If I could keep changing my phone so it would transmit the MINs and ESNs of legitimate subscribers, then my calls would be completely safe: every attempt to trace a call would lead to some stranger, the person who owned the real phone associated with the ESN that I was using at the moment. (Okay, the customer would also have to explain to the phone company that he hadn’t made the extra calls he was being charged for, but he wouldn’t be responsible for paying the charges for those unauthorized calls.)