Ordering second phone line for Infinity and canceling sky?

I can now get BT Infinity which has a much better upload speed than sky can provide. I want to get a new phoneline in for infinity which is included in the cost of setup.

I would still be keeping my sky line in, as I have 3 more months left on my contract. Will I be charged any fees for dropping that phone line and canceling sky completely when my contract period is up?

I wish to do this as I do not want to loose my broadband when I cancel with sky and have to wait for infinity.