Question: For an IP Multimedia Subsystem (IMS) Centralized Services (ICS) subscriber, where should on-line charging be performed when utilizing both IMS and CS (Circuit Switched) networks?
Option 1: Concurrently in both IMS and CS networks to ensure comprehensive coverage.
Option 2: Exclusively in the CS network for streamlined billing processes.
Option 3: Strictly within the IMS, with CS network-based on-line charging services (e.g., CAMEL prepaid) not invoked.
Option 4: Dynamically chosen between IMS or CS based on the type of call (voice/data) initiated.
Explanation: This is correct because, according to specified guidelines for ICS subscribers, on-line charging must be performed strictly within the IMS framework, ensuring unified and standardized billing practices for services utilized through the IMS.