The invention comprises a modem apparatus adapted to provide full messaging and communications interface between a control device and a communications medium such as a telephone line. The modem can comprise an interface adapted to communicate directly with a control system device, such as a programmable logic controller (PLC), using a communications protocol compatible with the normal network communications used in a distributed control system. The apparatus advantageously interfaces directly with unmodified control system devices, providing the ability to send and receive messages from remote devices or personnel via a communications medium. The invention also comprises a control system including a modem device providing full communications between a control device and remote personnel and/or devices. The apparatus can further be operative to monitor certain control conditions via communications with the control device, and to create and transmit messages across a communications medium according to the monitored control conditions.