We have a BT Guardian phone. You programme it with the numbers you wish to receive calls from, family, friends, doctor, etc. If a different number calls they are asked for their identity and then the phone advises you that you have a call and you can either answer or decline. We haven't had nusience calls for the last three years!
SPELL CASTER[+2781-8744558]]╬WALIVIS BAY, HUAMBO, NDOLA, NAMPULA, ARUSHA, MAUN, OSHAKATI, LOBITO