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What is the Fixed Dial Number (FDN) feature on my mobile device?
Fixed Dialing Number (FDN) mode, if supported by your SIM card, restricts your outgoing calls to a limited set of phone numbers. When this feature is enabled, you can make calls only to phone numbers stored in the FDN list on the SIM card.
FDN Mode must be set to On in the Menu > Settings > Phone > Security > Set FDN Mode option before you can add, change, or delete contacts on the FDN List.