I found that although I paid BT the line rental, they wouldn't provide free caller ID unless I made chargable phone calls, so in the end I told them to cancel that service.
The only thing I would be wary about doing the transfer to Sky (if it is LLU ing) is that should you wish to change providers after 12 months, you will have to pay BT the reconnection fee of around �100, which I think is ridiculous.
Mind you, BT's ridiculous anyway but there you go !!