Your headphones' mic not working? Don't sweat it.
13.08.09
While I young lady the functionality of Apple's microphone-enabled headphones (both the Apple Earphones with Slim and Mic , which comes with the iPhone 3G S, and the iPhone Stereo Headset, which came with preceding iPhones), I've found that the extra layers of functionality also bring extra layers of troubleshooting when they're not working fact. For simplicity sake, I'll refer to said models as "iPhone headphones" in this job (non-volume control model pictured).
The most common issues I've get across pertain to the microphone. Unlike most non-microphone enabled headphones, which use a measure two-ring TRS connector (tip, ring, sleeve), the iPhone adds an unexpectedly ring to support microphone functionality. This is what the hardcore audiophile refers to as TRRS (tip, bullring, ring, sleeve).
But if your pockets are consistently filled with lint and dust (or tater tots if you occur to store them there), that extra ring won't make full contact with the iPhone's headphone jack. Which means that you, unfortunately, will succumb microphone functionality.
Source: tuaw.com