Foreign visitors have two choices; either buy a pre-paid minutes cell phone or rent a cell phone at a Japanese airport. I decided to buy a pre-paid cell phone, because I visit there at least once a year. By doing this, I have saved some money over the years, and at least kept the same number every time I visited Japan.
You would think that even if the cell phone system is different, I could use a smart phone to browse the Internet, check emails, and talk by Skype if I could pick up a Wi-Fi signal. But free Wi-Fi is hard to come by in Japan. The only true free Wi-Fi I found in Japan was at the airport in 2012.
Starbucks in Japan claims "free Wi-Fi spot", but their Wi-Fi connections are only available for the customers of a particular cell phone company. Surprisingly, McDonald's, coffee shops, and other places don't offer free Wi-Fi at all. I saw the smart phone I brought from the United States was picking up numerous signals wherever I went, but found they were all password protected.
If you stay in a hotel, you are provided complementary Wi-Fi connection as long as you are within range, but are out of luck once you wonder further away. I was staying at an apartment where there is no Internet connection. In order to get connected to the Internet, I had to ask the next door neighbor for Wi-Fi access. Graciously, the neighbor gave me his password.
I've been dreaming of the day I could use my phone in Japan, and pick up free Wi-Fi signals, but it doesn't seem likely to happen anytime soon.