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 similarly allocated in blocks of 10,000 to each carrier. Toll-free numbers (0120) and IP phone numbers (050) are also allocated by number block to carriers. As of 2024, approximately 740 million mobile phone numbers have been designated.
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 is a serious issue in urban areas. Available landline numbers in Tokyo (03) and Osaka (06) are dwindling, making new allocations difficult. For mobile phones, the 090 block is already exhausted, and 080 and 070 were opened in succession. The opening of the 060 block is also under discussion. The Ministry's Telecommunications Number Designation Database allows anyone to check which carrier holds each number block. See Phone Number Structure Guide for an overview of the numbering system.