Re: Oh well
Or more accurately...
AAISP provide a normal PSTN Line, but then add a feature to nobble its use. They also just happen to charge a bit less for said line, and choose to forgo higher margins others make.
However, other ISPs provide said PSTN line for £10 (like AAISP) but do let you use the phone line for voice calls - it's the same wholesale service, without the nobbling.
In the case of AAISP you are paying for a line you can't use for voice but it's an ordinary line, they have no special sauce.