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4 pin 3.5mm (2.5mm) plug connector layout
4 pin 3.5mm (2.5mm) plug connector
iPhone headphone (handsfree)
Pin
Number
Pin
Name
Description
1 Tip Left audio
2 Ring Right audio
3 Ring Common/Ground
4 Sleeve  Microphone

Pressing the headset button shorts Microphone to Ground

Inserting a 3-pin plug into the iPhone's 4-pin receptacle would also short Mic to Common and the L/R earphones will work correctly.

Using 4-pin Headsets provided by certain Phone Carriers also work with the microphone connection and certain remote functions.

Using iPod Earphone that use a microphone with a Cell phone may not provide the mic connection, and wil likely use the phone's internal mic instead.

The iPhone requires a certain impedance on the microphone pin for the input to be detected and used.  1600ohms is a good choice as it is very close to the mic on the standard Apple headphones.  So, if you are running an output from a PC or other amplified device into the iPhone mic input you will need to put a 1.6kohm resistor in series for it to work.  Tested on iPhone 3GS.

According to 33 reports in our database (23 positive and 7 negative) the iPod Nano (4th, 5th Gen), iPhone (1st, 2nd, 3rd, 4th Gen), iPod Shuffle (3rd Gen), Cell Phone Connection pinout should be correct.

Is this pinout
iPod Nano (4th, 5th Gen), iPhone (1st, 2nd, 3rd, 4th Gen), iPod Shuffle (3rd Gen), Cell Phone Connection visual pinout:click to enlarge
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