Implementing Voluntary Travel Behavioral Change (VTBC) programs aimed at encouraging sustainable mobility faces three key challenges: biased samples resulting from self-selected participants, reliance on one-time surveys instead of panel data to track behavioral changes, and limited use of econometric models. Recent research suggests that GPS-based panel data can provide more accurate evaluations. This study evaluates a smartphone-based VTBC program designed to encourage behavioral change among drivers in the metropolitan area of Cagliari. The VTBC program was implemented through Personalized Travel Plans (PTPs), which suggested alternatives to car travel, and included gamification elements. Different econometric models were constructed to assess the program’s effects. A joint binary-ordered logit model was used to simultaneously estimate the probability of participating in the program and the likelihood of making sustainable tours after receiving a PTP and engaging with gamification. Additionally, a multinomial logit model was developed to analyze tour mode choice probabilities before and after the intervention. The model results indicate that receiving the intervention reduces the probability of car use. Furthermore, in addition to the intervention itself, factors such as car ownership and psychological variables significantly influence both the likelihood of participating in the program and the adoption of more sustainable travel behaviors.