It is not exactly the solution you look for but on iOS you can use call blocking apps which work in a similar fashion to the safari blocking extensions. They pr

It is not exactly the solution you look for but on iOS you can use call blocking apps which work in a similar fashion to the safari blocking extensions. They provide a list of blacklisted numbers to the phone app and they can either tag them (say, as a telemarketer) or block them outright. I currently use Callblock and it works fine. One advantage of this system is that the blocking provider does not need (and can't have) access to your phone call history at all. The disadvantage is that it is a blacklist only, you can't invert the rules. As a side note, although I would _love_ to just ignore all calls from numbers I do not know, at least in France most companies such as banks, taxman and so on will call you from a withheld number and they don't always leave a message.