Dial `*67` before the 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`, then turn off caller ID
Contact your carrier to request permanent caller ID blocking
Use a third-party calling app with caller ID blocking options
If needed, add `#31#` before the number in some countries