What Is a Withheld Number Call?
When your phone displays "No Caller ID," "Unknown," or "Private Number," it means the caller has hidden their phone number. In Japan, dialing 184 before a number prevents it from being displayed to the recipient.
While some legitimate callers (hospitals, schools) use this feature, withheld numbers are frequently used for nuisance calls and scams.
Who Calls from Withheld Numbers?
Telemarketers and Sales Calls
The most common type. They hide their number to avoid being blocked. Real estate, internet service, and investment pitches are typical.
Scam Calls
Fraud callers hide their identity using withheld numbers. Anyone claiming to be "police" or "your bank" on a withheld number is suspicious.
Silent and Prank Calls
Calls where no one speaks or prank calls also commonly use withheld numbers.
Legitimate Calls
Hospitals, teachers, and recruiters sometimes call from withheld numbers, but they usually warn you in advance.
Should You Answer?
Generally, no. If it's important, the caller will call back with their number shown or leave a voicemail. The exception is when you're expecting a specific call that might come from a withheld number.
How to Block on iPhone
Go to Settings > Phone > Silence Unknown Callers. This sends withheld and unknown calls to voicemail while keeping them in your call history.
How to Block on Android
Open the Phone app > Menu > Settings > Blocked numbers > Block unknown callers. The exact path varies by manufacturer.
Carrier Blocking Services
Japanese carriers offer network-level blocking: NTT Docomo and au provide free services that play a guidance message asking withheld callers to show their number. SoftBank offers "Number Block" for 110 yen/month.
If You Accidentally Answer
Don't panic. Never share personal information, ask "Who is calling?" instead of just saying "yes," and hang up immediately if anything feels suspicious.