In December, 2011 iOS 5.1 beta 2 was released to developers and now Apple pushed iOS 5.1 beta 3 build 9B5127a which is available as an Over-The-Air (OTA) for iOS 5.1 beta users or could be grabbed directly from iOS Dev Center.
The iOS 5.1 beta 3 is compatible for iPhone 4S, iPhone 4, iPhone 3GS, iPod Touch 4G, iPod Touch 3G, iPad 2, and original iPad.
Download iOS 5.1 beta 3