Question: In a GPRS network (A/Gb mode), when a Mobile Station (MS) enters a new Public Land Mobile Network (PLMN), what action must the MS take, unless specified exceptions apply?
Option 1: Perform a Location Area Update immediately
Option 2: Perform a Routeing Area Update
Option 3: Initiate a Combined Location and Routeing Area Update
Option 4: No update is required for PLMN change
Explanation: When an MS enters a new PLMN, it must perform a Routeing Area Update, unless exceptions apply. This ensures the network is aware of the MS's new location for packet-switched services.