This is a JNS Technologies MOT-BMW0203 handsfree integration harness for use with select BMW vehicles.  This harness utilizes a telephone audio input on the vehicle's headunit itself, that is triggered to swtich over to the handsfree audio of the carkit when requested.

Some of the compatible vehicles include:

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• 3 Series / 02-04
  5 Series / 02-03
  X Series / 02-04
   
• On activation of the Mute line, the audio will switchover to the handsfree kit.
  
  You can also use this harness to integrate audio into your car stereo from other mono sources by triggering the mute enable line (navigation units, radar detectors, CB radios, etc.).  A carkit-specific adapter harness may be required for your installation, or you can wire the connections directly.

Thanks for looking!