AASTRA DT4x2 for MX-ONE User Guide EN - Manual (Page 42)

Outgoing Calls
DT412/DT422/DT432 42
When you receive a busy tone
If you call an extension and receive a busy tone, or get no answer,
or all external lines are busy, you can use any of the following
methods:
Callback
If a called extension is busy or there is no answer: 6
Press.
Note: France, Finland and Sweden, press
5
æ
Press to finish the procedure.
You are called back (recall ring signal) when the ongoing call is
finished or the next time a new call is finished. You have to answer
within eight seconds, otherwise the Callback service is cancelled.
While waiting for the Callback, you can make and receive calls as
usual. æ
Press when you are called back.
The system calls the extension.
Note: Callbacks can be activated on several extensions at
the same time.