Question: What modes are Voice Group Call Service (VGCS) and Voice Broadcast Service (VBS) applicable to?
Option 1: A/Gb mode only
Option 2: Iu mode only
Option 3: Both A/Gb and Iu modes
Option 4: Neither A/Gb nor Iu modes
Explanation: According to the specifications, Voice Group Call Service (VGCS) and Voice Broadcast Service (VBS) are specifically designed for use in A/Gb mode only. This restriction is crucial for ensuring proper functionality and compatibility of these services within mobile networks.