I'm new to this stuff so excuse me if this already covered somewhere - but I don't care about being able to call or text in Japan (Tokyo, Kyoto), am just wondering if I can use any of my apps - a translator app, walking maps that use GPS, currency converter, etc. I guess maybe over Wifi if I can find it? But will I get charged at all? And what do I have to do to only use Wifi and not get charged roaming? Thanks!!