This product is either discontinued or we cannot get that from suppliers.
Poly Plantronics Cable Modular Adapter 85638-01, Extender For Apc-42 Apc-41 Apc, Conductor Copper.
Use Plantronics 85638-01 (formerly 40287-05) adapter to extend the APC-4/APC-40/APC-41 audio input to reach the headset jack on the phone.