How to use the front camera with Tango?
The Recent Changes list for v1.4.4857 (released around 11/11/10) states:


  
  We added support for front facing cameras on Samsung devices
  We fixed an issue that was causing some HTC EVOs to reboot when launching
  Tango
  


So it looks like they needed to change something specific in their software to let you use the front facing camera, and they've done that now!