US Firmware on Jap PSP?

i plan on getting a White PSP of Lik-Sang pretty soon and i'm assuming it will have 2.0+ firmware and to my knowldge there are only Jap PSPs out right now. yes i know there are no current ways of downgrading from 2.0+ but i am sure there will be sometime.

My question is, will US firmware (1.0 or 1.5) work on a Jap PSP?

I have a Multi-Regional Cermaic PSP :) Im sure ALL white PSP's released in Japan are the same :)