I use a Bluetooth, and plugged in microphone all the time - so there is audio input. Have you possibly tried it with a know good headset? Let me put it this way - if you can plug your headset / audio into a standard Samsung Galaxy S4-S7 audio input, it works on the Surface Pro 4. I use it all the time to talk to my family back home as I am stationed in Germany. I would, if you have not already solved this, attempt to plug in a known good microphone / headset solution and see if you get positive results. Another thing you might want to try is go to the small picture of the speaker on the bottom right tray and "right click" - then left click on "playback devices" and set your headset / whatever your using to the "default communication device" - See if that helps you. Good Luck! Merry Christmas.
