Question: In a Universal Subscriber Identity Module (USIM) Application Toolkit (USAT), when a 'call connect message' is triggered, which specific message defined in Mobile radio interface Layer 3 specification is equivalent to this event?
Option 1: DISCONNECT message
Option 2: RELEASE COMPLETE message
Option 3: SETUP ACKNOWLEDGE message
Option 4: CONNECT message
Explanation: According to the equivalences defined for call events in the context of USIM Application Toolkit, the 'call connect message' is specifically equivalent to the CONNECT message. This equivalence highlights how specific signaling messages relate to higher-level event notifications within the USAT framework, ensuring synchronized handling of call states between the network and the subscriber's equipment.