To view/send texts you need a BT line, an SMS compatible phone and be subscribed to Caller Display. It will not work on NTL regardless of caller display availability, end of story. I doubt NTL have any plans for it.
Yet another reason why I've got BT now
However, as said, you can received voice-mail versions on a landline via the service BT provide, though I'm surprise BT forward it to an NTL line.