I know a few owners and they use quite a few makes of headsets. I can guess that some airhead vendors will claim only theirs work.
Just one note, the pairing can be a pain and the version of firmware in the 650 could disable bluetooth so make sure your firmware has bluetooth enabled.
I am looking for a bluetooth headset. can you tell me why I can or can't use a universal type headset. I am look at the BT250v or the new BT500 both from Jabra.