Viruses that infect smartphones are emerging as a new front in the fight against computer viruses. In this paper, we model the propagation of mobile phone viruses in order to study their impact on the dependability of mobile phones. We propose response mechanisms and use the models to obtain insight on the effectiveness of these virus mitigation techniques. In particular, we consider the effects of multimedia messaging system (MMS) viruses that spread by sending infected messages to other phones. The virus model is implemented using the Möbius software tool and is highly parameterized, enabling representation of a wide range of potential MMS virus behavior. Using the model, we present the results of four illustrative MMS virus scenarios simulated with and without response mechanisms. By measuring the propagation rate and the extent of virus penetration in the simulation phone population, we quantitatively compare the effectiveness of mobile phone virus response mechanisms.