BB, Let me give you a hypothetical situation then. Assume I am using a cell phone with pre-paid SIM in it. I call you and give you a life threat. :P Obviously, you can see my number in your cell and try to track it. But I just took that SIM card out and threw it in the gutter. I bought a new pre-paid sim card. (A pre-paid sim card costs just some hundreds bucks.) Now, how you gonna track my number in that case? :)