Emergency calls on a subscription may fail for various reasons. For example, the core network may reject the call. Failures causes, for example, IMSI UNKNOWN IN VLR/ILLEGAL ME can happen at the mobile switching center (MSC) while setting up the call. These failures may occur when the mobile communication device is initiating a call on the visiting public land mobile network (VPLMN).
In some countries, networks mandate that an international mobile subscriber identity (IMSI) be used for the emergency call. Further, a network may reject the emergency call if the IMSI does not belong to the network home location register (HLR) database.
In case of failure, the mobile communication device will retry the emergency call on the same subscription multiple times, either immediately or after certain time with no guarantee of success.