I don't know if Google Voice can do that out-of-the-box, (though it technologically could) but services like Twilio/OpenVBX or Tropo can definitely do that.
I would think that one problem right now is that not many people are really thinking like that yet. So amongst the people who do think about that kind of setups, each solution tends to be pretty specific to their own use.
That's why you have on one hand Google Voice which presents some options around what I would call "programatic telephony" but not fully customizable, and on the other, OpenVBX's kind of solutions which are highly customizable but not trivial to setup for "regular" people.
But yeah, it's now trivial to do and I'm sure it'll come with time.
I would think that one problem right now is that not many people are really thinking like that yet. So amongst the people who do think about that kind of setups, each solution tends to be pretty specific to their own use.
That's why you have on one hand Google Voice which presents some options around what I would call "programatic telephony" but not fully customizable, and on the other, OpenVBX's kind of solutions which are highly customizable but not trivial to setup for "regular" people.
But yeah, it's now trivial to do and I'm sure it'll come with time.