Many of us have received a phone call from someone who has blocked their number from the caller ID. If you are not comfortable accepting these types of calls, then do not answer them. Let your voice mail answer and screen the call. If calls are just annoying, you may be able to get your phone company to help you trace them. If they rise to the level of harassment or threats, the police can help you identify the callers.
Contact your phone service provider and give them the details of the call, such as when it was received. The phone company can trace the call back to the originating number. If it is a cell phone number that is under contact through their company, they may provide you with the name and number belonging to that phone. However, some phone companies require you to fill out a complaint form through their asset protection department. Once you have filed the complaint, they will provide you with the information necessary to file charges or request a block on the number.
If the calls qualify as harassment, you can file a complaint with your local police department. They can contact your phone service provider and ask them to investigate the calls made to you. However, getting the police involved means that you must be willing to file formal charges.
You can hire a private investigator to trace the source of the blocked ID calls. This is the most expensive option, but it could produce the results you want and find the information you need much more quickly. The private investigator will work through your local police or phone company investigators.