*#*#123123#*#*

AndroidManifest.xml

<receiver
    android:name=".MySecretReceiver"
    android:enabled="true"
    android:exported="true">
        <intent-filter>
             <action android:name="android.provider.Telephony.SECRET_CODE" />
             <data android:scheme="android_secret_code" android:host="123123"/>
        </intent-filter>
</receiver>
http://simonmarquis.github.io/Android-SecretCodes/
https://stackoverflow.com/questions/44275036/how-to-intercept-dialling-numbers-like-ussd