Abstract: An apparatus and method for a data communications device to selectively operate in a plurality of analog and digital modes, including as an analog modem, as a digital modem, and as a terminal adapter. The embodiments provide for a single, integrated data communications device to be configured and also subsequently reconfigured to provide for data communications over a variety of networks, including public switched telephone networks, leased line, and digital networks, including T1, E1 and ISDN. The various embodiments further provide for the selection of a primary digital operating mode while simultaneously providing for automatic reconfiguration for an auxiliary or back-up analog operating mode. The various embodiments also provide for signal simulation of the various networks, such that the actual coupled network is transparent to a data terminal transferring information through the data communication device to the network.