If you planning to buy a Klipsch S2m headset to use with your N900, my suggestion is don't buy them because they don't work.

For all others who already have bought one, here is my solution to get them to work with your N900.

Hardware solution
  1. Plug in your earbuds. You will hear a strange buzzing noise.
  2. Now very carefully pull them out, not completely only till the noise stops.
  3. Play a song and try to adjust the jack so that the song sounds as it should.
  4. The mic will work too.
Software solution
  1. Plug in your earbuds.
  2. Type alsamixer -c0 in the terminal.
  3. Navigate to the Jack Function control. The value will be TV-Out.
  4. Change it to Headset with the arrow keys.
  5. Go to the Left DAC Mux control, just to the left of the Jack Function control.
  6. Change the value to DAC_L3.

Well as you see both the solution are a pain. But don't get me wrong, the earphones are great. Great sound quality and very comfortable. If you have an Apple device, the earphones will work fine. I have tested them with the iPhone.

Hope that helps.