When placing a caller on hold/parking a call, the caller will hearing the 'Background Announcement' greeting while they are waiting.
If you have set up department voice mail and all users/employees are busy, the caller will hear the 'Everyone Busy' greeting , before hearing a beep to record a message. Your greeting should inform the caller to start recording after the beep.
If you have not set up voicemail, and all users/employees are busy, then your call will hear the 'Hold message' greeting.
Extension Transfer Initiated
When you dial the extension of the user/employee you are trying to reach, you will hear this message. The default for this message is 'Please hold. You are being transferred.'