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I have a boingo account which gets me WiFi access with all of the major WiFi service providers in Japan. We'll be in Tokyo, Osaka and Kyoto with side trips to country areas. Do I need a SIM as well? If so with an iPhone 5, what's the best data option that support VoIP or App like Viber?
If you're planning to use Boingo in Japan, go to the "settings" and then "help" in the Boingo app. There you will find a list of WPA2 keys to connect to the various wifi networks (NTT Docomo, Mobilepoint). All the McDonald's in Tokyo I have visited had Mobilepoint wifi. A lot of the coffee places and restaurants had them too. Boingo was successful in connecting about 50% of the time, even at NRT, on their own network!!
Starbucks has their own free network. Go
here to sign up before you start your trip.