A method for establishing secure wireless communications between a mobile device and a vehicle, where a user is not required to enter a password, but instead the telematics system is used to bootstrap the trust between the mobile device and the vehicle. The user initiates the process by pressing a button on the mobile device to request pairing. The vehicle uses its secure OnStar cellular communication link to verify the mobile device with the OnStar server, which generates and sends a session key to the vehicle via the vehicle-OnStar cellular connection, and also sends the session key to the mobile device via the device's own cellular connection. The session key serves as a shared secret, such that the vehicle can issue a secrecy challenge to the mobile device. When the mobile device responds appropriately, a trusted wireless communications link can be established between the mobile device and the vehicle.