There are a vast number of research and studies undertaken within the domain of user-centered design concerning the design process of an artifact, but still there are questions being raised of the relatively new and successful field of mobile design. During recent years mobile technology have surpassed the standardized thoughts of how to prototype and evaluate such a ubiquitous device. The paper addresses this predicament by discussing aspects of fidelity differences in an early design process of a mobile design. The example being presented refers to a design study of an iPhone-application, where two different types of prototypes were created and user tested, a low-fidelity paper prototype and a mixed-fidelity interactive prototype. The paper sets focus on the various differences between these fidelities closely related to the case. It also reflects on how mobile design approaches can mature during the early stages of a design process.