Yeah, I don't think they are banking on the calls making the money, the line rental (which in many cases costs more than the broadband now) is what makes the dough. So in effect the broadband becomes a loss leader for the line rental (can't see the likes of Talktalk offering £3.25 broadband for a year without the £14.95 line rental coming in).
thats my take on it also.
which is also why we never see half price line rental offers, the half price deals or free for X months is always only on the broadband subs,
So sky loss lead on broadband for tv (and now line rental).
and it seems isp's like plusnet which used to be broadband focused now are using broadband to get line rental subs.
BT Infinity 2 Since Dec 2012