This paper presents a new concept of an approach to evaluate the assurance of the audio quality and its impact on the security of mobile phones used as multimodal user guides at the same time. Differently caused interferences can influence the subjectively perceived audio signal. Finding objective measure values acts as the motivation for the development of the presented model. This model to evaluate audio codecs in relation to three defined and interdependent challenges, addressing three different kinds of problems -- technical, environmental, and security, will be introduced while its evaluation is in progress. As a result, our model, which is still work in process, will help to provide recommendations to future developments and to establish standardizations in the field of multimodal user guides.