Turn off display when using phone?

[ppc_user101]

Sorry if this is already out there somewhere, but I did search for "display off when using phone" and a few variations of that and found nothing useful.

All I'd like to do (in the interest of power conservation) is be able to turn off the display (or have it turn off at the usual timeout when the device is idle) when I'm using the phone. One of the nice things about my old Blackberry was it's battery life...the display automatically shut down when holstered even when phone was in use. For my Sprint HTC Touch, I'd like to be able to turn the display off just like you can when you're using Media Player and keep it going.

Is there a setting I'm not finding or is this deeper, like a registry edit? I'd rather not install addiational apps to be able to turn it off...I'd like to keep it as simple as possible, like finding the right setting or a simple reg edit.

Thanks!