Is it possible to echo what your mic records to the speakers? When I talk on my Blackberry with a headset, it echos what I'm recording back into the headphones. This helps me hear my own voice when I'm talking, so I can regulate my volume.

I'm wondering if it's possible in Mac OS to echo what the mic records back into the speakers and even adjust that volume.

If not, should this be handled at the application layer instead of the OS level?
I would take a look at Rogue Amobea's application LineIn. LineIn is a free app and can be found at http://www.rogueamoeba.com/freebies/.

From Rogue Amobea's site:


  LineIn is a simple application for OS X to enable the soft playthru of audio from input devices. In simpler terms, you can use LineIn to play sound coming in through a microphone or any other device plugged in to your Sound In port, just as was once available with OS 9's "Play input through output device" option.