Sorry hristov. I meant to upmod but my giant thumb hit the down arrow on my mobile by mistake. Unfortunately there is no way to undo my erroneous vote.

It's one of those head-smacking why-didn't-anyone-think-of-this-before kinda ideas.

It's a fairly common feature, for example there are several bluetooth headsets on the market with dual mics for noise reduction.

But zero actual phones, until this one.

See here: http://en.wikipedia.org/wiki/Active_noise_control

The basic idea of dual microphones to filter background from signal is pretty common.

Cost ($0.50 over 10 million phones adds up) and CPU/DSP power to perform the cancellation.

The cost of the second microphone can be substantial. The cost of the CPU power may not be. You can get a very long way in noise cancellation simply by placing the two mics near each other and subtracting the signal of one from the other. See the noise-canceling entry of http://en.wikipedia.org/wiki/Microphone#Application-specific... (the last paragraph in the "Application-specific designs).

You don't even need a CPU for that, you can do that with simple electronics. Noise-canceling headphones are freakishly complicated, directional (what is often meant by "noise canceling") microphones are possible with very simple designs.

I wish I could google up a piece on signal processing but my google search is getting dominated by things I can buy.

Did you try "Show Options" on the results bar? Then choose "Fewer shopping sites." Worth a shot.

I hope this could also be used when filming to have the mic directed at the target instead of the person holding the phone.