IT is reported that BT is about to introduce a new service to block nuisance callers. 
There is already a BT telephone which does this excellently, the BT8500. When a call is received the BT Call Guardian comes in and if the caller is on the blocked list it gives two short rings and disconnects the caller. One can set up a blocked list and add to it. There is also an Allowed List which again can be added to. If a call is received from somebody not on either list they are asked to give their name and the intended recipient is asked whether the call should be allowed or blocked.
In the three months since I have had the phone I have not received a single unwanted call, which is the best recommendation possible. An afterthought -- withheld numbers are automatically blocked.
GEOFFREY RICHARDS
Hilperton