I like the idea of moving as much decision making as possible to the phone, but I don't want a whitelist. That would require me to make the effort to whitelist people, plus having the prescient power of anticipating which strangers I want to hear from (e.g. whoever found my dog and called the number on her collar). I'm ok with getting a call from a stranger, as long as their "return address" isn't forged. If the return address is correct, and they are annoying, I can blacklist 'em. Allowing strangers to call me is the best default. Not perfect (it's easy to imagine some failure scenarios), but best.