In a unified communications system, communications media refers to the actual method by which communication takes place. A key example is a software-based phone that uses Voice over Internet Protocol (VoIP), which allows users to make phone calls through the internet instead of relying on traditional analog systems.
Option B: Incorrect-mobile conferencing devices are tools, not the core communications media.
Option C: Incorrect-signal converters are hardware for compatibility, not communications media.
Option D: Incorrect-traditional phones are legacy hardware, not unified digital media.
Thus, communications media in UC systems is represented by a software-based phone using VoIP.
Reference:
WGU Information Technology Management - Unified Communication Tools, section on VoIP and Communication Media.