You don't need a land line for the Dish to function; you just need a land line to buy pay-per-view and things like that.
DirecTV TELLS you that you need a land line, but it's a dirty little secret that you don't.
Interestingly, years ago, when my dish was being installed, the installer told me that if you don't have the phone line hooked up, you can still order PPV, receive the PPV, but you won't be BILLED for the PPV until you plug in your receiver to the phone line. I have no idea whether or not this is true because I never tried it, but it's an interesting bit of information that, for some reason, I haven't forgotten.
That statement was true then, probably still is. I haven't been plugged into a phone line for years and I still have two movies that should be paid for from about 3 or 4 years ago. You can find them in one of the menus. Kids figured out they could watch FREE movies. I pointed out the falacy of their thinking when I discovered what they were doing.