To provide a data communications system which makes it possible to know the operation status of equipment without going to the installation location of the equipment. A management apparatus for notifying a center about the operation status of equipment has an operation status identification management table containing identification numbers which uniquely associate each piece of equipment with its operation statuses. When the management apparatus is notified of the operation status of equipment, it sends a user device such as a user-owned wireless mobile terminal the identification number which corresponds to the reported operation status, from among the registered identification numbers, as calling number information in a call-in message. The user device, which registers calling numbers and operation statuses of equipment to be displayed in advance using a telephone directory function, displays a message indicating the operation status of equipment which corresponds to the calling number contained in the call-in message.