A mobile communications system incorporates a plurality of home location registers on which subscriber data is stored such that each subscriber is allocated to a selected one of the registers for voice and/or data calls. Request messages for subscriber data can be routed to any home location register which responds to that request when the data for the respective subscriber is stored on that home location register. If the data for the respective subscriber is not stored on that home location register, the message is provided with an indicator component and is rerouted to another home location register for a further processing attempt. The number of times a message is rerouted is limited to prevent perpetual circulation of messages relating to unknown subscribers.