Patent ID: 7860082

Claim:
A telephone system comprising: a plurality of terminal devices configured to perform telephone communication via a packet network; and a main unit which accommodates the plurality of terminal devices via the packet network, wherein each of the plurality of terminal devices comprising: an update module configured to update firmware functioning inside the terminal device in accordance with an instruction from the main unit, a storing unit configured to store access information for accessing an ante-unit, to which the terminal device is currently connected, before update of the firmware and to store currently functioning non-updated firmware before update of the firmware, a read module configured to read the access information from the storing unit after update of the firmware if an post-unit to which the terminal device is to be connected under the updated firmware differs from the ante-unit, a recovery module configured to recover a state before update by loading the non-updated firmware from the storage unit if the terminal device is not configured to be connected to the post-unit after update of the firmware, and an access module configured to access the ante-unit by using the read access information and notify the ante-unit of the update result regardless of the success or failure of the update.