When you open up Skype's "Sound Devices" under "Options", it suggests to change sound settings by using your Desktop Manager volume control. How to choose between the default front/rear audio and your webcam or USB headset is not readily apparent there. If you click on the "Recording" tab you will notice nothing is shown. While having this tab open start a call to Skype Testing Service (or start a normal call). When it is time for you to talk/record the Recording tab will now display a window with the current default device shown. Click on that pane and from the drop-down change the default device to your preferred mic. It will be persistent until you go back into the "Recording" tab and change to another device. Just remember the recording device must be in use before you can change it and you will have to arrange the two windows so you can get at the drop-down pane to make the change.