Network use restriction (○ / △ / × status)

ネットワーク利用制限 nettowāku riyō seigen

A carrier's power to block a specific handset from its network by IMEI — used mainly when a device bought on instalments is not being paid for, or is reported lost or stolen. A used phone is commonly graded ○ (clear), △ (instalments still being paid) or × (restricted / blocked).

The status is tied to the handset's IMEI, not to the SIM or the current user. A phone sold second-hand can be restricted later if the original buyer stops paying their instalments, so △ carries real risk for a buyer. Each carrier publishes an IMEI look-up page where you can check the current status before buying or accepting a used device.

If you buy a phone outright, or finish the instalments, the status should move to ○. Some carriers have moved toward not restricting a phone purely for unpaid instalments (billing the balance instead), but a lost/stolen report can still block it. Buying from a shop that guarantees a ○ status, in writing, avoids the problem. This is separate from a SIM lock, which limits which carrier's SIM a phone accepts.