Question: In a 3GPP system, what is a requirement for routing a Short Message over IMS to an emergency response centre (e.g., PSAP) when using emergency numbers?
Option 1: The message must always be routed based on the subscriber's home network location.
Option 2: The presence of a SIM/USIM/ISIM is mandatory in the UE for routing purposes.
Option 3: The message shall be routed to the emergency response centre serving the location where the subscriber is currently located.
Option 4: The routing decision is solely based on the type of device (UE) used by the subscriber.
Explanation: This option aligns with the principle that emergency services, including Short Message Services over IMS, should be directed to response centers based on the subscriber's current location. This ensures timely and relevant assistance, as per local regulations and the specifications for handling emergencies in telecom networks. The correct routing based on the subscriber's location is crucial for effective emergency response.