If You Cannot Reach a Destination ...

If a user is busy or is not answering, you can store an automatic callback. This feature saves you from having to make repeated attempts to reach the user.
You receive a callback, 

When the other party is no longer busy

When the user who did not answer has conducted another call.

Storing a Callback

Precondition: You have reached a busy line or no one answers. 

Confirm. 

Enter the code. 

Answering a Callback

Precondition: A callback was saved. Your telephone rings. "Callback: ..." appears on the display. 

Lift the handset. 

Press the key. The LED lights up. 

You hear a ring tone. 

Checking and Canceling a Saved Callback

Select and confirm. 

Enter the code. 

Select the displayed function and press the "OK" dialog key to display additional entries. 

Deleting a displayed entry:

Press the "OK" dialog key to confirm your selection 

Ending callback display:

Select and confirm. 

Press the key. The LED goes out. 

Press the key. The LED goes out.