Gigaset HiPath 3000 V3.0 or later M1 Professional Operating Instructions Manual page 71

Group functions
Step-by-Step
> <
Service?
> <
More features:
> <
#501=Forward Line:
Off?
64
Forwarding off
c
Press the Talk key.
Call the system menu.
Menu
[
Select and confirm the menu item.
[
Select and confirm the menu item.
[
Select and confirm the menu item.
o
Enter a line number.
a
Press the On-hook key to end the process.