Longweight – if you have cable to your door, you don’t need a landline. However, Virgin also offers a DSL option for those outside the cable footprint (about 49% of the UK), which will need a landline. DSL is pushed over the copper (or sometimes aluminium) lines originally installed by BT for voice.
Landline usage is falling steadily, because people tend to just use mobiles or VoIP instead of circuit switched voice. People get landlines purely for the broadband connection – I’ve done it myself. It’s a huge problem for the companies that own this stuff.
AS Cynic-al says, you can (and should) haggle like hell. I saved £60 a year on my Virgin connection – landline, M TV package and XL broadband for £28 a month. It would have cost more if I’d said no to the phone line. 😆