Question: How can an Application Server hosting a Public Service Identity (PSI) be invoked as an originating Application Server in an IP Multimedia Subsystem (IMS)?
Option 1: By dynamically updating the Destination URI in outgoing SIP requests at the P-CSCF.
Option 2: Through manual configuration of the User Equipment's (UE) IMS settings by the end-user.
Option 3: By modifying the filter information within the subscription information of the users intending to use the service identified by the PSI.
Option 4: Via an automatic discovery process at the S-CSCF upon user registration.
Explanation: Modifying the filter information within the user's subscription is a method to direct SIP requests according to predefined rules, allowing the Application Server hosting the PSI to be invoked as an originating server. This approach aligns with the IMS's service control and filtering capabilities at the S-CSCF, ensuring that specific services (identified by PSIs) are made available to targeted users based on their subscription profiles.