[Asterisk-biz] answering machine detection

[Preston Garrison]

Has anyone worked on any code or have any experience doing answering 
machine detection.  Someone I was talking to was telling me something 
like normal callers do more mhz? :)  Which I assume maybe they mean 
that a normal caller sends higher frequencies since its not 
pre-recorded.  However I am wonder if the codec compression would 
remove that.  Anyone out there have any experience with coding such 
things or using them?