Under your agreement with Dish Network you must have a phone line or broadband connected to your receiver at all times.
By having it hooked up the receiver reports home every so often and reports PPV purchases, signal levels, and its also possible to report back viewing habits.
Why didn't you mention the main reason, receiver location. As far as what if you don't have a land line or broadband, pay up the $5 extra per month for no phone hookup and if it's not a "no phone line" fee, well, they'll sock you for a "solo receiver" fee of $5 each per month. Thank you Dish Network, the king of the add-on fees.
Nick