just a correction - I didn't find them - they have been posted here before, I just remembered them
Check your backlight timeouts, your phone backlight should turn off during a call within whatever time you have set for it.... if the backlight is staying on the whole time, you'll be drawing an extra 100ma or more depending on how bright you like your backlight.
Hmmm... I just called myself from my home phone. Normally, you'd not be looking at your screen while talking - in the call, the backlight stayed on for well over a minute. I wonder if its not blanking during a call ever?
Here's something you can do if you really do want to save some juice. Download and install
http://www.vijay555.com/?Releases:VJEschaton - map the displayoff link to a hard button (I use the ie button) - then you can just hit that hard button while you're in a call, and hey presto your screen is off. Not just the backlight, but the whole screen. Hit the power button to bring the screen back on.