Area Code 2388 – Oslo

Geographic Coverage and Administrative Jurisdiction

The Norwegian national destination code 23 88 is a geographic area code allocated within the Oslo numbering zone. It serves the central and eastern districts of Oslo, Norway's capital and most populous city. The prefix is administered under the jurisdiction of the Norwegian Communications Authority (Nkom) and is assigned to fixed-line PSTN and VoIP services operating within this specific geographic area. Oslo's numbering plan is characterized by a high density of exchanges, and the 23 88 range is one of several central office codes that support the city's extensive telecommunications infrastructure.

Dialing Formats and Caller Instructions

For local callers within Norway, the number is dialed in its full national format: 23 88 XX XX. No trunk prefix '0' is used, as Norway employs a closed numbering plan where the country code +47 is always required for international calls. When dialing from abroad, the international format is +47 23 88 XX XX. The country code +47 is mandatory for all calls originating outside Norway, and the leading '23' is the national destination code that routes the call to the Oslo geographic region. For callers within Oslo, it is important to note that the entire 8-digit subscriber number must be dialed, even for local calls, as there are no short local dialing codes.

Numbering Plan and Overlay Considerations

Norway's numbering plan does not use geographic area codes in the traditional sense; instead, the country is divided into numbering zones, and the first two digits after the country code often indicate the region. The 23 88 prefix is part of the Oslo numbering zone, which spans multiple central office codes. There are no overlay codes in Norway, as the country has implemented a unified numbering plan with 8-digit subscriber numbers for all geographic services. This means that number portability is fully supported, allowing subscribers to retain their 23 88 numbers when switching providers, even if they move outside the Oslo area, though the number remains associated with its original geographic allocation.

Technical and Regulatory Notes

From a technical perspective, 23 88 numbers are used for both traditional PSTN lines and VoIP services, with routing determined by the national signaling network. Calls to these numbers are typically charged at standard national rates, depending on the caller's subscription plan. For international callers, the cost is determined by the bilateral agreements between Norway and the caller's country. It is also worth noting that some businesses in Oslo may use 23 88 numbers as their primary contact lines, and these numbers are often listed in official directories. As with all Norwegian geographic numbers, the maximum number length is 8 digits after the country code, and the prefix 23 88 is not used for mobile services, which are assigned separate non-geographic ranges starting with 4 or 9.