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What is the full form of ISD?

Full form of ISD: Here, we are going to learn about the ISD, full form of ISD, overview, history, examples, types etc.
Submitted by Anushree Goswami, on November 28, 2019

ISD: International Subscriber Dialing

ISD is an abbreviation of International Subscriber Dialing. It is also called as "International Direct Dialing (IDD)". This term stated as an International telephone call made by a person without depending on the telephone operator. The terminology of the term international subscriber dialing was changed to international direct dialing till it was used in the United Kingdom and Australia in the late 20th century. To every country, ISD is allocated. To make an international call, a subscriber has to attach this code before the specified person's phone number. ISD is a specific number.


For the emerging countries, calls are begun by dialing the international call prefix, accompanied by the country calling code for the destination country, and in the last the national telephone number of the destination.

For international use, when phone numbers are prepared and issued, the international call prefix is excluded and the number should begin with a plus sign (+) accompanied by the country calling code. The plus sign specifies that the country code follows and that in the emerging country, access code may have to be dialed.

In 1957, by Sally Reed in Dedham, Massachusetts the first transatlantic direct dial telephone call was made to her penpal, Ann Morsley, in Dedham, Essex.

The international telephone numbering plan comprises a country code as an element. Country codes are essential when there is someone dialing a telephone number to set up a call to another country.

Before the national telephone number, country codes are dialed. By agreement, international telephone numbers are constituted by prefixing the country code with a plus sign (+), which also specifies that the local international call prefix should first be dialed to the subscriber.

For example,

The international call prefix in all countries belonging to the North American Numbering Plan is 011.

In most European, Asian and African countries, it is 00.

On GSM cellular networks, when the user prefixes a dialed number with the plus sign, the prefix may automatically be inserted.

For placing an international call, an international call prefix or dial out code is a trunk prefix. It is used to choose an international telephone circuit. It is now these days known as an IDD prefix (international direct dialing).

Other Full Forms of ISD are,

  1. ISD: International Society of Dermatology
  2. ISD: Indiana School for the Deaf

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