Question: What type of information element may be sent by the network to the calling mobile station during call establishment when interworking with another network or non-PLMN/ISDN equipment is detected?
Option 1: A progress indicator information element containing a progress description value indicating that the call has been successfully established.
Option 2: A call control message with a state change request, but without any additional information about the interworking situation.
Option 3: A progress indicator information element containing one of the specific progress description values (#1, #2, or #4) to inform the mobile station about the interworking situation.
Option 4: An error message indicating that the call cannot be established due to interworking issues.
Explanation: The correct answer is Option 3 because when interworking with another network or non-PLMN/ISDN equipment is detected during call establishment, the network may send a progress indicator information element to the calling mobile station. This information element contains one of the specific progress description values (#1, #2, or #4) to inform the mobile station about the interworking situation, as specified in the 3GPP TS 24.008 standard.