See the Cisco SPA2102/8000 Manual Reconfiguration Guide.
See the Yealink T4x G & S Series Manual Reconfiguration Procedure Guide.
See the Polycom Manual Flash Procedure Guide.
See the Cisco SPA 500 IP Phone Manual Reconfiguration Guide.
See the Cisco SPA122 Manual Reconfiguration Guide.
This means that the device has both registered and failed to register within the immediate time period. This is an in-between state before the device is declared to have lost registration.