Abstract: A cellular radio communications system comprises: at least one base station for broadcasting radio signals to mobile stations within a cell; a mobile station addressable using IP addresses; and a first controller in the cell of the cellular radio communications system, the first controller being adapted: (i) to receive a request from the mobile station that the cellular radio communication system assign to the mobile station the static IP address previously assigned to the mobile station outside of the cell; (ii) in response to the request from the mobile station, to check with a second controller associated with the location where the mobile station was previously registered that the static IP address has not been assigned to another mobile station; and (iii) to assign the static IP address previously assigned to the mobile station, outside of the cell, to the mobile station for use in the cell, if the static IP address has not been assigned to another mobile station.