My mother-in-law will definitely accept calls from scammers even if they announce they are scammers so this process is useless! We just want something that ONLY allows trusted callers on pre programmed numbers to come through to her. Having spent hours searching we are not sure this facility exists. If not, someone needs to invent it urgently
You can change the Call Guardian mode to Answerphone instead of announce, then turn the answerphone off, on the base unit. I think callers are told a message cannot be left. The phone will only ring for numbers stored in the phone.
The "do not disturb" option should also stop calls, apart from those on the VIP list within the phone.