Electronic hook switch cable is designed for remote desk phone This cable eliminates the need for a HL10 handset lifter. Only compatible with Plantronics CS510, CS520, CS530, CS540, MDA200, Savi W710, Savi W720, Savi W730, Savi W740, Savi W745, WO100, WO101, WO200, WO201, WO300/50. Works With Following Polycom Phone Systems: SoundPoint IP 320, SoundPoint IP 321, SoundPoint IP 330, SoundPoint IP 331, SoundPoint IP 335, SoundPoint IP 430, SoundPoint IP 450, SoundPoint IP 550, SoundPoint IP 560, SoundPoint IP 650, SoundPoint IP 670, VVX 300, VVX 310, VVX 400, VVX 410