It can be irritating to receive a call with a blocked caller ID (which might display as "Unknown," "Blocked," or "Restricted" in the caller ID of your cell phone). You don't know if it's a call you don't want to answer, such as from a telemarketer, or from a business or person whose call you've been expecting. There are several techniques and services you can use to trace the name and/or phone number behind a blocked call, some of which are free.
Let the call go to voice mail, then listen to the message. Often, people who've blocked their caller ID will leave their name and phone number in a voice message.
If the person with the blocked caller ID didn't leave a voice message, call back the number by pressing the "Redial" button on the keypad. (The blocked call must be the last incoming call made to your cell phone.) If a person answers, explain that you received a blocked call from that number and ask the person's name. If you get a message recording, a name and/or phone number might be on it. If your phone doesn't have a Redial button, check under the "History" or "Incoming Calls" feature and call the blocked call entry, or contact your cell phone manufacturer (whose number is on its website) and ask if there's a redial feature on your phone model.
Use an unblocking (also called unmasking) service that identifies the name and/or phone number associated with blocked calls. One such service is Trapcall that works on all cell phones and offers different unmasking services for varying monthly fees. For a free trial, go to Trapcall.com, press the "Try Trapcall free!" button on the lower right of the Web page and follow the instructions.
If you're receiving harassing calls from a blocked caller ID, contact your cell phone provider (whose number is on your monthly statements as well as on the main page of its website). Many cell providers will change your number at no charge if you're receiving harassing calls. Some also have corporate security departments that will work with you to to stop the harassing calls. Consider also filing a report with your police department (forward them the dates and times of the calls, as well as the messages).