This study analyzed driving performance while using different mobile devices in different road configurations and geometries during a critical driving situation. Three different road environments were implemented in a driving simulator: an urban road, a two-lane rural road, and a highway. Thirty drivers with an average age of 26.8 years were asked to answer a phone call while driving, using different mobile devices: hand-held, hands-free, and hands-free voice-activated cellular phone. The effects of using the mobile phones were also compared to the BC (no phone conversation). Driving performance, under car-following conditions, were collected and statistically analyzed when a sudden braking of the leading vehicle occurred. The main results demonstrated that the driver's speed generally reduced during the phone call whereas the reaction time generally increased, especially under certain driving conditions (urban road, along tangent, using hand-held mobile device). This study analyzed the effects of using a mobile phone while driving, highlighted the worst combinations of the variables investigated, and demonstrated that some reductions in driving performance were revealed, especially in the urban environment, even when using mobile equipment permitted by the regulations of several countries.