On a Nexus S, how do I activate the front facing camera in a Fring video call? video calling in Fring is working but the video is only showing the rear-facing camera, how do activate the front-facing camera?
From the Fring for Android user manual, do this after starting a video chat:


  To switch camera, press the switch button on the left side.


If it doesn't work on the Nexus S, it's probably because they haven't had time to fix it since yesterday.  You can report a bug on their forum.