I have the whole Sky package....sky+ (everything except the sports), wireless broadband and free UK telephone calls. I get all of that for �55 per month (which is excellent considering I was �44 just for my sky package before and �40 per month for my phone and broadband from BT before).
When I changed from BT to Sky for everything, I had a BT landline number already so I'm not very sure how you should go about getting that sorted, as if you call BT for a number, you'll have entered into a contract with them for 12 months.
Saying that, I still have to pay BT my line rental, so maybe the contract is novated across to Sky, which means if you do have to enter a contract with BT, you won't be breaking it if you go with Sky.
The best thing you can do is to call Sky and check that they provide a broadband service in your area and take it from there.