Theoretically BT have a special rate for people who don't make many calls; lower rental and a slightly higher price per call. In practice they will not give this rate to anyone who has any other form of access including cable modem, or any other access to a phone. I've tried discussing this with BT and got nowhere. They seem to think that this is reserving the special rate for true hardship cases; I think it's a monopoly in restraint of trade, designed to make people buy their (crappy) ADSL service instead of much faster cable services.
Unfortunately NTL don't offer a cable phone service, they use BT lines but offer lower per-call rates, which doesn't help me at all.
The obvious answer is to buy a pay as you go mobile and use that instead, and have the BT line disconnected; the snags are first that I don't think that my flat has particularly good cellphone reception, second that I would really prefer not to make people pay a premium to call me, and third that I think I need a land line since once in a blue moon I send a fax.
I'm aware that there are web fax services and I really ought to look into that as part of the answer; for the rest, can anyone point me at a British pay-as-you-go cellphone provider that is reasonably cheap to call to? Are there any alternatives I'm overlooking? I'm vaguely aware of phones that work through the internet but know very little about them, e.g. what connection rate you need, or how you call or receive calls from someone who isn't connected to cable. There seems to be remarkably little information available.