Samsung SGH-E317CSACIN - Manual (Page 117)

Network Services
117
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.