As of 2014, the most common way to block outgoing calls using AT&T is to dial *67 on your device plus the 10-digit phone number. To hide your number on all outgoing calls, check to see if your device contains the ability. AT&T can add or remove the service free of charge, and it can be set up within just a few minutes.Know More
Go to AT&T's Device How-To Center located on their website and choose your device. Click on Device Instructions, and select Calling Options under the calling features menu.
Look through the instructions of the calling options. If there is no section for Caller ID instructions, your device may not have the ability to hide all outgoing calls. Your number can still be blocked on a call-by-call basis by dialing *67 before making a phone call.
Update the Caller ID settings according to the directions provided for your device to block all outgoing calls. This setting is effective until it is changed.
If your device is unable to hide your number on all calls, contact AT&T to add the feature to your service.
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