I mean the simple analog headset pluggable into the jack of a phone. Not USB, not bluetooth, not fancy proprietary plugs with extra connectors – just a generic stereo+mic jack.
The four "bands" on the jack plug are GND, right earphone, left earphone and microphone. And there's nothing to cover the buttons – usually "Volume up/down" + "Media key" for receiving the call.
How do these buttons communicate being pressed to the phone?