ISD (International Subscriber Dialling) codes are, also called IDD (International Direct Dialling). These International calling codes defined by ITU ( International Telecommunication Union).
How to dial Other country telephone network ?
International Carrier Access Code (For ex, from India dial : 00 or + sign ) must be dialed before the country calling code, in order to select access to the international circuits of the network. Then Area code (if there), then the actual phone number to be dialed.
Dial Pattern :
[ISD_prefix] [ISDcode] [Area_code] [Phone_number]
- ISD prefix for International Carrier access, which is specific to the country from which the caller is dialing, but often it is 00 or 011 or prefix is specified with a plus sign (+). This prefix code is to be dialed before the country code.
- ISD Code (if applicable) - This is specific toa country. Some times same ISD code will be shared among the different countries.
- Area code & Phone Number - which are actual telephone you want to contact. This format will vary from county to country.