I think Virgin is broadband, phone and TV via a ground cable (streets dug up) and thus you have to be in a Virgin ''area''
Vodafone uses lines via Openreach for Fibre and phone line - same as BT (also provide ADSL Broadband and Fibre for SKY, Talk Talk and Plusnet who all basically rent the lines off Openreach)
Sky can offer a package for line rental, anytime calls (so no more BT contract) and Fibre broadband for under £50pm on their current offers.
Offers are usually valid 12 18 or 24 months - after that time shop around
Always found SKY service to be good and Tech back up is all in the UK. You don't have to have SKY TV.