When I was reading the book Smart Card Applications by Wiley and I came across the "EFADN file".
The EFADN (abbreviated dialing number) file of a SIM can be used here as a typical example. This file can only be read using the READ RECORD command if PIN 1 has previously been correctly verified by the smart card.
What is purpose of this file?
Abbreviated Dialing Numbers refers to short numbers that can be used to reach certain services. The best example is numbers associated with emergency services, e.g. 911.
EF ADN is part of the GSM spec, see ETSI GSM doc GSM 11.11.
EF is smartcard/GSM shorthand for Elementary File, or a regular data file in the filesystem. DF is shorthand for Directory. EF ADN is a telcom specific file located at: MF/DF_TELCOM/EF_ADN