Its just an inductive pickup. In most phones some of your voice is fed back into the earpiece, this is called sidetone and is used to make you self regulate th

Its just an inductive pickup. In most phones some of your voice is fed back into the earpiece, this is called sidetone and is used to make you self regulate the volume of your voice. https://en.wikipedia.org/wiki/Sidetone https://en.wikipedia.org/wiki/Sidetone