Amplifier Cable, Adapts M12/M22, MX10, SP, PLX to NEC or equivalent telephone systems. Previous Part# 40287-05 (stamped as 88566-05 on the cable)
Also used as an extension cable to connect the APC-4 (APC-43) control connection into the Cisco expansion module 7914/7915/7916. It extends the Plantronics APC-43 audio input to reach the headset jack on the phone.
When using a Polycom IP phone sidecar and the Plantronics APP-51 EHS. You require 85638-01 extension cable so the APP-51 cable can reach sidecar.