This disclosure presents a modem for use at a terminal for accessing first and second communication networks that comprises a device interface for connecting to a subscriber identity device that stores first and second subscriber identity applications, and first and second pieces of user authentication data, separate from one another, for effecting independent first and second user authentication procedures for the first and second applications, respectively. A processing unit executes the first application to provide access to the first network when the first authentication procedure has been completed, and executes the second application to provide access to the second network when the second authentication procedure has been completed. An actuation component responds to an authentication command received via a host interface to identify at least one of the first and second pieces of user authentication data to perform an authentication task in relation to the identified user authentication data.