Update November 2014: Softbank has changed their WEP keys. This will no longer work. Sorry folks.

I finally figured out how to get wifi access using a laptop on the Shinkansen (Nozomi N700 only I think) or any Softbank “mobilepoint” access point. iPhone and iPad users will already have free “Softbank Wifi” access – this is normally locked to only an iPhone or iPad. Softbank only check your user agent.

• Select the access point “mobilepoint”
• Enter the WEP key: 696177616b
• On Lion, a wifi access window will appear showing the mobilepoint login screen. Close this if it appears.
• Open Safari
• On the Develop menu (this might have to be turned on in Preferences) select the correct user agent:
  • For iPad Wifi (which gets you “2 years free wifi”) or iPad Wifi/3G users, select “Safari iOS 4.3.3 – iPad”
  • For iPhone users, select “Safari iOS 4.3.3 – iPhone”
• Try and access a page in Safari and it should redirect you to the mobilepoint login page.
• Enter your Softbank username and password. For iPhone or iPad 3G users, this is the “[email protected]” email address and password for the IMAP account you never use. For iPad Wifi users, use the “[email protected]” account with the password written on the letter you got bundled with your wifi-only iPad.
• Since their portal now thinks you are actually logging in on the correct device, you have access. You can now stop using Safari and use Chrome/Firefox/Mail.app/whatever.