asterisk users - Sep 2005 - monitoring VM via speaker and grabbing connection

This is an old problem, but I have been unable to locate a solution so 
far  :-(

I want to set-up asterisk so that it mimics a typical answerphone ie.

someone calls in - you call screen in case it's:-

a) a telemarketer
b) someone else you don't won't to talk to
c) someone you don't want to talk to because you are busy

So you listen as they record their message, and if it's important, you 
pick-up, which stops the recording.

How can you do this, in asterisk ?

Regards...Martin