Country Calling Code (CCC) or ISD

What is Country Calling Code (CCC) or ISD?

✍: FYIcenter.com

Country Calling Code (CCC), also referred as ISD (International Subscriber Dialing) Code, is a 1 to 3 digits number that enables International Direct Dialing (IDD) into a country or region identified by this number.

Note that the Country Calling Code of your phone number is only useful to your international friends who want to call you.

For example, you live in New York have a land phone line with a local number of "123-4567" and an area code of "212". Your phone service provider supports phone calls at 3 levels:

Local Calls - Your friends in New York have phone numbers in the same area code of "212". They dial your local number, 1234567, directly to reach your phone.
National (Long Distance) Calls - Your friends in Las Vegas have phone numbers in area code of "702". They must dial your area code followed by your local number, 212-1234567 to reach your phone.
International Calls - Your friends in India or France have phone numbers not in the North America Region. You must give them your number as "1 (212) 123-4567", where "1" is the Country Calling Code (CCC) for US.

So, you really have 3 phones numbers for 3 different types of phone call services:

Local Number: 123-4567 - For Local Call service within the same area code. By the way, the type of services are not used any more, because mobile phone networks do not respect area codes well.
National Number: (212) 123-4567 - For National Call service within the same Country Calling Code.
International Number: 1 (212) 123-4567 - For International Call service world wide.

Technically, your international friends can not dial your International Number, 1 (212) 123-4567, directly to reach you, because their phones are programmed by default to make National Calls within their country or region only. They must dial first the International Dialing Code (IDC) of their country or region to override the default.

For example, your friends in India must dial to 00-1-2121234567 to reach your phone, where since the International Dialing Code (IDC) for India is "00".

As you can see, making an International Call is not easy. People must remember and dial 3 chunks of numbers:

International Dialing Code (IDC) - This is to inform the phone network that the caller want to dial out of the country or region where the caller is from. This is really the International Dial-Out Code. For example, "00" is the International Dialing Code for India and some other countries.
Country Calling Code (CCC) - This is to inform the phone network that the caller wants to dial in to the country or region where the receiver is located. This is really the International Dial-In Code. For example, "1" is the Country Calling Code for US and some other North America countries.
National Number - This is the phone number (including the area code) of the receiver. For example, (212) 123-4567 is your National Number.

Here is a diagram that shows you how the Country Calling Code (CCC) is used in the dialing sequence of someone calling from India to US.

                  International Dialing Code
                  |
                  |    Country Calling Code
                  |   ------------------- 
                  |   |
                  |   |   Area code
                  |   |   |   Local number
                  v   v   v   v
Dialing Sequence: 00  1   202 1234567
Dialing Sequence:  +  1   202 1234567

Please note that most of today's smart phones allows to use "+" as a shorthand dialing key to represent the International Dialing Code, regardless from which country or region you are dialing out. This is why you can print your US phone number in 2 formats: