How do I unlock 3G Docomo Japan Vita

I have a Japanese PCH-1100 Docomo vita, is there a way to use my iphone 5's SIM card with something like I smart sim? I live in the U.S. And I already tried my AT&T SIM card with an adapter so that it will fit the sim tray of my American PCH-1100 vita as the iPhone 5 uses a smaller sim.I plan on buying white red and blue pch-1100 3G vitas but they are Japanese only. I do not want to spend time finding good motherboards for them.