This is how they should encrypt things. You call dish (or directv) and say you want a programming package, you then punch a code in the receiver they give you. Your receiver then dials directv with that code, to confirm that is your receiver. Then they send a code back to your receiver, that is speicfic to your receiver, allowing you to watch tv.
you'd piss off alot of people who dont have their receivers hooked to a phone line because they dont have a landline. According to your "theory" you need a phone line hooked up at all times