Headset Buddy: PC Dual 3.5mm Headset to RJ9/RJ10/RJ22 Phone Adapter (PC35-RJ9A) Use PC Headset with most VOIP phones that have a RJ9/RJ10/RJ22 headset jack Save money by buying PC headsets to use with your office phone's headset jack Not for handset jack. Does not work with RJ11 jack, which is wider than your headset jack (6 positions vs. 4). RJ11 jack is what is in the wall. RJ9, RJ10, RJ22 are what is on your phone handset or headset. Works with mono and stereo PC headsets Convert two 3.5mm plugs to single 4P4C RJ9/RJ10 headset plug