Question: In IMS (IP Multimedia Subsystem) according to 3GPP Rel-5 specifications, what is the status of standardization for transporting specific information between the MRFC (Media Resource Function Controller) and the Application Server (e.g., IM-SSF)?
Option 1: Fully standardized, including all SIP methods for interactive voice services.
Option 2: Not standardized for certain procedures (e.g., returning Prompt_and_Collect results, play announcement completion notifications).
Option 3: Partially standardized, with only the MRFC to IM-SSF request protocols defined.
Option 4: Standardized exclusively through proprietary extensions.
Explanation: According to the provided context, specific SIP methods for interactions between the MRFC and the Application Server (like IM-SSF) in IMS have not been standardized. This includes methods for returning Prompt_and_Collect results, sending notifications of play announcement completion, and requesting the MRFC to play announcements or prompt and collect user information.