Your question is awesome and made me want to find out. To test, I made a Duo call to my wife using my laptop. I thought disabling my laptop's mic would cause no sound to be transmitted, so I kept it active and walked 30 feet away from my computer into another room. I could hear my wife fine, but she could not hear me. So, in this test, I can conclude the mic on these earbuds do not work while there is an active Bluetooth connection with the charging case.