If all of a sudden your iPhone headset stops working and every logical attempt of fixing it fails then (as weird as it may seem) the problem might be a chunk of innocent looking "lint!"No, I am not kidding!
My headset was giving me headaches, I tried hell lotta things before I found this blog and this thread. Do whatever they say and it might magically start working again.
If it doesn't then the Apple Support lines are open 24/7 :)

