Dial `*67` before the phone number you want to call
On iPhone, go to `Settings` > `Phone` > `Show My Caller ID` and turn it off
On Android, open the Phone app, go to `Settings` > `Calling accounts` or `Supplementary services` > `Caller ID`, and choose `Hide number`
Use your carrier’s caller ID blocking feature if available
Contact your mobile carrier to request permanent caller ID blocking
Use a VoIP app or service that supports hidden caller ID
Check the recipient’s country or carrier, since caller ID blocking may not work everywhere