telemarketers and other cranks don't give you telephone numbers so how does this work? you can't exactly ask for their number and expect an answer. until i buy a new phone ( i mentioned that i dropped my phone on it's head ) i don't know who's calling and not everyone has caller id.
also, if legitimate callers know you're blocking, so what? if they're legit, you'll answer. no? i'm so technologically impaired!