Here is why I think Google’s Strategy In Japan: Avoid Yahoo And Take Over The Mobile Web First will fail.
You can see from the Engadget pages about Softbank pages where they show a close up from the mobile phones where the key is located. Softbank being an investor in Yahoo! Japan has a huge leverage and I don’t think that being inside the operator/carrier menu will bring market share to Google.
Being a physical key in your phone is an advantage that can’t be dismissed because not everyone knows how to access every function of their mobile phone.