The Truecall box we have just sits on the line into the old cordless base station and sends to it's answerphone all calls from numbers that aren't in a list that you program it with.
I'm a trueCall fan, too. Useful product.
I think they may already have one of these, but I will check, thanks for that. I added them to that free service which blocks out cold calls..forget what it's called.
Telephone Preference Service? Worth doing, but may not stop overseas callers or outright fraudsters.