Disable Phone's Built-in Microphone? I just conducted a tiny experiment with the original headset that comes with Nexus One: I plugged it into the phone, expecting the phone built-in microphones to be switched off, replaced by the microphone on the headset.

I was disappointed to see that the voice input behavior of the system didn't change: The phone seems to continue picking up sound from the built-in microphone(s).

So, I thoroughly covered the headset's microphone with tape and tried again...

Still, no change. The Nexus One's built-in microphone are fully enabled.

This is disappointing because I really need to disable the Nexus One's built-in mics, so that I can use a different microphone instead.

Is there a way to accomplish that?
Maybe disabling the noise cancellation feature might work..

Get a rooted file editor first, then
from "/system/build.prop" change the 
"media.a1026.enableA1026=1" to "media.a1026.enableA1026=0" 

Then do a reboot. See if your problem is solved. I simply suspect the android's mic always gets enabled for the purpose of noise cancellation during calls/voice input.

REMEMBER! I do not hold responsiblilty for any failure. I suggest you make a backup and everything when you try this.

SOURCE: http://forum.xda-developers.com/showthread.php?p=6787214