Phone company electronic switching systems use international country codes to route calls to their proper destinations. A phone number serves as a map for different switching offices. Phone companies may route calls through many different switching offices before creating a full circuit connection to the other end.
Phone numbers generally consists of an area code, which routes the call to a regional switching office, an exchange code, which routes to a local office, and the subscriber number for each specific customer. International calls require an extra procedure to route the call out of the country. Customers first enter an exit code, 011 in North America, which tells system that the call is leaving the system, and then customers enter the country code, which routes the call to the specific country desired.
Most country codes are two digits, such as Mexico: 52, and Germany: 49. The United States, Canada and several smaller countries share the country code: 1. Some smaller countries, such as Ireland, have three digit country codes. Many countries list a zero before the area code. Customers need to exclude this zero when calling from outside the country. For instance, to call the German number (044) 44XXXX from the United States, customers enter 011 49 44 44XXXX.