Bluetooth Headset to Bluetooth Transceiver
It really depends on the bluetooth device you plan on using with the arduino, both on the arudino end and the headset itself.  You would have to make sure both sides support the same protocol (Example: SSP).  However, even so the Arduino software implementation of BT only supports SPP (serial) rather than HFP (hands free) which is used on bluetooth headsets. 

You would need one of the new A2DP sterio headsets which ARE supported by the arduino software and many modems.   In short, you would need both a headset and arduino BT module that support A2DP to get this to work.  However, I have no idea how you hope to process sterio audio on an arduino.  Good luck.