Question: In a Voice Group Call Service (VGCS) scenario, what triggers the modification of VLR (Visitor Location Register) entries related to group IDs and subscription data for a service subscriber?
Option 1: Change in corresponding HLR (Home Location Register) records
Option 2: Periodic synchronization with neighboring VLRs
Option 3: Receipt of a new group call setup request from the subscriber
Option 4: Update of the subscriber's handset software
Explanation: In VGCS, ensuring a subscriber's service entitlement is consistently reflected across the network is crucial. When changes are made to a subscriber's records in the HLR, these updates must be propagated to the VLR to maintain service integrity and accessibility. Thus, modifications to corresponding HLR records directly trigger updates to VLR entries to keep the subscriber's group ID and subscription data current and accurate.