5.16.18.3.2. User Interface 
A second acknowledgment tone signalizes to the user that the function
for inserting a call into the ON-hook queue can be activated.
Activation:
- Opti-Point
By confirming the menu "call back", insertion into the ON-hook queue is activated.
- Anate
By confirming the "flash key" and suffix dialing of the digit analysis result ACBK, insertion into the ON-hook queue is activated.