title: Need a list of WURFL ids of mobile devices sorted by OS. not using "device_os=" of WURFL
body: <p>I need to create groups of all mobile devices for each OS.
  I want to use the WURFL IDs, and I'm aware that WURFL sometimes specify the device's OS using "device_os=". Unfortunately many mobile devices are missing this property so I can't rely on it.
  Is there another way? </p>