Unplug the Ethernet cord and power adapter if you are not using Power over Ethernet (PoE).
Keep holding the "#" key down until the phone displays the "Rescue Mode" message. This will give you a menu with several options.
Press 1 to select the first menu option, as this will clear any configuration data and restart the phone.
That's it! Your phone is now ready to configure with your preferred VoIP solution.