Question: In a Mobile Station (MS) or User Equipment (UE), what is the primary implication for the device's operational state when it enters "Emergency Calls Only Mode" due to a failed personalisation check?
Option 1: The MS/UE can only access data services but not voice call services.
Option 2: The device reverts to an earlier firmware version to maintain basic functionality.
Option 3: All services are completely disabled except for receiving SMS from the network.
Option 4: The MS/UE enters a "Limited Service State", allowing emergency calls using TMSI and IMSI from the SIM/USIM.
Explanation: When a personalisation check fails, the Mobile Station (MS) or User Equipment (UE) enters "Emergency Calls Only Mode". This mode is equivalent to the "Limited Service State", as defined in NAS functions related to Mobile Station (MS) in idle mode. In this state, despite the failed personalisation, the device can still access and utilize the Temporary Mobile Subscriber Identity (TMSI) and International Mobile Subscriber Identity (IMSI) from the Subscriber Identity Module (SIM)/Universal Subscriber Identity Module (USIM) for emergency call purposes. This highlights the balance between security (through personalisation checks) and accessibility for critical services like emergency calls.