Number exhaustion refers to the problem of running out of available phone numbers. Phone numbers are a finite public resource, and demand has repeatedly outstripped supply as telecommunications services have expanded. In Japan, the explosive growth of mobile phones has been the primary driver of number exhaustion.
The history of mobile number exhaustion is also a history of expanding number blocks. In 1999, the 090 block (approximately 80 million numbers) was exhausted, and the 080 block was added. In 2013, the 070 block was opened for mobile phones following the decline of PHS services. Currently, the combined 090/080/070 blocks provide approximately 270 million numbers, of which about 190 million are subscribed, reaching a utilization rate of roughly 70%. With growing demand for IoT device numbering, the opening of the 060 block is under consideration.
Landline numbers have also experienced exhaustion. In major metropolitan areas like Tokyo (03) and Osaka (06), population concentration and corporate density have strained area code capacity. Countermeasures have included changing the number of digits in local exchange codes (Tokyo's local codes expanded from 3 to 4 digits) and assigning new area codes. However, since landline subscriptions are declining, the situation is currently less critical than for mobile numbers.
The key to addressing number exhaustion lies in flexible management of the number allocation system. The main tools are recovering unused numbers (returning allocated but unused blocks), promoting number recycling (reassigning canceled numbers), and opening new number blocks. The 020 block was established in 2017 for M2M (Machine to Machine) communications, with 11-to-14-digit numbers assigned to IoT devices. See History of Phone Number Digit Lengths for the evolution of the numbering system.