Fixed Dialling Number (FDN) is a feature of a phone's SIM card that can restrict outgoing calls only to a special list of numbers, or to numbers that match a certain template.
A business can set up and use FDN as a security measure to prevent employees from dialling numbers outside the company from their corporate-paid account.
Note: Incoming and emergency calls are not affected by this option, so 911 and 112 are always reachable
1. Go to the Phone app > Tap the Menu Icon in the top right corner > and select Settings > select Calling Accounts.
2. Tap the image of the SIM card you wish to configure
3. Select Fixed Dialling Numbers (FDN).
4. In this screen you can enable/Disable FDN, you will need to know the PIN2 code. You can also manage the list of FDN from this page.