As a public service announcement for those toting Apple mobile devices with a few more scratches than the average iPhone 4S: iOS 5 is compatible (and that includes iMessage functionality) with the following devices:
- iPhone 3GS
- iPhone 4
- iPad 1
- iPad 2
- iPod Touch 3rd Generation
- iPod Touch 4th Generation
The bottom of the iOS features page has more information from Apple.
And, of course, connect your device to iTunes and update.
And, of course, connect your device to iTunes and update.