Direct Dialing) is an international telephone call that is dialled directly by a telephone subscriber or an individual, rather than depending on the phone operator. Each nation shall be allotted an ISD number. .It is a specific number or code.

To make an international call, a telephone subscriber must add that particular code or number before the phone number of the individual. In the UK and Australia, the word ISD was used before the word was changed to IDD. Since the late 20th century most international calls are dialled directly. When telephone numbers are authored for international need, the international call prefix is ignored and the number should begin with a ‘ sign’ accompanied by the nation call code. The plus sign indicates it follows the country code and you might need to dial a confirmation code in the origin country.


  • In 1957 the first transatlantic direct dial telephone call was made to her penpal, Ann Morsley, in Dedham, Essex, by Sally Reed in Dedham, Massachusetts.
  • The International Numbering Plan for Telephones provides a country code as an item. Country codes are necessary if someone is dialling a telephone number to make a call to a foreign nation.
  • Nation codes are dialled before the National telephone number. By contract, the international phone numbers are constructed with ‘+ sign’ before the nation code.

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