thanks for the replies. Seems like I didn't managed to install the USB Network successfully.
What I'm doing:
I'm mounting the Kindle as Storage device. I create file ENABLE_DIAGS in the root of it. Then I go to Settings -> reboot. After that the kindle start in USB network mode, but seems its not from the USBNetwork package, because I can't log with no password, not even with mario, or with fiona***. When I nmap the device.. there is no 20 (telnet) port opened.
Not sure what I've done wrong. How can I check if USBnetwork package is installed OK? And how can I assure my Kindle is jailbroken?
Maybe the biggest mistake was to update to the latest firmware version from amazon :/
Thanks in advance for the answers.