Siemens Hicom 300 Operator's Manual page 9

Option 1 - Hold for extension
What you have to do
Depress
If extension has not taken call in ±25
seconds it will recall to Console.
Option 2 - Try another extension
Depress
Procedure now as for normal extending
to free or busy extension.
Option 3 - Caller will call again later
Take message if required - then
Depress
What happens
Display shows
IDLE CONDITION
Caller is now camped-on to busy
extension.
Display shows
IDLE CONDITION
9