A few months ago, we wrote RT::Extension::MobileUI to give RT a mobile interface. We liked it so much that we quickly integrated it into RT 4.0, fixing some bugs along the way.
If you’ve already installed the extension, you should disable and uninstall it before upgrading to RT 4.0. When you do upgrade to 4.0, it’ll already be there ready for you.
For more information, see our original blog post about the mobile UI.