Plantronics 18709-01 (PJ327) 2-Prong to Modular Adapter

Plantronics 18709-01, also called the PJ327, modular adapter allows wireless headsets to be used on 2-prong ports.  You can also use a modular corded amplifier with the Plantronics 18709-01 when plugging into plug prong ports.  

Plug Prong Adapter - For use with wireless headsets and modular amplifiers