Just had this occur with a VOIP call. Apparently the headset locked up shortly into the call, I tried switching to the handset but the audio stack was AWOL and I got nothing so I hung up. After that I went to start up some tunes again and the headset was still locked up so the music came out the N900 speakers. I didn't recall the reset shortcut so I put my headset on the charger for a while thinking it might have been a battery issue as I've been using it off and on for 3-4 days since I first got them and fully charged them up. Charging didn't fix the issue, but finding the shortcut here and resetting fixed the issue, and I haven't run into it again yet, but I have not been using the device as a phone yet, simply an NIT/VoIP device.