A mobile number of a mobile device can be employed as an authorization factor when the mobile device is connected to a WLAN. When a user attempts to interact with a restricted access server via the mobile device, verification functions loaded on the mobile device determine whether the mobile device is connected to a WLAN. If so, the verification functions cause the mobile device to open a port on the cellular network interface of the mobile device and transmit data packets to a mobile device identification server via a cellular network. The mobile device identification server can then determine the mobile number of the mobile device based on the cellular network IP address of the mobile device, and transmit the mobile number to the restricted access server as an authentication factor.