Samsung SGH E310 User Manual page 151

Settings
Default group: you may set a default CUG with
your service provider. If you have done so, you can
enable the Default group option on your phone.
When making a call, you are given the option of
using your default CUG, instead of selecting one
from the list.
Deactivate: deactivates the CUG function. This
option appears only when the default group is
enabled or a CUG index is selected.
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