How to increase the microphone volume?

I have already gone through http://www.modaco.com/forums/topic/3...gain-settings/ and http://www.modaco.com/forums/topic/3...es-in-omnia-2/ . There they explains about auto gain control. It was all a head ache. What I want is simple. When I connect my "headphone" (no headset), I use to talk using my phone's inbuilt mic. But my voice becomes feeble comparing to the normal talk without headphones. The other persons are able to listen to my voice in less clarity compared to normal talk. I want to increase volume of mic (not speaker) when I connect headphone and talk. There is no problem with the speaker volume. Auto gain control setting is not there in the settings, and is accessed through code *#0002*28346#. How can I increase my mic volume alone?

Thanks in advance :)