This method of resetting the phone also causes it to revert to its previous version of firmware if it has been upgraded.
Disconnect the power supply cable. This is the same as the network cable as the phone uses power over Ethernet.
Insert the PoE cable into the network connection socket.
Repeatedly tap the mute button on the touch screen.
When the LED's turn red, press the volume up button once.
Result
The phone reboots to its default settings.
The phone also reverts to any previous firmware it has if any. Therefore, if required, upgrade the phone firmware. See Manually upgrading the B199 firmware.
