We're registered with the Telephone Preference Service but still a few nuisance calls get through from abroad. They are displayed as international on the phone screen. I answer them and generally it's a recorded message that ends up saying press one for further information. I press one and when a "human" voice speaks I put the phone down alongside the radio and leave it there until they hang up.
I did this on the last nuisance call and could here a woman saying hello, hello are you there. It cheered me up no end.