There's something dodgy with pricing going on though.
AAISP offer an ADSL only copper pair for 10GBP/month. The only difference between this and a full telephone service is that there's no dial tone and no telephone number. It's still exactly the same wires as when you go to BT and have the full telephone service. I'm pretty sure they're actually reselling a BT offering.
I think AAISP might put a recorded message on the line - because BT engineers were apt to just take any silent pair instead of following the correct procedure to take an unused pair - AAISP customers would suddenly find their ADSL had stopped working and investigation would discover that part of the route back to the exchange had been disconnected and the wires reused for someone else (probably due to a fault on that other persons line)
IIRC BT charges 19GBP/month for line rental. So they're claiming that it's an additional 9GBP/month to provide the dial tone. (with call charges on top of that) Ofcom appear to be saying that that's excessive and they need to reduce their line rental by 5GBP/month.