AASTRA 600d for Aastra 800 and OpenCom 100 User Guide EN - Manual (Page 64)

Basic Functions
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2. Or a subscriber is busy and you want to be called back. When you hear the busy
signal, press the
softkey briefly and confirm Callback with Ok.
The state-dependent menus are individually described at the end of the following
chapters.
Tip
For fast and convenient access to the state-dependent menus you can programme
one of the programmable keys with the
System Menu function (please refer to
the chapter entitled Key Programming starting on page 137).