Area Code 231 – Oslo
The phone area code for Oslo is 231 (international format +47231). Browse local exchange codes (NXX) and carrier assignments below.
📞 Exchange Codes (NXX) for Area Code 231
Select a central office code to view local carrier data and detailed information
📍 Geographic Location of Oslo
Geographic Coverage and Administrative Context
The +47 231 prefix is a geographic National Destination Code (NDC) assigned to the central administrative area of Oslo, Norway. As part of the Norwegian numbering plan administered by the Norwegian Communications Authority (Nkom), this code routes calls to fixed-line subscribers within a defined exchange area of the capital. Oslo is the country's political, economic, and cultural hub, and the 231 numbering block serves both residential and business customers in the city's core districts, including the governmental quarter and surrounding commercial zones. Unlike mobile prefixes, 231 is tied to physical locations, meaning that the number's geographic association remains with Oslo even if the subscriber moves to another part of the country, unless number portability applies.
Dialing Formats and Caller Instructions
For international callers, the full E.164 format is essential: dial the international access prefix (e.g., 00 from most European countries, or + from mobile networks), followed by Norway's country code 47, and then the subscriber number, which includes the 231 prefix. For example, a local Oslo number might be dialed as +47 231 XX XXX from abroad. Within Norway, callers must dial the complete eight-digit subscriber number, including the leading '2', as Norway uses closed numbering plan without trunk prefix '0'. Thus, a domestic call to the same number would be 231 XX XXX. It is important to note that the geographic prefix does not require an area code in the traditional sense; the entire number is dialed uniformly across the country.
Overlays and Numbering Considerations
Oslo has multiple geographic NDCs, including 21, 22, 23, 24, and others, which are not overlays but separate numbering blocks that share the same geographic area. This means that two subscribers in the same building could have numbers starting with different prefixes. The 231 block specifically is part of the 23 range, which was introduced to supplement the older 22 prefix as demand for telephone numbers grew. There are no overlay codes requiring ten-digit dialing; all Norwegian numbers are eight digits long, and the country code +47 is always required for international calls. When dialing from a foreign country, callers should omit any leading '0' (which is not used in Norway) and ensure they have the correct international exit code.
For businesses, having a 231 number signals a local presence in Oslo, which can enhance customer trust and local accessibility. However, with the rise of VoIP and cloud-based telephony, many companies use such numbers for virtual offices, routing calls to any location worldwide while maintaining a prestigious Oslo address. Callers should be aware that calls to 231 numbers are typically charged at standard national rates, and international rates vary by carrier.