I am having mixed results using my Optimus V with a Bluetooth earpiece (for telephone communications.) I have several older bluetooth units, and each pairs correctly. I can talk and hear other party with no problem. The issue is with the voice prompts from the phone: they are very weak and nearly impossible to hear. (no problem with the phone conversation, though.) Is there a way to increase the level of the voice prompts to the same level as the phone conversations?
So if you check the volume levels in the phone settings, is Media adequately turned up? Is the notification volume also up? I'm not sure if it's either of these, but from your description I would imagine it's just an awkward volume setting instead of an actual problem with the hardware or a headset.