I am pretty sure if you move somewhere that isn't NTL cabled, then they'll terminate the contract on the spot with no penalties. Hopefully some nice NTL rep will confirm that soon. If you move somewhere that is NTL cabled, then they can move you (not sure about re-installation costs).
The standard BT fresh installation is about £75 (
http://www.bt.com/lines/lo_na_home.j...K&obsOID=83053)