I now see what the problem is. There is a configuration option to disallow config updates through the phone keypad. If you enable this, the phone won\'t allow you to hard reset it either.
So if you enable this option and you forget your password, your phone is stuck and you can\'t change the configuration anymore. Basically you bricked it. I managed to recover my password so I was lucky.
This is a really bad design choice by GS. In every apparatus there should be an option to hard reset it at all times.