A 5th-Generation (5G) cellular communication device may at times be used with a legacy subscriber identifier module (SIM) that does not support 5G subscriber identity privacy features. To obtain a subscriber identifier for authentication, the device attempts to obtain or generate a concealed subscriber identifier with the support of the current SIM. If this is not possible, as may be the case with legacy, non-5G SIMs, the device determines whether the home network specified by the SIM is the network of the provisioning operator. If so, the device obtains an unconcealed subscriber identifier from the SIM, encrypts it with the provisioned home network key, and uses the resulting concealed subscriber identifier for authentication. If the home network specified by the SIM is a network other than that of the provisioning network operator, the device obtains the unconcealed subscriber identifier from the SIM and uses it for authentication.