Phone number recycling is a system where canceled phone numbers are reassigned to new subscribers after a cooling-off period. Phone numbers are a finite resource, and in urban areas where number exhaustion is advancing, reusing unused numbers is unavoidable. Carriers manage the cooling-off and reassignment process under the Ministry's Telecommunications Numbering Plan.
When you receive a recycled number, calls and SMS intended for the previous owner may arrive. This is especially serious when the previous owner registered the number with various web services. Two-factor authentication codes could be sent to the new owner, potentially granting access to the previous owner's accounts. Conversely, if the previous owner had debts, debt collection calls may repeatedly reach the new owner.
Carriers set a holding period before reassignment, but its length is left to each carrier and often does not appear in published terms of service. The Ministry of Internal Affairs and Communications review criteria (revised in 2019) under the Telecommunications Business Act only require carriers to reuse numbers where possible and to "set the holding period appropriately in light of user convenience" - no nationwide figure is prescribed. There is therefore no general rule for how many months pass before a number returns to circulation. Where number exhaustion has left little spare inventory in a block, a long holding period is harder to maintain, so reassignment can still happen before the previous owner's traces have fully cleared.
As a precaution before canceling a number, it is important to update the phone number on all registered services. Banks, social media, e-commerce sites, and services with two-factor authentication are top priorities. If the new owner continues to receive calls for the previous owner, they can contact their carrier to request a number change. Using number portability to keep your number when switching carriers avoids the recycling issue entirely. See Phone Number Privacy Tips for specific measures.
- What goes wrong - two-factor authentication codes and notices from services still registered to the number flow to whoever receives it next
- What to do - update the phone number on every registered service before canceling, starting with banks, social media, e-commerce sites and services using two-factor authentication
- What goes wrong - calls and SMS for the previous owner keep arriving, and if that person had debts, collection agencies call repeatedly
- What to do - if the calls continue, contact the carrier and request a number change