If on the phone itself, that is usually a blocked or restricted number. The caller does not want the receiver to know who it is
There is a site named trapcall.com which offers a pay service to let you know who or what the number is to.
Cant Verizon tell me who it is?? I tried a bogus pay site for something else and it told me nothing and I had to cancel the service immediately. I am having suspicious issues I am trying to get to the bottom of ...
No, if the number is blocked from the sender's phone, then all you will see if "blocked" , "restricted", or "unavailable" when the call comes in, and your bill will show all 9's.
Trapcall will tell you what the number is - but as budone said, it is a pay service, not free.