I recently got Sky+, and really didn't want the phone line connected, as it would have been unsightly.
When the engineer arrived, I said that I didn't want it, and he said that it was no problem.
He installed the system in 15 minutes with the phone line plugged in, then unplugged the wire from the phone, rolled it up and put it behind the TV in case we ever need it.
I'm not sure why you need it, but possibly to purchase movies or play games, in which case you can just plug it in for as little or as long as you need.
The red button still works without the line connectd, as the engineer told me that all of that information comes through the dish.
So in summary, you definitely DO NOT need a phone line permanently plugged in.