How Country Calling Codes Work
The international number format
An international phone number is written as a plus sign, the country calling code, and the national significant number. For example, +44 20 7946 0958 starts with the United Kingdom's +44, followed by the London area code 20 and the local number.
The plus sign represents the international access prefix used in the caller's country, which can be 00, 011, or another sequence. Storing or writing the number with a plus sign keeps it valid in any country.
How ITU-T assigns the code space
The International Telecommunication Union's Telecommunication Standardization Sector manages the E.164 numbering plan. Codes are grouped by world zone: for example, zone 1 is North America, zone 4 is Europe, and zone 8 is East Asia and some Pacific destinations.
Most countries receive a short code such as +33 or +81, while smaller or later-assigned destinations may use longer codes such as +234 for Nigeria or +856 for Laos.
What to check before dialing
Confirm the destination's calling code in this lookup, then verify whether the local number already includes a trunk prefix such as 0. National trunk prefixes are usually dropped after the country code when dialing internationally.
Shared-code destinations need extra care. Dialing +1 from outside North America connects to the North American numbering plan, but you still need the three-digit area code, such as 212 for New York, 416 for Toronto, or 876 for Jamaica.