Question: What happens to dialled digit strings when the 'Call control by USIM' service is activated on a Universal Subscriber Identity Module (USIM)?
Option 1: They are directly sent to the network for call setup without USIM intervention.
Option 2: They are stored in the Mobile Equipment (ME) for later processing.
Option 3: They are first passed to a USIM application for potential allowance, barring, or modification before the ME sets up the call.
Option 4: They are automatically converted into USSD strings for further processing.
Explanation: When 'Call control by USIM' is activated, the USIM exercises control over various operations, including call setup. This involves scrutinizing dialled digit strings through a USIM application, which can then decide to allow, bar, or modify the call request based on predefined criteria before the Mobile Equipment (ME) proceeds with setting up the call.