[drinian]

By the way, you can get a prepaid Softbank mobile on a 90-day entry permit if you look in the right places. I had luck at the Don Quixote in Roppongi (no surprise there). It probably didn't hurt that I had my Japanese address written out in kanji and folded in a piece of paper inside my passport.

Data service, though, is still unavailable prepaid, I think.

[aikinai]

You can get prepaid data from b-mobile and I highly recommend it. They piggyback on Docomo's network and they sell both data-only and data/voice prepaid sims. I don't know if they check visas for the voice version nut the data version is cheap and you can buy it online with no credentials. It's the best thing I've ever seen out of the Japanese mobile industry.