iOS 5.1 beta 3 has been released to developers today, the latest build is 9B5141a and is available as a fairly small over-the-air delta update to those currently running iOS 5.1 beta 2. As past iOS 5.1 betas have shown, compatibility is with iPad 2, iPad, iPhone 4S, iPhone 4, iPhone 3GS, and iPod touch 3rd and 4th generations. Registered iOS developers should be able to get the latest build through the Apple Dev Center as well.

Not many new features are known, but reports indicate iOS 5.1 beta 3 gives iPhone 4S the ability to disable 3G and manually switch to the slower Edge network, something that currently isn’t possible on the 4S running iOS 5.0.1. While Edge is much slower, it’s better at conserving battery life and has a larger coverage area, particularly in rural locations.

The first beta of iOS 5.1 was made available on November 28, 2011, and the second beta on December 12, presumably the long holiday break contributed to the nearly four weeks between the release of the 2nd and 3rd betas, but either way we’re inching closer and closer to a public release soon.

Apple has released iOS 5.1 beta 2 to developers with a continued focus on bug fixes. A notable added feature however is the ability to delete photos from Photo Stream directly on the iOS device, as opposed to the current method of removing pictures from iCloud.

The build comes as 9B5127c and runs on the same hardware as the prior release: iPad, iPad 2, iPhone 4S, iPhone 4, iPhone 3GS, and iPod touch 3rd and 4th generations. Registered developers can grab the 800MB firmware updates directly from Apple’s iOS Developer Center, the update must be applied separately as no OTA option is available.

Alongside beta 2 of iOS 5.1 comes XCode 4.3 Developer Preview 2, and a new build of Apple TV 2 firmware that is intended for testing with iOS 5.1 beta devices.

If you’re interested in reading the release notes of iOS 5.1 beta 2, — has posted them.

iOS 5.1 beta 1 continues to spill the beans for Apple product ID’s, with the latest find being a direct reference to Apple’s next-generation iPhone, referenced as “iPhone 5,1″, and two unreleased iPad’s, referenced as “iPad3,2″ and “iPad3,3″.

iPhone5,1 would technically be the sixth generation iPhone, which may indicate iPhone 6 is the proper name for the device. Of course, nothing but speculation is known about the iPhone 5 (6?), but references appearing in current iOS 5.1 beta builds suggest there are working prototypes that are running iOS 5.1 right now in Cupertino. Most rumors suggest the next generation iPhone will have a 4″ screen, a thinner aluminum enclosure, and likely an A6 CPU, and a release time frame could be somewhere between summer and fall of 2012.

The iPhone 5,1 reference was first discovered by @Filippobiga on Twitter – you can follow us there too – who also pointed out the references to two unreleased iPad 3 models, also shown in the screenshot as iPad 3,2 and iPad 3,3. Presumably, those are for the upcoming iPad model that is expected to debut sometime in early 2012 with a retina display.

Apple has seeded iOS 5.1 beta 1 to developers, the build is 9B5117b and runs on iPhone 4S, iPhone 4, iPhone 3GS, iPad, iPad 2, and iPod touch 3rd and 4th gen. For those in the iOS developer program, you can download the iOS 5.1 beta right now directly from Apple’s dev center as IPSW files. Alongside the iOS 5.1 beta came a new build of Xcode 4.3, which is also required for developing anything for iOS 5.1.

The 5.1 beta notes include many mentions of bugs, you can read the full release notes on 9to5mac if you’re interested. They also uncovered references to an unreleased iPad 2 model in the beta, which they presume is for the Sprint network.