To have a cell phone in Japan

When you want to use cell phone in Japan, you have to buy or rental.
You can not use GSM cell phone.

In Japan, "PDC" is generation 2 of cell phone.
Now cell phone company want to switch to 3G.

NTT docomo, AU by KDDI and Softbank(former Vodafone Japan) provide.
My recommend is AU by KDDI.
They have support staff who can speak english. (Docomo & Softbank don't employ a lot of english speaker.)

AU have english web, catalogue and support line.

And you can have one more choice, "PHS".
It is more cheap to have than cell phone in Japan.
If you want to use Japanese smart phone, it is this.

You have to choose according to usage.