Bringing a bad ESN phone to Japan?

Will it work? I know it'll work for sure if it's unlocked (as i've researched on the internet) but I'm wondering if it'll work if I bought it in the US with a bad ESN. Will Japanese carriers mind? will a prepaid sim-card work?

Thanks!

First off it will need to be 3G W-CDMA to even work in Japan.

Other than that, the carriers seem to relatively strict concerning activating Japanese phones with bad ESNs. I can't imagine they are any more forgiving with foreign phones.

If you are looking to purchase a phone with a bad ESN due to the cost savings then I'd save yourself the trouble and get something that you would have better confidence in working. Otherwise if you already have your phone, then it wouldn't hurt to bring it and see if it'll work before looking into other routes.