Samsung SGH-x427 User Manual page 130

Network Services
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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