Yes. Softbank have updated to iphone 3.0 and yes jailbreaking is possible with redsn0w. Tethering isn't a on the menu or settings- atleast I haven't found it yet but if you Iphone is jailbroken then you can down load PDAnet on cydia and use that for tethering. I'm not sure if or how you would be charged for doing it but you would be breaking your terms and conditions with Softbank though.