They have microphones on the earphones itself, sends the signal to a small little thing halfway to the earphone jack, in real time. The recorded sounds are inverted and played back with your music from your mp3/phones/airplane audio.

Sony has mp3 players that has this function, but still require the microphones to be on your earphones. Simple design inference tells you that what's intended to be cancelled is the noise directed towards your ears.

Understand so far?

One customer, came to ask why isn't the microphones on the mp3 player itself, so that you can use any other earphones. It's a million dollar idea, from the first point of view.

But what happens when you put your mp3 player into your pocket? Wouldn't that design be redundant? What does your microphone have to record, and to cancel? The shuffling of your mp3 against your jeans? What the fuck was going through your head? Yeah, sound travels. The full amplitude of the sound may not reach your jeans, thus you don't fully enjoy the noise cancelling that your mp3 is capable of. At this point of time, it's still immature, and thus very likely cannot be done. Even the high end noise cancelling earphones that demand $549 still require the microphones for recording constant, external noise to be on the earphones itself. Why would you want to cancel something that's not directed at your ears. That itself, if inverted, would become noise.

Learn simple engineering much?

Customers who think they know, but don't actually know.