Question: What is the primary purpose of the EFACM (Accumulated Call Meter) file in a Universal Subscriber Identity Module (USIM) application?
Option 1: To store the International Mobile Subscriber Identity (IMSI) for authentication purposes.
Option 2: To provide an indication to the user for advice or calculate the monetary cost of calls by accumulating call units.
Option 3: To manage the storage capacity of the UICC for different applications.
Option 4: To secure the GSM and USIM application interfaces from unauthorized access.
Explanation: The EFACM file accumulates total call units for current and preceding calls, used to advise the user or calculate call costs, aligning with Advice of Charge (AoC) supplementary services.