A device for operating in a communication system that comprises a plurality of individual networks and each network in the plurality of individual networks being a mobile network, wherein: the device comprises at least two subscriber modules for assisting the device to attach to at least three networks of the plurality of individual networks , the number of those at least two subscriber modules being fewer than the number of the at least three networks ; and the device is configured to: before establishing a connection with one of the at least three networks , initiate a pre-attach procedure by transmitting a multi-attach request to a subscriber server to attach the device to all of the at least three networks , wherein the multi-attach request comprises an indication that it is a multi-PLMN attach message; wherein the device is configured to initiate the pre-attach procedure in dependence on triggering events including one or more of: switch-on of the device ; a determination that the device is approaching a border of a zone that is assigned to a network of the plurality of individual networks different from a network that the device is currently attached to; and receipt of information from a network relating to network loading and/or a type of service that can be accessed through one or more networks of the plurality of individual networks ; and connect to one of the at least three networks for communicating data with that network while remaining attached to the others of the at least three networks . the device comprises at least two subscriber modules for assisting the device to attach to at least three networks of the plurality of individual networks , the number of those at least two subscriber modules being fewer than the number of the at least three networks ; and the device is configured to: before establishing a connection with one of the at least three networks , initiate a pre-attach procedure by transmitting a multi-attach request to a subscriber server to attach the device to all of the at least three networks , wherein the multi-attach request comprises an indication that it is a multi-PLMN attach message; wherein the device is configured to initiate the pre-attach procedure in dependence on triggering events including one or more of: switch-on of the device ; a determination that the device is approaching a border of a zone that is assigned to a network of the plurality of individual networks different from a network that the device is currently attached to; and receipt of information from a network relating to network loading and/or a type of service that can be accessed through one or more networks of the plurality of individual networks ; and connect to one of the at least three networks for communicating data with that network while remaining attached to the others of the at least three networks . before establishing a connection with one of the at least three networks , initiate a pre-attach procedure by transmitting a multi-attach request to a subscriber server to attach the device to all of the at least three networks , wherein the multi-attach request comprises an indication that it is a multi-PLMN attach message; wherein the device is configured to initiate the pre-attach procedure in dependence on triggering events including one or more of: switch-on of the device ; a determination that the device is approaching a border of a zone that is assigned to a network of the plurality of individual networks different from a network that the device is currently attached to; and receipt of information from a network relating to network loading and/or a type of service that can be accessed through one or more networks of the plurality of individual networks ; and connect to one of the at least three networks for communicating data with that network while remaining attached to the others of the at least three networks . <EOS>