Xiaomi
Set Up Fixed Dialing Numbers (FDN) auf Xiaomi
Fixed Dialing Numbers (FDN) is a SIM card feature, not a phone setting. When it is active, only the numbers stored on the FDN list can be called or texted from that SIM slot. Every other number gets rejected instantly, which looks like a network problem but actually comes from this restriction.
Because FDN lives on the SIM, enabling or editing it always asks for PIN 2. This is a separate code from your everyday SIM PIN, usually supplied by your carrier. Enter it wrong too many times and the SIM can lock, so keep the correct PIN 2 ready before you start.
To reach the setting: Tap on Phone ➔ Open the Menu ➔ Tap on Settings ➔ Tap on Calling accounts ➔ Tap on Advanced settings ➔ Tap on Fixed Dialing Numbers ➔ Choose a SIM card (Dual SIM) ➔ Turn On/Off Fixed Dialing Numbers and set the FDN list.
Use FDN when you need to limit a device to a fixed set of contacts, for example a child's phone or a company line. For everyday use without restrictions, leave it turned off.