Question: In a USIM application, when a Mobile Equipment (ME) needs to update the status of a forwarded call, which Elementary File (EF) does it use for the updating procedure, given that Call Forwarding Indication Status is supported?
Option 1: EF Phonebook (EFPHB)
Option 2: EF Service Provider Display Information (EFSPDI)
Option 3: EF Mailbox Dialling Numbers (EFMDN)
Option 4: Elementary File Call Forwarding Indication Status (EFCFIS)
Explanation: The correct answer is EFCFIS because, according to the specifications for the USIM application, when the Call Forwarding Indication Status service is available, the ME uses EFCFIS for both reading and updating procedures related to call forwarding indication status, ensuring accurate reflection and modification of call forwarding settings.