also try the "Set as" setting in the bluetooth device list. Comm manager> Menu > Bluetooth. Press and hold on the device listing, you'll get a pop up list.
I have the Plantronics 855, and use it with several different devices. Sometimes the phone (or my desktop's BT dongle) 'forgets' which BT profile it should be using. This always resets it.
If your headset has multi-point connections, you can connect to more than 1 device at a time. ie: I often set my stereo gateway to my desktop and hands free to my phone. Call comes in, my desktop's music auto-pauses while I take the call, then resumes automagically.
Hope that helps.