The zte0nu tool by user stich86 on GitHub works on latest firmware as of writing (V9.0.10P18N2B) and provides telnet access to router which then can be unlocked fully by using the upgradetest sdefconf 198 command.
github.com
GitHub - stich86/zteOnu: Little program that opens telnet on ZTE ONU\CPE
Little program that opens telnet on ZTE ONU\CPE. Contribute to stich86/zteOnu development by creating an account on GitHub.