I have been forwarded a program h235tounlock.c to unlock the Inventel Livebox and allow it to be used with any ISP. I have made a binary for x86 Linux h235tounlock and an executable for DOS h235tounlock.exe. Instructions for use are contained within the h235tounlock.c program and are repeated below. Thanks to pcmaster, here is now an html program that will generate the unlock code.
To use this program you need to get the H235 key that is stored in the flash of the Livebox. The only way that I know to do this is to get to a console on the Livebox. I have managed to get a console on my Livebox without using the Serial Port by automatically downloading a Telnet server to the Livebox. See Telnet Access for more details.
Once you have managed to get to a command prompt you need to do the following,