Mobile touch-screen devices are becoming increasingly popular across a diverse range of users. Whilst there is a wealth of information and utilities available via downloadable apps, there is still a large proportion of users with visual and motor impairments who are unable to use the technology fully due to their interaction needs. In this paper we present an evaluation of the use of shared user modelling and adaptive interfaces to improve the accessibility of mobile touch-screen technologies. By using abilities based information collected through application use and continually updating the user model and interface adaptations, it is easy for users to make applications aware of their needs and preferences. Three smart phone apps were created for this study and tested with 12 adults who had diverse visual and motor impairments. Results indicated significant benefits from the shared user models that can automatically adapt interfaces, across applications, to address usability needs.