Thanks for highlighting the different pages so well.
It seems quite odd, since one is likely to consider phone line rental (as it means installation cost may be waived, and also, broadband has 2.50 surcharge if one opts not to rent the line too) when reading about broadband, not to be told about this possible saving.
I haven't been through the order process (as an existing customer, I suspect I'd be redirected to an "upgrade products" page) so don't know if one is prompted for a decision on whether to pay up front and thus save 40ish pounds over the first year, but it isn't in the FAQ and really, I think, should be.
Bit that was more puzzling was the redirect back to packages (more difficult to prove when the page changes before your very eyes, if you even get chance to see it, rather than just the URI).
If you run a business, have a second ISP and backup web hosting...