Question: What is the location update status when a mobile station's last location updating attempt was successful, and it contains a valid LAI of the location area where the subscriber is registered?
Option 1: U2 NOT UPDATED
Option 2: U3 ROAMING NOT ALLOWED
Option 3: U4 UPDATING DISABLED
Option 4: U1 UPDATED
Explanation: According to the text, when a mobile station's last location updating attempt was successful, and it contains a valid LAI of the location area where the subscriber is registered, the location update status stored on the SIM/USIM shall be "updated", which corresponds to U1 UPDATED.