It’s been a long time coming, as the last developers beta for iOS 5.1 was released at least a month ago. Beta 2 was seeded to developers on December 12th of last year. The iOS 5.1 beta is only for developers and can only be installed if you have developer access. Today, Apple just released iOS 5.1 beta 3 (build 9B5141a) to developers, which apparently fixes some bugs and improvements over the previous beta.
Currently, developers can only update to iOS 5.1 beta 3 via Over-The-Air updates, but it should soon be available for download from the Apple iOS Dev Center. We are not sure what other hidden code or features can be revealed from this update, we will keep you updated. If you remember, beta 2 revealed some information on the use of quad core processors in next generation Apple devices.
If you find something new, do let us know through the comments.
Update #1: Early testers are reporting that the Toggle to turn off 3G is back in beta 3.
Update #2: iOS 5.1 beta 3 is now available in the Apple iOS Dev Center.