Traveling to Japan and need to be able to use iPhone with Soft bank?

Question:

Will soft bank unlock my phone or do i have to get att to do it?

Answer:

It's not a matter of unlocking.

The question is, will you be using AT&T's international roaming/data plans? If so it will be using softbank's network, but AT&T will be charging you ( ALOT).

My recommendation is, forget about it. Instead, either rent a Japanese iphone in Japan, or rent a mobile wifi device, so you can use your iphones wifi for data and just use skype for international calling.