I would like to give you a few hints about mobiles in Japan.
For those who visit Japan just for a couple of weeks,
it’s a bit cumbersome to stay connected.
This means you use your phone with your SIM as you would do inside your home country.
Unless your phone is a 3G Phone with the capability to send at the 2.1GhZ Band, your phone might not work inside Japan. On the other hand usually the home-providers let you pay a fortune for this easement.
This might be the cheapest way to get hold on a Japanese mobile but …
Due to national regulations it’s prohibited for mobile-carriers to sell phones to “unregistered aliens”, you need to register yourself. This could take a while for you to get through all all the Japanese red-tape. So it might be only a option for long term visitors.
They all have there benefits and disadvantages.
Softbank for instance is nearly omnipresent at all airports (including Fukuoka) and rather cheap (if ordered in advance via internet). But Softbank doesn’t allow any type of smart-phones.
This is a advantage of PuPuRu who offers an all around carefree package (including free domestic calls, free mobile internet, free mobile mail, voice box, etc.) for ~16’000Yen (~180USD or ~145EUR) for a 30day plan.
So please inform yourself carefully and choose wisely.
Have Fun in Japan