According to B-SIG, all Bluetooth headsets and headphones must be backwards compatible with version #1, and #2 units, as is the current version #3. Version #4 will be out later this year, and although the consortium says it will be backward compatible, we'll have to wait and see.
One other thing. I use Bluetooth headphones I purchased from Overstock.com, along with a stereo dongle. Both work very well together.