This product is either discontinued or we cannot get that from suppliers.
Poly/Plantronics 28959-01 S Cable Qd To Dual 3.5mm Plugs, Black, Connector on First End Quick Disconnect Male, Second End 2 x 1/8" (3.5 mm) Mini-phone Male, Cable Length 10 ft, Headset Compatibility Plantronics H-series and P-series corded headsets.
The Plantronics Quick Disconnect to Dual 3.5mm Cable allows you to connect H-series and P-series corded headsets to your computer.