Pressing *67 before dialing a number on a phone prevents the number from which you are calling from appearing on the call recipient's caller ID system. *67 is a useful feature for one-time call blocking. However, it may not work on all mobile phones.
Callers use *67 because they do not want the person they are calling to know their phone number, but they do not want their phone number to be blocked from all caller IDs. However, *67 does not usually work on mobile phones. In order to temporarily prevent your number from appearing on caller IDs using your iPhone or Android device, you can edit the caller ID setting in the Phone Settings of your device. This setting will block your number as long as it is switched to on, enabling you to either block your number for a short time, for one call, or permanently.
If you would like your landline number to be permanently blocked from caller IDs, contact your phone service provider to set up per-line blocking, which blocks your number to all caller IDs unless you press *82 to unblock the number for a particular call.