4 pin 3.5mm audio plug additional equipment usage.

[Jim Ross]

In addition to the many devices already listed for this particular connector there is another one that I haven'[t found on the list.
This is the Hewlett Packard (HP) "Mini" computer (at least the 1000 series).  It is used for the combination mic / headset connector.  The pin connections are probably standard for an audio connector of this type (TRRS or Tip Ring Ring Sleeve) where the tip and the first ring are for left and right audio, the second ring is for the microphone and the sleeve is the ground. 

This computer has an auto sense on the plug which detects whether something is plugged in and disables the onboard speakers and microphone when it detects a connector in this jack.  You can plug a standard 3.5 mm stereo headset plug into this jack and hear stereo audio but the microphone will be disabled. 

I love this site as I've found it very useful but I wasn't able to find this information here so I felt like I should give something back and help improve this site!