Pre-orders and previews begin April 10, launches April 24.
Apple Seeds iOS 6.1.3 Beta 2 to Developers with Fix for Passcode Lock Bug
Release notes for the original beta version had indicated that it focused on Maps improvements for Japan, and Apple indicates that the beta now addresses the passcode lock bug publicized last week.
The release of the new beta comes just over two weeks after the release of the first beta version, although at least part of Apple's team has undoubtedly been sidetracked by rushing the emergency Wi-Fi and Exchange bug fixes through development. A target date for a public release of iOS 6.1.3 is unknown.