is there anyone who has jailbroken iPhone 3g Provided by Softbank in Japan?
Any success in this regard??
I am a guy who jailbroke my Softbank's iPhone, as tony-in-japan said previously. Did it because I needed some stuff which was not available on iPhone at that time (SSH access application was a must).
I jailbroke version 2.0 of iPhone, but bricked the device when trying to update it to 2.0.1 directly in iTunes. Got my iPhone replaced though (I never told Apple that problems were related to jailbraking of course).
If you really want to jailbrake, be ready to end up with bricked iPhone if you're not careful enough. Search for Pwnage tool on Google for more details on jailbraking.
One thing to be very careful about - once jailbroken, NEVER EVER update your iPhone's software directly in iTunes. First, wait for the updated version of Pwnage tool, then download software update WITHOUT installing it, apply the Pwnage tool patch, and restore the modified disk image onto iPhone.
Myself, I recently unjailbroke my iPhone, as the most critical application for me came out for iPhone and available in Japanese AppStore (TouchTerm). I still miss better notifications, but I am really tired of restoring iPhone from the scratch without ability to transfer applications' saved data every time a new firmware update comes out or something goes wrong (somehow backups from restore didn't work once for me on jailbroken iPhones) - so I just set ringer volume to max when I go to bed, so I won't miss important mid-night emais

. Having cracked games running on my iPhone was nice, but I never really used them. The few once I like, I just bought. So well, at current stage, jailbraking is not essential for me anymore...