Mitel Compatible Plantronics EncorePro 520 HW520 Headsets Bundle for Mitel 50xx 51xx 52xx 53xx 55xx 85xx 8600 Bundle of 2 items - Plantronics EncorePro 520 Headset and Mitel compatible telephone interface cable Compatible with Mitel 50xx 51xx 52xx 53xx 55xx 85xx 8600 Ultra Noise-Canceling microphone filters out background sound