2.5 mm Headset Cord for Plantronics QD Compatible Headsets
Plantronics M210C Headset for Cordless and Mobile Phones with 2.5mm Connection - PLNM210C - Shoplet.com
Amazon.com: 2.5mm Jack to QD Bottom Adapter Cable - Plantronics Alternative to fit Phones with 2.5mm Headset Connection for Cisco SPA303,501G,502G 504G,508G,Cisco Linksys SPA921 922,etc : Electronics