1) As far as I know, you no longer have to have an ntl phoneline if you have ntl broadband, so you should be fine for that (although they do still have the stupid requirement that you must have an ntl phoneline if you want ntl CATV).
2) If it's the same as everything else, then you have to give 30 days notice of cancellation (unless you are still in the initial 12 month contract - in which case you can't cancel early. EDIT - ah, if you've been waiting for caller ID for 6 years, then you're obviously out of the 12 month contract! I should have read the post more fully)
If you do end up wanting to ditch ntl broadband, then have a look at some of the threads in here (or start your own):
http://www.cableforum.co.uk/board/forumdisplay.php?f=63