I'm also interrested in this, after my ongoing project this will be my new one.
I think it should be possible.
I mean, what do we need.
1. Detect microphone level, think I've seen this in the forum.
2. Record sound, tried that.
3. Play the sound, done that.
I guess the detection of sound level and trigger the recorder is the tricky part.
Anyone done something similar that can get us started?