Infoman, Sadly it doesn't work like that the vast majority of these calls are taped messages. The message is triggered to start as soon as they hear a voice on the number dialled and runs through to the end and then the line clicks off their end and they go on to the next call.
Far simpler, if you get a call and do not recognise the number, is to pick the phone up and say nothing. If it is a scam after 5 seconds or so, listen carefully, and you will hear a little click as the machine the other end clicks off because it is programmed to respond to the human voice. No voice, no message.
If it is a genuine call, during those five seconds the caller will say something, In my case I then explain my silence and we get on with the call.
As a result I have no idea which scammers are trying to contact me because I never hear their message.