DND ON nailed it. "Overflow" is misleading, because the call is still ringing in the original HG. Think of "Announcement" and "Overflow" as the two places to put in greetings or transfer options for callers. They still remain in the HG while greetings play until they select an option that transfers them out. If you put a HG in either of these, the caller is still ringing in the original HG. "Recall" destinations actually transfer the caller from the HG to a destination.