A method of facilitating a multi-line mobile service, the method comprising: storing, in a network database: information associating international mobile subscriber identities, IMSIs, with Mobile Station International Subscriber Directory Numbers, MSISDNs, and information indicating whether the MSISDNs are active and whether the MSISDNs are enabled, wherein an indication in the network database that a particular MSISDN is active indicates that the particular MSISDN is available to potentially be used for inbound and outbound calls at a device with an associated IMSI, and wherein an indication in the network database that the particular MSISDN is enabled indicates that the particular MSISDN is set as the MSISDN to use for inbound and outbound calls at the device with the associated IMSI; receiving, by a network proxy from a visiting location register of a mobile switching center, MSC/VLR,, a mobile application part location update, MAP LUP, message that includes an IMSI of a mobile device that is registered with the MSC/VLR; determining, by the network proxy, a plurality of MSISDNs associated with the mobile device by looking up the IMSI in the network database, wherein the plurality of MSISDNs includes at least a first MSISDN that is active and enabled, and a second MSISDN that is active but not enabled; transmitting, by the network proxy to a home location register, HLR, a set of MAP LUP messages for a set of all active MSISDNs associated with the mobile device; receiving, by the network proxy from the HLR, a set of subscriber data for the set of all active MSISDNs associated with the mobile device; and transmitting, by the network proxy to the MSC/VLR in response to the MAP LUP message, subscriber data associated with the first MSISDN, based on the first MSISDN being enabled and the second MSISDN not being enabled, wherein the network proxy emulates the HLR during communications with the MSC/VLR by receiving the MAP LUP message from the MSC/VLR and responding by transmitting the subscriber data to the MSC/VLR. storing, in a network database: information associating international mobile subscriber identities, IMSIs, with Mobile Station International Subscriber Directory Numbers, MSISDNs, and information indicating whether the MSISDNs are active and whether the MSISDNs are enabled, wherein an indication in the network database that a particular MSISDN is active indicates that the particular MSISDN is available to potentially be used for inbound and outbound calls at a device with an associated IMSI, and wherein an indication in the network database that the particular MSISDN is enabled indicates that the particular MSISDN is set as the MSISDN to use for inbound and outbound calls at the device with the associated IMSI; information associating international mobile subscriber identities, IMSIs, with Mobile Station International Subscriber Directory Numbers, MSISDNs, and information indicating whether the MSISDNs are active and whether the MSISDNs are enabled, wherein an indication in the network database that a particular MSISDN is active indicates that the particular MSISDN is available to potentially be used for inbound and outbound calls at a device with an associated IMSI, and wherein an indication in the network database that the particular MSISDN is enabled indicates that the particular MSISDN is set as the MSISDN to use for inbound and outbound calls at the device with the associated IMSI; receiving, by a network proxy from a visiting location register of a mobile switching center, MSC/VLR,, a mobile application part location update, MAP LUP, message that includes an IMSI of a mobile device that is registered with the MSC/VLR; determining, by the network proxy, a plurality of MSISDNs associated with the mobile device by looking up the IMSI in the network database, wherein the plurality of MSISDNs includes at least a first MSISDN that is active and enabled, and a second MSISDN that is active but not enabled; transmitting, by the network proxy to a home location register, HLR, a set of MAP LUP messages for a set of all active MSISDNs associated with the mobile device; receiving, by the network proxy from the HLR, a set of subscriber data for the set of all active MSISDNs associated with the mobile device; and transmitting, by the network proxy to the MSC/VLR in response to the MAP LUP message, subscriber data associated with the first MSISDN, based on the first MSISDN being enabled and the second MSISDN not being enabled, wherein the network proxy emulates the HLR during communications with the MSC/VLR by receiving the MAP LUP message from the MSC/VLR and responding by transmitting the subscriber data to the MSC/VLR.