I just found out while reading casually, that the paperwhite 3G, for the version bought in Japan, has free 3G only in Japan!
There is no worldwide 3G coverage for the japanese PW 3G.
This is unlike the US version that has global 3G coverage.
This means that it is no use to take the PW 3G out of Japan, if we buy the japan version.
Japanese version: http://www.amazon.co.jp/gp/product/B...f=famstripe_ks
Looks like I will be getting the wifi version after all...