The Bad News
Unfortunately, when you get "blocked" calls, the information isn't sent from the phone company to your caller id box or phone, just a message saying that the number has been blocked. Because it wasn't sent in the first place, there's no way to program a device to show you what it is. The Good News
Quite often, those silent callers
are tele-marketers. The machines they use to call people dial dozens of numbers at a time, and when they get a live caller, they connect it to a person, who tries to sell you carpet cleaning, change your long distance provider, or give you an excellent rate on a new pre-approved credit card.
Some times, though, they get too many live people, so their system keeps hunting for an available operator, leaving you with nobody to talk to. That's likely what you are getting. Short of blocking unknown callers, if your phone service allows for that, I'm afraid I don't know of an easy way to stop it.
That said, there is a service, commonly called "Call Trace", which most phone providers give you, that doesn't give you the number, but instead records it, where it can be retrieved by law enforcement agencies. If you are getting a lot of these, you can enter the code to "trap" the call, then follow up with law enforcement or the phone company to put a stop to it. The phone company may charge you for each call, so you should check with them about it first.
For more information, check out Stopping Harassing Phone Calls
, they have a lot of U.S. and California-specific information there. Final thoughts
You could try "Call Return", (often *69) to call the person back, and see if they are having trouble with the phone on their end. Some cell phones will auto-dial a number if you hold down a single digit for long enough. Someone you know might have your number stored in you cell phone, and it's calling you when they sit down on their phone, without them even knowing about it! I've also got silent calls from friends who need a new handset cord, or when their phone has fallen off the desk one time too many. Usually it doesn't happen very often, especially once they figure out the person on the other end can't hear them.