We bought some BT phones with this call guardian thingy in. If the caller isn’t in your list of allowed callers, they have to jump through hoops to talk to you, they have to press 1 or something, then record who they are, this is all before your phone even rings, then your phone rings telling you you have an announced call, you hear them say who they are & you can choose to answer, put them straight through to answer phone, or reject their call.
nobody even bothers going through the process as they know that you won’t take the call anyway, so if the phone ever rings, I know it’s someone I will want to talk to.