Over the past few months we've been getting some annoying prank phone calls from a "Private Caller" REALLY late at night, which isn't good for sleeping toddlers. Calling them back or reporting them wasn't possible due to their blocked number not showing on our Caller ID. I finally called our phone service provider today to see if anything could be done, and they told me about *77.
*77 Stops any calls with blocked numbers from successfully calling our number. Legitimate callers can follow a prompt and unblock their phone number, while those wishing to remain anonymous will not be successful!
So if you want to block Anonymous callers from bothering you, use *77. For me it is a free service, but double check with your service provider to make sure it is included in your phone service!
I wish I had known about this service before!