Available bandwidth is still a limiting factor for mobile communication applications. Multisensory communication has already been identified as an possibility to moderate this limitation. One of the strengths of mobile communication lies in its combination of visual and auditory modalities. However, one of the most salient features of mobile devices have are their small screen size. This paper explores how the potential for multimodal synergy relates to the small screen size. In an experiment with 54 participants, the intelligibility was tested using a standardized video-listening test. The videos had a signal-to-noise ratio of -9dB and were presented on three different screen sizes, whilst keeping the video and auditory signals equal. Intelligibility was found to be significantly higher when using a large screen in comparison to using either of both smaller screens. We conclude that multisensory synergy is key to mobile applications, yet that screen size is a substantial constraint to this synergy. We argue that knowledge about human sensory processing can alleviate this constraint and maximize the potential quality of service of mobile video technology.