Country Code

The country code should be used when dialing TO that particular country FROM another country. In some cases you will also need to dial a city or area code. When a country name appears in the table as a link, there will be additional information regarding city or area codes. 

IDD Prefix (International Direct Dialing)

The IDD prefix is the access code needed to dial a call FROM the country listed TO another country. This is followed by the country code for the country you are calling (see above). The IDD situation in many countries has been changing regularly. Some countries have multiple IDDs, with each one used by a different long-distance carrier.

NDD Prefix (National Direct Dialing)

The NDD prefix is the access code used to make a call WITHIN that country from one city to another (when calling another city in the same vicinity, this may not be necessary).  The NDD is followed by the city/area code for the place you are calling (city/area codes, where applicable, can be viewed by following the link from the country name on the table below).   Phone numbers are often written in this format: +44-(0)1224-XXXX-XXXX.  This expresses the numbers used for both international and national long-distance calls.  In the example, +44 indicates the country code, while (0) indicates the NDD.  When dialing from outside the country, the NDD would not be used after dialing the country code; when dialing from within that country, the NDD would be used, but the country code would not.  

Looking up a number?

If you're trying to find the country of origin for an international phone number, you can look it up with the Fone Finder.

Sources: AT&T International Dialing Guide; Microsoft TechNet Knowledge Base; ITU Documents; Steve Kropla