TBH I'm not sure NTL: TW has any plans to bring in a VOIP service. The problem is that a fair chunk of their revenue is from the phone line they bundle in so they'd be volunteering to lose a big chunk of revenue.
I reckon to make the money back they'd shift from speed based broadband packages to capacity based. i.e. Everyone gets the same speed but you pay for what do download/upload. At which point I'm completely screwed - I can't go to ADSL because I live on the boundary between two exchanges so am guaranteed nothing more than a ****e signal.