After hot dicussion in the past days on mobileread forum,the hacking of Kindle International becomes possible, at last. :)

Firstly, it was done by jyavenard, who introduced a reallyreally smart solution without hardware modifications. 
Blogkindle's description of this method is:" Unfortunately Amazon did use the asymmetric encryption to sign the packages. …… Kindle doesn’t use just one key to verify the signature – it enumerates all key files in /etc/uks directory and if any of the keys yields a positive signature validation – the file passes the test. So Jean-Yves Avenard created a tarbomb that would add extra public key to that directory."

Also, he has updated the script for hacks generation, along with his private/public key pair. So it's suggested to use ONLY this key pair to make other hacks, avoiding users from Jaibreaking their kindle again and again....

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Step.1 Jaibreak the Kindle international, download update_freekindle-k2i.bin (or from my site's update_freekindle-k2i).
    Copy the file update_freekindle.bin on the Kindle USB disk ; then:
    go to HOME
    MENU -> Settings
    MENU -> Update Your Kindle
    DO NOT SELECT RESTART, or you will brick your Kindle 
    (though there's a way to get out of that infinite reboot)
    That update will fail ! (Error 004). This is normal. Then, it's done.
Step.2 Now we can install hacks just as before. Jean-Yves Avenard also made new version of ScreenSaver Hack & Savory Hack. (My mirror)
Step.3 Check the Unicode Hack from blogkindle, he also made a anti-brick hack, take a look :)