I am replacing this headset (It replaced an Explorer 320) with a 510 because I am sick and tired of swivel earhooks getting loose and falling off-which is apparently NOT a warranty issue according to Plantronics. Their recommendation? Replace the headset. I ordered my 510 tonight-can't wait to replace this one. Note-it drops calls frequently, which I know is a cell-phone company issue because it happens with the phone too. But the swivel earpieces are ridiculous. I could have bought a 520 for $2 more but chose not to because of the SWIVEL!