KONAKA-RESIDENCE IS WIFI FREE RESIDENCE
As my experiences, (japan-France commute since 20 years), there is no prepaid-portable telephone in japan on 2012. Before you could buy your prepaid telephone card, but it is finished because of crime uses.
Why? Because in Japan, it is impossible to find SIM FREE PHONE or SMART PHONE in the store, maybe you will find at small street on Akihabara or Nihonbashi but Normal store in the city or internet. but officially it is not allowed SIM FREE PORTABLE PHONE in Japan.
So what should You do?
I strongly recommend you to bring to Japan, your own SIM FREE SMART PHONE or iPhone then you will buy the prepaid sim card as I show you blow.
It is little bit complicated. Because it is needed your address in japan. Those who stay in my place for 2 month, it is very useful, but traveler like you, stay only tree days or one week, it is kind of complicated. Otherwise you will rented your portable phone at airport Kansai, when you enter Japan.
Even the Starbucks or Mac Donalds in japan there is no free wifi systems. so Please find your wifi free cafe or Hotel at the first when you arrive in Japan!