When I used my landline, I had an answerphone kind , so that if I was not in it would take a message, but also with my bad back,friends knew to hold on for a little longer as I was probably struggling to get to the phone. If I ever got a call that I considered dodgy, I would simply state "for your information, all my calls are recorded!" With dodgy ones usually they put the phone down quickly. But on one occasion someone purporting to be from Age Concern rang. I knew that this was a scam, and let them waffle on for a while, and then told them the same, then rang our local police and spoke to them and said I had the recording etc., and that it sounded as though they were coming into this area. They were pleased to get the information and a couple of weeks later they did arrest a couple of people, so hopefully I helped a little in that. But it is so sad these days that you always have to answer the phone in quite a brusque manner, until you find it is the hairdresser or your friend ringing at an unusual time.