What I did when I was recently in Japan was pick up the lowest of low end J-Phones for about $30. The plan they had allows anyone with a passport and credit card to charge phone calls to the card. Worked out surprisingly well.

Also, it amused (and annoyed) me to no end that the Japanese phone I had picked up for next to nothing made my much more expensive Canadian Telus brick look like a joke in comparison.
AND Telus didn't have a happy duck family waving goodbye whenever I turned the phone off. For shame, Telus, for shame.