How to Trace a Withheld Number on AT&T Phones
Although caller identification, also known as Caller ID, is a common feature that is available on most phones, there are several ways in which callers can block and withhold their information from you. In turn, you will see "Unknown," Private" or "Withheld" displayed on your Caller ID screen. AT&T has services and features that will not only allow you to trace these calls, but also prevent callers from reaching you without first identifying themselves.
Activate AT&T's "Call Tracing" feature by press *57 on your phone. Be sure to utilize this feature immediately after receiving the phone call with the withheld number as it will only work on the last call received.
Listen to the short announcement, then press "1" to trace the call. Keep in mind that a toll free number will be listed during the announcement. This number allows you to file a complaint with your local law enforcement agency if desired. Note that not all calls are successfully traced, and you will receive an error message if the withheld number cannot be traced.
Utilize AT&T's "Anonymous Call Rejection" service by pressing "*77" on your phone. When you activate this feature, all callers who withhold their information will be greeted with a message stating that the number dialed does not accept unidentified calls. The caller must then either call from a phone that publishes its number, or unblock the withheld number.
Contact AT&T and sign up for the "Privacy Manager Service," which allows you to accept or reject incoming calls. Be aware that a message will appear on your phone that allows to take the call, or to send it to an automated message. Reject any calls with a withheld number, and the automated greeting will be sent to the caller advising them to state their name before the call goes through. If the caller refuses to identify his or her name or number, the call will be disconnected.