The “landline” bit is a red herring, you need a phone line that has a socket type connection like BT’s or B4RN’s which is not available on a mobile phone hence the “landline” tag.
Yes you need a phone line to be able to access the Sky services BUT it can be a B4RN phone line not a BT one.
That will work in exactly the same way with a B4RN system. There is a small box that has one or two phone sockets on it. You plug your sky lead into one of the sockets and then plug your phone into the empty socket on the Sky cable. A B4RN VoIP line will look exactly the same to Sky as a BT landline does. You would normally plug the phone lead from the Sky box into the phone’s wall socket and then plug your phone into the empty socket on the Sky cable. Or, if you don’t want a home phone at all, Sky say: “You cannot have the multiroom option if no landline so the TV can only be in one room, and you lose two interactive options – buying a Box Office movie or event and checking your bill through your Sky+ box. Both of these can be done by calling a local rate 0844 number.”Forum with some great tips for Sky without a phone: http://forums.moneysavingexpert.com/showthread.php?t=981185