...or phone numbers, or P.O. box numbers, or the street address of your home or business? All of those are identifiers in addressing systems, for which you have some expectation that they will continue to be maintained for you as long as you pay all applicable bills, but do you have a legally-enforceable ownership right in them? Sometimes the phone company will change your area code on you, or the city council will rename your street or renumber the city's street addressing system, and your address will change against your will.