Someone asked me about this a while ago, can't remember nor find his name or email.

Just to confirm, are you talking about this?: http://en.wikipedia.org/wiki/Automatic_message_accounting

I don't think there is a stack or code to handle that in the open source community (though, you never know what is out there). From what I see requires MF tones, which at least spandsp is able to generate and detect. Some logic is required on top to interpret and respond to the tones accordingly.