Use APKPure App
Get GSM Secret Code Library old version APK for Android
Help every mobile phone user.
The GSM standard allows most of the functions to be controlled by entering codes into the keypad of a mobile phone: you can set diverts and the like, accept or reject calls, or even change your PIN code by typing at the keypad.
Unfortunately, not all the codes listed here are enabled by every network. If a code isn't supported, it simply won't work