Number allocation is a system in which the Ministry of Internal Affairs and Communications assigns blocks of phone numbers to telecommunications carriers. Based on the Telecommunications Number System enacted in 2019, allocation rules are defined for each type of number. Carriers apply to the Minister and receive number block designations after review. Phone numbers are a finite public resource, and their management is a national responsibility.
The allocation unit varies by number type. Landline numbers are allocated in blocks of 10,000 (e.g., the XXXX portion of 03-1234-XXXX) based on area code and local exchange combinations. Mobile phone numbers (090/080/070) are allocated to each carrier in larger units of 100,000. Toll-free numbers (0120) and IP phone numbers (050) are also allocated by number block to carriers. As of 2026, roughly 265 million numbers across the 090, 080, and 070 blocks have been designated to carriers. That figure counts the capacity handed to carriers, which is not the same as the number of subscriber contracts.
Carriers that receive allocations assign individual numbers to subscribers from within their blocks. It is common practice to assign available numbers sequentially to new subscribers, while canceled numbers are recycled after a cooling-off period. If the utilization rate of an allocated block is low, the Ministry may request the return of unused numbers.
Number exhaustion becomes a problem in the areas and number blocks where demand concentrates. Landline numbers in large metropolitan areas such as Tokyo (03) and Osaka (06) draw concentrated demand, so securing spare numbers is a standing challenge. For mobile phones, designations in the 090 block reached its ceiling, and 080 and 070 were opened in succession; 080 has since reached its ceiling as well, and little room is left in the 070 block. The 060 block has also been formally added for mobile phones by a December 2024 amendment to Japan's numbering plan (the launch, originally planned for July 2026 onward, has been postponed and had not started as of August 2026). The designation lists published by the Ministry of Internal Affairs and Communications let anyone check which carrier each number block has been designated to. See How Japanese Phone Numbers Work for an overview of the numbering system.