A method and system for selectively providing cellular offload services to mobile user data devices via vehicle-based access points. Subscribers and affiliates of vehicle-related online services register their user data devices for authorized connections. Vehicle metrics are used to determine the state of a vehicle (being driven or parked), and the metrics of the user device can be compared with the vehicle metrics to determine if the user device is inside the vehicle. Limiting access to authorized user devices reduces load on the vehicular access points and allows preventing the vehicular access points from being erroneously included on access point maps and thereby infecting the maps.