Phone Numbers Are a Finite Resource
Japan's mobile phone numbers across 090, 080, and 070 total approximately 270 million. As of March 2024, about 190 million have been allocated - roughly 70% of the available space. Since numbers are not infinite, canceled numbers are reassigned to new subscribers after a dormancy period. This is "number recycling."
Landline numbers are also recycled. In Japan's numbering system, landlines are 10 digits, and in urban areas where demand is high, canceled numbers are reused relatively quickly. Tokyo (03) and Osaka (06) numbers are in particularly high demand.
How Number Recycling Works
Dormancy Period
Canceled numbers are not immediately reassigned. Carriers maintain a "dormancy period" (cooling-off period) during which the number sits unassigned. This typically lasts 6 months to 1 year, depending on the carrier.
The dormancy period exists to reduce the chance of the new owner receiving calls meant for the previous owner. Right after cancellation, the previous owner's contacts and business partners may still call the old number. A waiting period reduces the frequency of such calls, though it does not eliminate them entirely.
Reassignment Process
After the dormancy period, the number returns to the carrier's number pool. When a new subscriber signs up, a number is assigned from this pool randomly or sequentially. Specifying a particular number is generally not possible, though some carriers offer a "number selection service" with several candidates to choose from.
Troubles Caused by Number Recycling
Calls for the Previous Owner
The most common issue is receiving calls and messages meant for the previous owner - unknown callers asking for someone by name, automated messages from services the previous owner registered with, or even debt collection calls.
Particularly troublesome is when the previous owner's number was registered in a spam call database. If so, calls from the new owner may be displayed as "spam" on the recipient's end. Contact the database operator to request removal.
Two-Factor Authentication Issues
If the previous owner registered the number for two-factor authentication, the new owner may receive authentication SMS codes. This is not just an annoyance but a security risk - the new owner could potentially access the previous owner's accounts.
To prevent this, before canceling your phone, update or remove your number from all services that use it for two-factor authentication - banks, social media, email, e-commerce sites, and more.
Debt Collection Calls
If the previous owner had debts, collection agencies may call the new owner. Clearly state: "I recently obtained this number and do not know that person." If calls persist, consider reporting nuisance calls.
How to Avoid Changing Your Number
- MNP (Number Portability): When switching carriers, use MNP to keep your number. No recycling occurs
- Suspension: If temporarily not using the line, suspend rather than cancel. NTT landlines can be kept for a few hundred yen per month
- Long-term retention: Keeping the same number builds trust associated with it, especially important for business use
Number Exhaustion and Future Outlook
With 70% of mobile numbers already in use, future exhaustion is a concern. The MIC is considering opening the 060 band (adding ~90 million numbers). The 020 band has been allocated for M2M/IoT communications, separating device numbers from human-use numbers.
Number recycling is a rational system for efficiently using finite number resources. However, troubles from calls meant for previous owners cannot be completely eliminated. Thorough phone number privacy management - removing your number from all services before canceling - protects both yourself and the next user. Smartphone security products are also worth considering.
Number Recycling and Nuisance Calls
Number recycling is closely tied to the nuisance call problem. If the previous owner was a habitual spam caller, the number may be registered in spam databases and block lists.
What to Do If You Get a "Dirty Number"
- Request removal from spam databases: Contact major databases like Whoscall with proof of new ownership (copy of contract) to request delisting
- Contact your carrier: Request a number change. Carriers may waive the fee given the circumstances
- Use caller ID: Call with your number displayed (not blocked) to show recipients you are a legitimate user
The Reverse: Previous Owner Was a Spam Victim
If the previous owner was a spam victim, you may receive a flood of nuisance calls. Use call blocking methods and consult your carrier about a number change if the situation does not improve.
While completely preventing recycling-related troubles is difficult, basic measures from the mobile phone FAQ can minimize the impact. After getting a new number, check whether it is registered in any spam databases and address issues early. 090 numbers have a longer history and may have been recycled more times, so extra caution is warranted.