Telephone users can use webpages such as AT&T's International Dialing Guide to double check telephone country codes. They can also use country code tables to look up codes alphabetically.
AT&T's webpage allows users to select the country they are calling from and the country they want to call. It then pulls up precise instructions on how to use the correct country code.
When calling international telephone numbers from North America, users must always dial "011" before entering the country code. However, they do not need to dial this prefix when calling long distance numbers within the United States or Canada. Country codes can have anywhere between one and three digits.