The country code as defined by the ITU. This extension is used when a system wishes to designate specific parts of a phone number (and potentially place constraints on which components must be present and how they're filled in).

The area/zone/city code that, in some areas, may be omitted when dialing locally within the zone. This extension is used when a system wishes to designate specific parts of a phone number (and potentially place constraints on which components must be present and how they're filled in).

The local number that must be dialed to connect within the area/city/zone. This extension is used when a system wishes to designate specific parts of a phone number (and potentially place constraints on which components must be present and how they're filled in).

The number that may be dialed within a private phone network or after successfully connecting to a private phone network. This extension is used when a system wishes to designate specific parts of a phone number (and potentially place constraints on which components must be present and how they're filled in).