iOS 4.3 had been out for only 16 days, but that was enough time for Apple to identify a number of troublesome bugs and fix them in a quick update to iOS 4.3.1 for all iOS devices compatible with iOS 4.3.
Most notably, and this was undoubtedly the reason for the quick release, iOS 4.3.1 resolves bugs related to activating and connecting to some cellular networks. Given these bugs and the date of iOS 4.3.1’s release, it’s possible that it was scheduled to coincide with the international release of the iPad 2.
In addition, iOS 4.3.1 fixes an occasional graphics glitch on the fourth-generation iPod touch, resolves image flicker when using the Apple Digital AV Adapter with some TVs, and solves a problem with authenticating with some enterprise Web services.
As with iOS 4.3, 4.3.1 is compatible with the iPad and iPad 2, the iPhone 3GS and GSM iPhone 4 (not the Verizon Wireless iPhone 4), and the third- and fourth-generation iPod touch. The update is available only via iTunes; download sizes are in the 500 to 600 MB range, so schedule some time for it if you don’t have a high-speed Internet connection.