A numbering plan defines telephone number structure (digits, format, purpose) and allocation rules. Japan's Ministry of Internal Affairs manages the "Telecommunications Numbering Plan," handling area code assignment, mobile number allocation, and special numbers like 0120/0570.
Japanese numbers follow "0 + area code + local code + subscriber number": 10 digits for landlines, 11 for mobiles (090/080/070 + 8 digits). This conforms to ITU-T E.164; international calls use country code "+81" dropping the leading 0.
Running out of numbers is a serious problem. The 090 block alone stopped being enough, so 080 (from 2002) and 070 (from 2013) were opened for mobile use. The Ministry's published number assignment records show that, as of 2026, no assignable numbers remain in the 090 and 080 blocks and more than 90 percent of the 070 block has been assigned to carriers. Faced with that pressure, the Ministry amended the Telecommunications Numbering Plan in December 2024 to add the 060 block for mobile phones (the launch originally planned for July 2026 onward was postponed and had not begun as of August 2026). The 0120 block is likewise almost fully assigned, which is why the 0800 block was introduced as an alternative.
Plans evolve with society: MNP introduction, 050 number creation, and PSTN migration numbering reviews. See phone number structure guide and number length history.