Chapter 6: User Interfaces for Mobile Media 277 After the call ends, the music resumes. Now Cathy stops it, however, as she feels it is better to converse with the old fellow. He apologises for overhearing the conversation and butting in. Cathy does not mind, especially after getting useful help with her phone. Besides, she loves talking to people. Beats music any time. Well, except for Weather Report, but now she can get back there when she wants. The previous illustration seems common and perhaps even reasonable, but it also consists of a few interesting cases related to system behav- iour. First, how is the incoming call presented in the fi rst place? Typi- cally, a ring tone is used to alert the user, in addition to haptic and visual output, but now the user is already using the audio channel and the device is placed in the bag so the vibration patterns and visual indicators are not noticed. Second, answering the call will pause the playback as they both use the same modality. Of course, the system could continue playback on the background of conversation, but that is not desirable as it hinders the conversation. Next, the user needs to access the calendar while being engaged in a call. Therefore, the inter- action with the device should not affect the call. Furthermore, when the phone call ends, what is the state to which the system should return? Before the call, the music was being played, but on the other hand, the calendar application is open since the user interacted with it during the call. Design decisions such as these are task-dependent and must be made on a case-by-case basis. 6.6 The Effect of Device Category on UI In Chapter 2 we classifi ed mobile devices into three categories based on the number and expandability of their functionality. Evidently, these factors have an infl uence on the user interface too. In fact, the category of the device affects the UI greatly as the increased number of features require more fl exibility from the UI (remember the feature race discus- sion at the beginning of this chapter?). For example, if the device is only dedicated to audio playback, the UI should refl ect this aspect and provide fast and easy access to the core operations related to this task. On the other hand, the UI of a toolbox device should be fl exible enough to support a wide range of different tasks. To make things even more interesting, all possible tasks for a toolbox device are not even known at the time of the device design (since the platform is open for further (third party) application development). The user interface of dedicated media devices is normally minimal; only the controls for the most frequent actions involved in primary