If someone is calling you and the number is showing up as "unavailable" or "restricted," it can be a frustrating experience--especially if the withheld number calls are hang-ups or other kinds of harassment. One way to deal with the annoying calls is to activate a block for unknown callers through your telephone service provider. This will force the caller to call you on an identifiable number. However, if you want to trace a number, you do have options.
Dial *57 immediately after you hang up the receiver. An electronic voice will give you instructions on how to trace the number. Once you have three successful traces for the same number, call your service provider's annoyance call bureau to report the number.
Type "anonymous call tracing" into your Internet browser. There are many products available that can locate and trace anonymous numbers, sometimes for free. These services access a phone number database and can work with a wide variety of cell phone providers.
Visit your local police station and fill out a complaint form. Many service providers will require that you perform this step before they will investigate annoyance calls: check with your service provider for their specific policy. Provide as much information as possible to the police, like the time of the calls, what the caller said, if there was background noise and as much information about the caller's voice as possible. For example, if he sounded intoxicated or if he had a speech impediment.
If the caller is threatening you, do not wait for three successive calls: call the annoyance call bureau immediately.