2 reasons for phone lines with Sky. I don’t know why they aren’t transparent about this, because I’ve no problem with either.
1st is because the box is subsidised by a marketing company, as andy has said. If you don’t want that subsidy, fine, you don’t have to take it. Sky, Sky+ and Sky HD can all be installed without a phone line once you pay the subsidy difference. Yes, Sky could have been more upfront about this, but then most people simply do not give a damn and prefer to save the â‚¬35 charge, including myself.
2nd is for Sky Multiroom subscriptions (where you get a second or subsequent box that shows all the Sky channels you have, including premium channels, that you have on your main/first Sky box) for â‚¬15/month. The phone line is required to make sure you’re not farming off the subsidised box to your neighbours/friends/English cousins/Tenerife holiday home (which happens to be a bar). Fair enough. If you subscribe to Sky Movies or Sports, you’ll know that that is a pretty decent subsidy. Again, if you don’t want he subsidy, no problem. Just pay for a separate Sky box instead.
Updates are done over the air on all modern Sky boxes, and not over the telephone. Multiroom boxes phone home on demand (random times, to make sure all are still connected to the same phone line) and are to a freephone number (and usually in off-peak times to avoid clash with phone use).
For all other uses of the phoneline (both paid, and freephone) you’re clearly advised of the charge before going online.
I haven’t heard of anyone getting letters from Sky for disconnecting Sky, Sky+, Sky HD (in the first year, as per contract), but I have heard of plenty of letters for Multiroom boxes not being connected (which is more serious, I guess).