It depends on why you're doing it
In the United States, the Truth in Caller ID Act makes it illegal to spoof a number "with the intent to defraud, cause harm, or wrongfully obtain anything of value." It does not make displaying a different number illegal on its own. Businesses showing a main line instead of an employee's desk extension, a doctor calling from a personal cell while showing the office line, and people masking a personal number for safety are all ordinary, legal uses. Laws vary outside the US, so check your local rules if you're unsure.
Using someone else's real number as your caller ID without their permission, to impersonate them or make them the target of callbacks, is illegal regardless of the reason behind it — and it's exactly what our blacklist and abuse reports exist to catch.
What Spoofey blocks outright
Regardless of intent, we never allow a caller ID that matches:
- Emergency numbers (911, 112, 999, and similar)
- A number that's the same as the one you're calling
- Any number on our blacklist, including ones reported to us as being impersonated
Learn more
We've written more on how caller ID and spoofing actually work under the hood: What Is Caller ID Spoofing? and What Is STIR/SHAKEN?, the industry system built to verify it. If someone's used your number without permission, see someone is spoofing my number.