What we need is a audible CAPTCHA type system
My suggestion, allows callers to get through - if they get the number right (using an audible CAPTCHA type of system (asking "rotating" simple maths questions - what is 2+5 for example - input 7 on keypad for access) - this will effectively block automated call machines (which, in my experience, make up the vast majority of nuisance calls) - the caller can then be added to the list of "welcomed" callers by dialling a number after the call is closed (or on line) if they get the answer wrong - or choose not to respnd to it - our phones DO NOT RING !!
I understand that BT's offers an option that blocks ALL calls if they are not on the list - this takes it too far - what about genuine emergency calls ?
My system is better - it would then allow unrecognised, but genuine, callers - a way through security - you can then decide whether to allow them a permanent pass or not
and, most importantly - fake numbers would be blocked !!
Simple - please implement as soon as possible