The iphone is cool, good interface, but it just isn't for me.
But no, I wouldn't want to switch from AU to Softbank. Although I'm not much of an AU fan these days either. I thought hard about switching to Docomo, especially since they had a phone that's only about 1/2 the thickness of mine. But the wife is on AU, and we get free calls between us if we are on the same company, so I stuck with AU.
I like my new phone though, it's nice, thin, and easy to use.