Question: What is the primary purpose of a Correlation MSISDN (C-MSISDN) in the context of IMS and CS domains?
Option 1: To provide a unique identifier for each IMS user.
Option 2: To enable multinumbering options for subscribers.
Option 3: To correlate sessions at access transfer and route calls from the IM CN subsystem to the same user in the CS domain.
Option 4: To define the organization of subscriber data.
Explanation: A Correlation MSISDN (C-MSISDN) is used for correlation of sessions at access transfer and to route a call from the IM CN subsystem to the same user in the CS domain, as stated in the provided text. This highlights its role in ensuring seamless communication between different network domains.