You can prevent your number from appearing on a recipient's phone or caller ID device when you place a call. On either your traditional landline or mobile smartphone, just dial *67 followed by the number you want to call; the person you're calling will only see a message such as "blocked" or "private number" when their phone rings.

*67 does not work when you call toll-free numbers or emergency numbers including 911.

How to Use *67 on an Android Phone

While using *67 works on smartphones, most cellular carriers offer an easier way to block your number through the Android or iOS device settings. To hide your number while using an Android phone:

Tap the Phone icon, usually found toward the bottom of the screen. Locate the Search bar on the Phone interface and tap the three vertically aligned dots found within it to display a drop-down menu. Select Settings from the drop-down menu. Tap the Calls section. Tap Additional settings. Tap Caller ID. Tap Hide number when the pop-out interface is displayed.

How to Use *67 on an iPhone

To hide your number when you use an iPhone or other iOS device:

Tap the Settings icon on your device's Home screen. Scroll down in the Settings interface and select Phone. Tap Show My Caller ID in the Calls section. If the button on the Show My Caller ID screen is in the green on position, tap it once so that it turns white, which is the off position. Your outgoing calls will now display with the message "No Caller ID" in place of your phone number.

How to Use Other Popular Vertical Service Codes

The following vertical service codes work with most popular providers. Check with your phone company if a particular code is not working as expected.

*60 : Provides the ability to block a specific number.

: Provides the ability to block a specific number. *66 : Continuously dials a busy number until the line becomes free.

: Continuously dials a busy number until the line becomes free. *69: Useful from a landline that does not have caller ID, this code dials the last number that called you.

Useful from a landline that does not have caller ID, this code dials the last number that called you. *70 : Temporarily deactivates the call waiting feature.

: Temporarily deactivates the call waiting feature. *72 : Enables call forwarding on a landline.

: Enables call forwarding on a landline. *77: Enables anonymous call rejection, which only allows incoming calls from people who reveal their number.

Why Use *67?

Now a common feature on most home phones and virtually all mobile devices, caller ID gives us the ability to screen calls and avoid annoying friends or pesky telemarketers. An obvious downside to this functionality is that anonymity when placing a call is now a thing of the past. Fortunately, vertical service codes like *67 can come in handy if you need to call people who you don't necessarily want to call you back. For example, if you need to call a business client after work hours from your personal phone, you might not want them to have that number. Just keep in mind that some people choose to block hidden or private numbers from calling them automatically, in which case your call won't go through if you use *67.