Mobile data services for Japan visitors
Google Maps seems to be properly in synch with local companies schedules and provided accurate results on how to go from point A to point B within the city. But to be able to use it you need Internet mobile access. And this is where Japan seems a bit odd for the visitor: It seems you cannot buy a prepaid voice or data SIM card unless you are Japanese. Maybe I am missing something here but that was what I learned from my online search.
One notable exception seems to be B-mobile VISITOR SIM, which offered pre-paid data service SIM card.
Fortunately, what you cannot buy, you can rent. So there are a handful of companies that can rent you a SIM card provided you are carrying an unlocked phone. Or else you can rent a phone too, this way you are certain the phone is going to play nice with the SIM card. But what surprised me the most was the availability of mobile wifi hot-stops, that will get their Internet from 4G or WiMAX networks and will offer wifi connectivity to all the devices within a few meters of the unit. This mobile hotspot is similar size of a cellphone and with a battery that will last for a few hours of operation.
In the end, we were lucky because the Japanese hospitality of our friends provided us both, a voice SIM card and a mobile wifi/WiMAX device for free. That meant the whole family was able to be online all the time using the wifi hotspot. I totally can recommend this type of service even if you have to pay for it as it worked nicely not only in the cities but also in our Shinkansen rides.
Finally, another service worth mentioning are public wifi networks. The one I used was Wi2, that offered one day of free wifi for VISA card holders. I used the free service to log on the Internet on arrival during our ride on the Narita Express train that connects the airport with the city. It may not work everywhere but it worked for us and it did not cost us a dime.