Recently I joined a phone meeting and only after a while I realized the other participants couldn't hear me.
Rather an embarrassing experience...
The laptop's built in microphone works fine, but as soon as I plug in my headset it's muted.
Apparently Windows, or the audio driver, think the device I plugged in has a microphone when it hasn't or vice versa.
The solution is to go to Control Panels, Realtek HD Audio Manager, in the top left corner click the Folder icon next to the analog hole image, and tick the 'Enable auto popup dialog' checkbox.
With this done, when one plugs a headset, windows will ask what type it is and act accordingly.