Are you talking like a "ear piece/microphone" combo unit designed to make calls with, or a stereo headset that uses the A2DP protocol? (A2DP is the protocol used for full stereo bluetooth - It's a "one way" protocol, that gives a high-quality high-bitrate stereo sound into stereo headphones)
The phone will treat the normal "ear piece" protocol differently than the A2DP protocol, as to which types of audio it will send over the non-A2DP device.
You need an audio gateway/router application to redirect the audio to your BT device if it is not A2DP. Otherwise, as mentioned above. It won't work on a normal Ear Piece. They do have an app in the market, but it isn't free. only a few bucks. FYI: A2DP is best audio option, if you do a lot of listening through BT device. Get a real A2DP BT device.