Provided is a vehicle communication system and a mobile device that make it possible to automatically open a vehicle door without impairing security or convenience. A vehicle communication system includes: an on-board device (1) that outputs a control signal for opening a vehicle door (D); and a mobile device (2) that transmits a reservation signal pertaining to a reservation for opening the vehicle door (D), to the on-board device (1), the on-board device (1) outputting the control signal by performing predetermined communication with the mobile device (2) upon receiving the reservation signal. The mobile device (2) includes: a mobile transmission unit that transmits the reservation signal; an acceptance unit that accepts an operation pertaining to transmission of the reservation signal; and a transmission control unit that causes the mobile transmission unit to repeatedly transmit the reservation signal upon the acceptance unit accepting the operation.