So far I've found some for Mixi and Livedoor.

Here are a few social networking apps for Japanese iPhone:

Mixi (FREE)
http://itunes.apple.com/WebObjects/MZSto...51864&mt=8

Mixi Browser on ROM (230 Yen)
http://itunes.apple.com/WebObjects/MZSto...26074&mt=8

MixiDock Mini (FREE)
http://itunes.apple.com/WebObjects/MZSto...51686&mt=8

Livedoor Clip (FREE)
http://itunes.apple.com/WebObjects/MZSto...20986&mt=8

Does anyone know of any others? How about for the Blackberry or G1 Phone or any other mobile phone/device?

Thanks.

I'd love to know as well, heh.
Just got a Blackberry Tour. Now I'm scrambling to figure out what to do with it. :p