I second this emotion! I get probably at least 5 unwanted telesales calls a day, and it's a real pain.
BTW, I did have this feature with AT&T. Bought a bundle package that included call waiting, forwarding, etc. and allowed two cool kinds of blocking. One blocked a number entirely and the other asked the caller to say their name, then rang through and asked me if i wanted to accept the call. I'd be happy with just the former capability.
With AT&T, I could hang up and then dial some code to tell AT&T to block the last number I received a call from. Very handy!
Thanks -- Barbara