Cheapest would be Yahoo BB. It is somewhere around 7 yen for 3 min. I had a Pre-Kei(prepaid cell) from a company called Tuka. The cards were 1000, 3000, and 6000 yen for an alloted amount of minutes. I never made any calls, I used the cards up for text messages. It is free to recieve calls on these, so my folks would call me. If I wanted to call out I would buy a Brastel phone card and use a pay phone at a local convenience store.