An apparatus configured to operate as a communication device that is part of a group comprising two or more communication devices that share a subscription to a communication network, the apparatus comprising: an identity module receiver for receiving an identity module, the identity module storing at least one of a static Group ID and an alias for the static Group ID, wherein the static Group ID is associated with the shared subscription that is stored prior to an initial authentication of the communication device and the alias for the static Group ID is stored after the initial authentication of the communication device, wherein the alias is utilized instead of the static Group ID of the group during subsequent communications after the initial authentication of the communication device, and wherein at least one of the static Group ID and the alias is used to obtain, group authentication information that is associated with the shared subscription, from the communication network; a transmitter for sending a service request to an authentication server within the communication network, wherein the service request includes at least one of the static Group ID and the alias, as an identifier for the group; a receiver for receiving a group authentication challenge from the authentication server, at least a part of the group authentication challenge having been generated using the group authentication information that is associated with the shared subscription; a processor for generating a device specific authentication response (RES') to the group authentication challenge using the group authentication information, device specific authentication information, and information provided by the identity module, wherein to generate the device specific authentication response, the processor is operable to generate a group authentication response using at least a part of the received group authentication challenge, and wherein the processor is further operable to generate the device specific authentication response by applying a pseudo-random function to the group authentication response using the device specific authentication information; said device specific authentication information comprising a device private ID derived from a device public ID of the communication device and wherein the transmitter is further operable for sending the device specific authentication response to the authentication server in a message. an identity module receiver for receiving an identity module, the identity module storing at least one of a static Group ID and an alias for the static Group ID, wherein the static Group ID is associated with the shared subscription that is stored prior to an initial authentication of the communication device and the alias for the static Group ID is stored after the initial authentication of the communication device, wherein the alias is utilized instead of the static Group ID of the group during subsequent communications after the initial authentication of the communication device, and wherein at least one of the static Group ID and the alias is used to obtain, group authentication information that is associated with the shared subscription, from the communication network; a transmitter for sending a service request to an authentication server within the communication network, wherein the service request includes at least one of the static Group ID and the alias, as an identifier for the group; a receiver for receiving a group authentication challenge from the authentication server, at least a part of the group authentication challenge having been generated using the group authentication information that is associated with the shared subscription; a processor for generating a device specific authentication response (RES') to the group authentication challenge using the group authentication information, device specific authentication information, and information provided by the identity module, wherein to generate the device specific authentication response, the processor is operable to generate a group authentication response using at least a part of the received group authentication challenge, and wherein the processor is further operable to generate the device specific authentication response by applying a pseudo-random function to the group authentication response using the device specific authentication information; said device specific authentication information comprising a device private ID derived from a device public ID of the communication device and wherein the transmitter is further operable for sending the device specific authentication response to the authentication server in a message.