A service you can use, to identify restricted, blocked, unknown callers is
www.trapcall.com.
You sign up, and when a restricted call comes in you "ignore" the call, then it in the easiest way to explain "magically" reveals the callers ID.
You get a free trial period, then after that you have to pay. I recommend everyone try the free trial, just for educational purposes. It is somewhat scary, as many people block thier numbers when making calls. If you call some blocked, and they unblock with this method, there is NO indication to the calling party that you have unblocked their call.