How do I switch an active call from the Nokia Bluetooth Headset to the paired phone without losing the call?

To switch the call from the headset to the paired compatible phone, press and hold the power key for about 2 to 3 seconds  (the headset switches off), or use the respective function in your phone. To switch the call back to the headset, switch on the headset, or press and hold the answer/end key (when the headset is on).