Fixed Dialing Number (FDN) is a service mode of a GSM mobile phone's SIM card.
[1] A notable exception is that emergency calls to 000, 112, 911, 999 and the like are exempt.
[2] Incoming calls are not blocked by FDN.
[1] One practical application of FDN is for parents to restrict the phone numbers their children can dial.
[2] The SIM card's PIN2 must be entered beforehand or when applying such settings.