Area Code 51 – Mobile Network
The phone area code for Mobile Network is 51 (international format +4551). Browse local exchange codes (NXX) and carrier assignments below.
📞 Exchange Codes (NXX) for Area Code 51
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Overview of Danish Mobile Prefix 51
In Denmark, the national dialing plan follows the ITU-T E.164 standard, with the country calling code +45. Unlike many countries that use area codes for fixed-line telephony, Denmark employs a closed numbering plan with no trunk prefix. All subscriber numbers, whether fixed or mobile, are eight digits long. The prefix 51 is allocated to mobile network services, meaning it is non-geographic and not tied to any specific region or city. Numbers beginning with +45 51 are used exclusively by mobile network operators (MNOs) and mobile virtual network operators (MVNOs) operating in Denmark.
Technical Characteristics and Numbering
Danish mobile numbers are always eight digits in length, and the prefix 51 is the first two digits of the subscriber number. For example, a complete number might be +45 51 23 45 67. When dialing within Denmark, you must include the full eight-digit number, as there is no local dialing format with a separate area code. From abroad, you dial the international access code (00 or +), then 45, followed by the eight-digit number. The prefix 51 is not an area code; it is a service identifier indicating a mobile subscription.
Mobile numbers in Denmark are portable. This means that a subscriber can switch from one MNO to another while retaining their number, including those starting with 51. Therefore, the prefix does not necessarily indicate the current network operator, only that the number was originally allocated to a mobile service. For routing purposes, the Danish Numbering Plan assigns ranges to specific operators, but portability requires databases to determine the current network for call termination.
Usage and Dialing Instructions
Numbers with prefix 51 are used for voice, SMS, and mobile data services. They are non-geographic, so they are not associated with any physical location. When calling a Danish mobile number from abroad, you must use the international format: +45 51 XX XX XX (or 0045 51 XX XX XX). From within Denmark, simply dial the eight-digit number, e.g., 51 23 45 67. There is no need to add a trunk prefix like '0' as is common in other countries.
For international callers, it is important to note that Danish mobile numbers are not reachable via any special access codes. The call is billed according to the caller's international tariff, and the receiving party may incur charges depending on their roaming or subscription plan. For SMS and MMS, the same international format applies.
Regulatory and Operational Context
The Danish Business Authority (Erhvervsstyrelsen) oversees the national numbering plan. Prefixes are allocated to operators in blocks, and the 51 range is among those used for mobile services. Operators such as TDC, Telenor, Telia, and 3, as well as MVNOs, may hold allocations within this range. Because of number portability, the prefix alone cannot be used to identify the operator definitively.
In summary, +45 51 numbers are Danish mobile numbers, non-geographic, and require international dialing format when calling from outside Denmark. They are an integral part of Denmark's modern telecommunications infrastructure, supporting both personal and business mobile communications.