Japanese customers can use an unlocked iPhone for 6260 yen per month unlimited data packet use includes some voice calls

"The 6,260-yen fee (about $73.30) includes unlimited data packet communications and a 1,050-yen voice plan. Phone calls outside the voice plan will be billed at 21 yen per 30 seconds."

Japan Communications Inc will provide package for unlocked iPhones in Japan using NTT's network

Source:Unlocked iPhone 4s to use NTT cellular net
BY SHINYA WAKE
THE ASAHI SHIMBUN
2010/08/25
http://www.asahi.com/english/TKY201008240351.html