Every country structures their long codes slightly differently. In the US, 10-digit long codes include a three-digit area code, followed by a three-digit exchange, followed by four more digits. The final seven digits are called the subscriber number.
In India, by contrast, long codes for landlines start with a two- to eight-digit subscriber trunk dialing (STD) code. The number following the STD is a one-digit operator code that indicates which telecom provider is responsible for the number. The rest of the digits are the subscriber number. Mobile long codes start with a four-digit operator code, followed by the subscriber number. Long codes in India are always 10 digits long.
Global phone numbers follow the E.164 standard, which limits long codes to no more than 15 numbers, including country code. In practice, no country takes the full 15. Most countries’ long codes are eight to 11 digits in length. Italy and China have the longest long codes, with 13 digits, while Niue, with a population of fewer than 2,000, has four-digit long codes.