Controlling mobile-device roaming

Media and systems for controlling roaming of a mobile device on a wireless-communications network are described. Wireless-communications systems along a coverage area border are designated as roaming border systems. A parameter value is communicated from wireless-communications systems of a home network to a mobile device. The parameter takes on a value indicating whether a mobile device is permitted to initiate a connection to a roaming network. A mobile device is restricted to use of home-network systems when a first parameter value is received. The mobile device is permitted to use home-network and roaming-network systems when a second parameter value is received. Thus, the mobile device can only roam when the second parameter value has been communicated thereto.