What it means
Anyone can legally block the transmission of their number, so the call appears as “unknown”. The FCC is explicit that this is not spoofing. Federal law protects the right to block caller ID. On a Verizon home phone, a call made after dialing *67 shows “Private” or “P”.
There is one exception: anyone making telemarketing calls is prohibited from blocking caller ID, and must show a number (and, if possible, the name of the company) on whose behalf they call. A sales call with no caller ID is breaking that rule.
How callers hide their number
Dialing *67 before a number asks the carrier not to pass the caller's number on that call, and *82 asks it to pass the number on a line that hides it by default. Carriers may not charge for per-call blocking. Blocking works call by call, and some calls cannot be blocked at all, such as calls to 911 and to toll-free numbers.
Carriers must honor the caller's choice: T-Mobile says it cannot block anonymous calls or override a caller's privacy choice, but that you can choose not to accept them.
The star codes
These are vertical service codes defined by the numbering industry; availability depends on your line and carrier.
| Code | What it does |
|---|---|
| *67 | Hides your number for the call you are about to make. Per-call blocking must be free. |
| *82 | Shows your number on a call when your line hides it by default. |
| *77 | Anonymous Call Rejection: rejects calls from callers who hide their number. *87 turns it off. |
| *69 | Calls back the last number that called you. *89 cancels it. |
| *57 | Call Trace: asks for a trace of the last call, for obscene, harassing or threatening calls. |
How to reject or silence these calls
- Landline: Anonymous Call Rejection (*77 on Verizon home phones) stops calls from blocked numbers ringing; the caller hears that you do not accept blocked calls. If someone with *77 is called from a hidden number, the call is not answered.
- Android (Phone by Google): Phone app, More, Settings, Blocked numbers, then turn on “Unknown”. This blocks private and unidentified numbers; numbers that are simply not in your contacts still ring. With fake call detection, Android can also alert you when a caller hides their identity or impersonates a contact.
- iPhone: Settings, Apps, Phone, Screen Unknown Callers, then choose Silence (sent to voicemail) or Ask Reason for Calling.
- AT&T: in the ActiveArmor app you can allow, block or send private callers to voicemail.
More options are in how to block robocalls.
Threatening calls
For obscene, harassing or threatening calls, Call Trace (*57) asks the carrier to trace the last call received. On Verizon home phones, charges may apply and trace records are released only to law enforcement. If you are in danger, call 911.