Abstract: In a telephone system employing a PBX server to communicate with local telephones over a local area network, fallback adapters are provided to automatically respond to a power failure and also respond to the failure of the PBX server to automatically connect the telephones directly to a telephone line. This automatic connection enables the telephones to be used as analog phones and make and receive calls directly without using the PBX server. Power failure is detected by relays which default to a position to connect the telephones directly to the telephone line. The fallback detectors have controller logic which detects the presence of a ringing signal on the telephone line and the failure of the PBX to respond to the ringing signal. In addition, the fallback detectors detect the failure of the PBX to respond when a telephone is used to attempt to make an outgoing call or a call to another one of the local telephones.