I have tried 3 different headsets with the last being the Plantronics 665 which is a newer version than the voyager 510.  I use the 510 with a Blackberry 8820 and so far it has worked flawlessly and I've been using it for about 1 week.  The sound is clear and loud and the background noise that other people hear is very minimal, even when driving with the windows down.  On my other headsets, when talking to other people, they all said that it sounded like I was talking through a tunnel, but on this headset, the Voyager 510, I've had everyone say that they couldn't tell I was talking via Bluetooth.  This headset may be a little bigger than some of the newer models that are out now, but once you put it on, it is very comfortable and you can't tell the size.