ID for purchasing prepaid mobile in Japan.
 

I have to tell that the ID requirement for the purchase of prepeid mobile is more strict than before even in the case of Softbank.
I now checked the web pages of Softbank. Now they officially require ID with Japanese address (Driving permit issued in Japan, certificate of foreigner's registration, Student ID from Japanse universities etc.) as well as au.
When it was still Vodafone Japan, some shops accepted foreign passport as ID and it was enough to write the address of your hotel in Japan. But it does not seem to work.

Yazcedric mentions about "anonymously sold prepaid cellphone". I also know their existence. They are sometimes offered even on internet auction sites. But I do not recommend it either. It is completely illegal. Stay away from it.
But, if one of your Japanese friends buys a prepaid cellphone and let you use it, there is no problem. I have already called au and Softbank to get the answer "OK" because I sometimes have foreign researchers visiting me and let them to use one of my prepaid mobile.

Anyway Japanese market of mobile communications is very special. In Japan, almost all the people think that they buy mobile hendset from the mobile operators and they can not understand that the handset and subscription contract can be separate.

If you can manage to get onto a US military base in Japan you may find it easier to obtain a prepaid phone without the Japanese ID. They seem to operate under an exception to the rules not available to everyone else.

oooh ok thanks for that people i am still really miffed i cant get my grubby mitts on some fiiiinnnnee nipponese phone gadgety type gadets....damm them...damm them all!

Softbank Prepid Sim Card in German Cellphone....
 

I have a Cellphon that can use UMTS (Sony Ericsson K800i) so I thought I could just get a prepaid SIM Card, insert it and use my phone in Japan...
Well, I got the card and I can make and receive calls. What does not work is SMS and Mails. My phone tells me it requires setup to be able to send or receive Mails...
The Softbank guys have no idea how to handle this problem. (In Tokyo I was told it is company policy to give Softbank Sim Cards only to people who already have a Softbank phone... Well, in the countryside they were merely concerned, that the card might not fit.)
The Sony Ericsson Homepage is not really helpful eigher. There is one setup download available, that aledgedly does it all by itself... which of course doesn't work. So I have to enter the settings manually.
Does anyone know Softbanks Connection type (pOP3 or IMPA4?), incoming server and outgoing server?

you can use web browser with following GPRS settings.

APN: softbank
username: ai@softbank
password: softbank

Email Settings are depending on your email provider, so you can set whatever you use on your normal computer as well.

Chris