Question: What files are mandatory on a USIM to support phone book synchronization with other devices, assuming synchronization is enabled for the phonebook?
Option 1: Only Phone Book Synchronisation Counter (PSC) and Unique Identifier (UID)
Option 2: EFPSC, EFUID, and EFCC (but not EFPUID)
Option 3: EFPSC, EFUID, EFPUID, and EFCC
Option 4: Phone Book Synchronisation Counter (PSC), Unique Identifier (UID), and Change Counter (CC) without EF prefixes
Explanation: To ensure seamless synchronization of phone book data between devices, the USIM must provide specific files. According to telecom standards for USIM applications, if phonebook synchronization is supported, all four files - EFPSC (Phone Book Synchronisation Counter), EFUID (Unique Identifier), EFPUID (another form of Unique Identifier often related to the user or device), and EFCC (Change Counter) - are mandatory. This comprehensive set ensures that changes can be accurately tracked and synchronized across devices.