I just got a Plantronics Voyager 855 which is a nice headset that can be a normal mono earpiece but has a second earphone you can plug into it to make it stereo. It supports A2DP and is really small and light. It works great with my phone and my N810.

It cannot, however, be actively connected to both at the same time. If both it and BT on either my phone or N810 are on and it isn't actively connected, pushing its button connects it. If the headset and both other devices are on, doing that will only ever connect it to whichever one it connected to last.

Unfortunately, it doesn't seem to be possible to get around that; it sacrifices the Voyager 815's (which looks just like it) ability to connect to two for A2DP.

Still, I use VOIP and my phone very differently, and really have no need to be able to interchange between the two rapidly.