Call blocking with spoken message? Does anyone know of a call blocker that will let you create a voice message for blocked calls?

What I want is to block calls from hidden numbers. This is almost always salespeople so I want to just block them, but maybe once in a while someone with no ill intent might be calling from a line with a hidden number.

So I want the app to actually take the call, but not tell me about it. Then it should play a sound file that I make and then hang up.

This will let me tell the person at the other end, that I just blocked them to get rid of salespeople and that if they are not such a "person" then they should just use SMS.

I know that some of the apps will let you type in a text that will be sent to blocked callers, but as it will almost never be a cellphone, but an old land line with blocked number, then that will not help a lot.

If no one knows of an app that will let me do this, then I will just have to make it my self, but I thought I'd better ask first.
I found one that does just this last week. Check out http://www.youmail.com. It's an app you download, but can manage it from their website. You can record different greetings for different people; family, business and the main reason I got it.... the number has been disconnected for people I REALLY don't want to talk to! I also have a msg just for Blocked Called IDs, telling them I dont accept them and to unblock their number. And...it's FREE :)