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According to Engadget, it would appear that users affected by this bug haven't updated past iOS 4.2.1. The most recent version of the iOS is iOS 5.0.1, which comes with a load of new features Apple added in iOS 5, including a new notification system, iMessages, a Reminders app and more.
However, if you're rocking an iPhone 3G or second-generation iPod touch, iOS 4.2.1 is the end of the line for you -- updating to iOS 5 isn't possible with those devices. Original iPhone owners (if there are any of you left!) can rest assured that the bug doesn't affect iOS 3.1.3.