Pre-orders and previews begin April 10, launches April 24.
iOS 6.1.2 to Address Exchange and Passcode Bugs Reportedly Coming Early Next Week
Like iOS 6.1.1 released for the iPhone 4S earlier this week, iOS 6.1.2 will be a limited update addressing only these issues in order to allow Apple to quickly release it to the public. Apple last week seeded to developers an initial iOS 6.1.1 beta including broader changes such as improvements to Maps in Japan, but it now appears that this release will become iOS 6.1.3 as Apple addresses a few high-priority bug fixes on a separate basis.
iPhone-Ticker has previously offered accurate information on iOS update schedules, including word of the iOS 6.1.1 update [Google translation] a few hours before it was released to the public.