He says he has talked with Apple via both email and phone.
hmm yeah but i wonder what they had to say about it
My guess is: "Yes, we know about it, we had an engineer spending X amount of hours actually implementing this feature".
I guess I misunderstood - I thought he was saying he tried to contact them but they didn't reciprocate.
It isn't really an issue they can fix. Voicemail and missed call notifications come in from carriers over specially formatted messages. You'd need to develop a new out of band messaging protocol that is as reliable as SMS delivery and get all the 30+ carriers Apple works with globally to roll it out before they could turn off the old stuff.
Why does it have to be out of band? Couldn't they just append a signature or something?