The update is available for the iPhone 3GS, iPhone 4, iPad, iPad 2, and both the third and fourth-generations of iPod touch. The update is not available for the Verizon/CDMA version of iPhone 4.
iOS 4.3.1 update fixes the following issues:
– Fixes an occasional graphics glitch on iPod touch (4th generation)
– Resolves bugs related to activating and connecting to some cellular networks
– Fixes image flicker when using Apple Digital AV Adapter with some TVs
– Resolves an issue authenticating with some enterprise web services
To update your iOS device, connect it to a computer with the latest version of iTunes. Then, open iTunes, and click through to the iOS device’s page inside iTunes. Finally, click Check for Updates on the right-hand side of the screen. Follow the instructions to walk through downloading and installing the software update. Apple encourages all users to update as soon as possible.