such as the national Do Not Call Registry. If the problem is bad enough, the police may take a report from you and give you advice on getting a legal order for your phone company to turn information over to you about the withheld number, or they may help you to trace the call themselves. 4 Use programs and applications that route your call to a service provider that can unlock the withheld number. Some programs may use your cell phone to route anonymous calls to the service provider who can then finds out the caller's information and sends it back to your cell phone. Tips and warnings Your cell phone can be programmed to block withheld numbers, and you may be able to request from your land line phone provider to stop blocked numbers. Be aware that some of these services may not follow all privacy laws. Be sure to verify the validity and legality of any service you use to track anonymous calls.