The invention provides a method and system for locally tracking network usage and enforcing usage plans at a client device. In an embodiment of the invention, a unique physical key, or token, is installed at a client device of one or more networks. The key comprises a usage application and one or more access parameters designated the conditions and/or limits of a particular network usage plan. Upon initial connection to the network, the usage application grants or denies access to the network based on an analysis of the current values of the access parameters. Therefore, network usage tracking and enforcement is made simple and automatic without requiring any back-end servers on the network while still providing ultimate flexibility in changing billing plans for any number of users at any time.