Switching from a bundle

I have a 12 month contract with Homecall (now Pipex Homecall) which
expires in January. It's a broadband and calls bundle with line rental
all paid together. I want to get my broadband elsewhere, I don't mind
making savings by going with someone like Virgin or Tiscali for
broadband and calls (I don't make many calls) but I'm confused about the
line rental. Does that revert to BT when I cancel with Homecall - if the
new provider doesn't do the line rental deal? I can see options on the
BT website to transfer calls back to BT but not simply the line rental.
Or am I just being obtuse here?

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D Marshall