Users experienced call quality issues when calls are answered using a headset.
- Sennheiser DW BS ML headsets
- Poly VVX 600
Disable Echo Cancellation.
The issue was caused by the Echo Cancelation option being enabled, which is not required with Sennheiser headsets. In this case, the 8x8 Phone System configuration included Sennheiser DW BS ML headsets plugged into Poly VVX 600 physical phones.