Key problem here: are you plugging your router into your NTL phone line?
Cable phone lines come over the same cable as the TV and the broadband.
adsl (such as AOL, BT etc) comes over the BT phoneline to the exchange.
You cannot get ADSL over a cable phone line.
My opinion? If you want a cheap, all-in-one solution go for cable-everything. Phone, TV and broadband. NTL will no doubt be able to sell/give you the equipment required when you subscribe.
If you want optimal performance, go for separates: Sky TV, BT phone, ADSL broadband. Costs a little bit more per month, but you can do without the download limits, get more TV channels etc.