Well, ask Sky and they'll probably say yes on all counts, but in reality you only need to connect your Sky TV box to a telephone line if either of the below two reasons apply to you.
You WILL need to connect your Sky box to a telephone line if....
Subsidised Sky TV Box
If you purchased your Sky TV box from Sky at a reduced cost (subsidised) or were given a box free of charge then you will need to connect it to a telephone line for the first 12 months, after 12 months you can disconnect it from the phone line if you wish providing the second reason below does not apply.
Sky Multiroom
Sky Multiroom is where you have two boxes with separate viewing cards but running on the same account. Because Sky give you the same package on both TV boxes, the first at full price and the second at a reduced cost of £10 per month, Sky insist you connect both boxes to the same telephone line, by doing this Sky can monitor the boxes in as far as they know they're still in the same property. It prevents customers for example from getting Sky Multiroom then giving one of the boxes and cards to a friend or relative to use at a reduced cost (£10 per month). Both boxes will call Sky roughly every 30 days to let them know that both are still connected, this is called a "Callback", if one or both boxes do not carry out the automatic Callback Sky will send you a letter asking you to connect them both to the phone line on your contract, after a while if you do not do as Sky ask they will start charging the full subscription charge that you subscribe to for both boxes.
You will NOT need to connect your Sky TV box to a telephone line if...
You purchased a non-subsidised box from an independent retailer such as us.
You originally had a subsidised Sky TV box from Sky but a year has passed since you took your contract out with them.
You do not have Sky Multiroom, Sky Multiroom installations must have all boxes connected at all times.
If you end up buying your new Sky TV box from an independent retailer other than us please make sure you get it in writing that the box is definitely non-subsidised, this is because some retailers sell subsidised boxes as non-subsidised, if you end up with one it could cause problems with Sky when you come to pair your card to the new box.
