Apple has begun seeding iOS 5.1 Beta 3 to developers over software update.

The new version is build 9B5141a and is a 76.3 MB update. It's not yet available through the iOS dev center but it should be soon.

The release notes for iOS 5.1 Beta 3 have now been posted, and one item of note involves a new API to help developers flag app content that should not be backed up.

"iOS 5.1 introduces a new API to mark files or directories that should not be backed up. For NSURL objects, add the NSURLIsExcludedFromBackupKey attribute to prevent the corresponding file from being backed up."

One feature of the new iOS 5.1 Beta 3 build has been discovered, that it brings back the ability to turn off 3G. 3G offers faster data speeds but uses more battery power than EDGE, so the switch would help users save quite some battery life.

We'll let you know if anything new is found in the firmware.

via iclarified via MacRumors