I have horrendous issues with this phone and several headsets. My plantronics Voyager 520 randomly disconnects and most of the time I can hear the caller but they can't hear me. The only way to get it reconnected is to reboot the handset. I tried a cheaper plantronics explorer 360 which exhibited the same issues.
My E71 had similar issues with the 520, but nowhere near as bad as this. I then tried a Motorola H12 which seems to maintain a steady connection to the handset but has horrible sound quality (loud as hell and cuts in and out constantly).