Plantronics EHS Cable APP-51 38439-11 Polycom for CS500 + Savi - Electronic Hook Switches EHS communicate electronically with your phone giving your wireless headset answer/end and ring alerts remotely. The use of an EHS cable eliminates the need for an HL10 handset lifter. (Formerly 38439-01 - APP-50). Compatible with: CS500 Series (CS510, CS520, CS540), Savi Office (WO100, WO200, WO300, WO350), Savi 700 Series (W710, W720, W730, W730M, W740, W740M, W745) Plantronics