Urban Air Mobility offers today interesting characteristics to disrupt the transportation industry and to become one its driving forces. In this report, we examine and compare the potential market size of a commuting service operated by electric vertical takeoff and landing (eVTOL) aircrafts in the 40 largest US Combined Statistical Areas (CSA), all considered as potential candidates. We first develop a discrete choice model based on a stated preferences survey to understand demand drivers between car, autonomous vehicle and eVTOL. We then apply this model on a dataset that contains commuting origin-destination pairs for each of the 40 cities, derived from cell phone GPS location data and provided by a major US phone carrier. By aggregating probability and expected number of commuters on each pair, we derive market size estimates and ranking to understand which locations are the most beneficial. Sensitivity analysis to the assumptions used in the methodology and scenario propagation are also performed to understand the changing dynamics. We finally discuss limitations, recommendations and directions for future research.