Apple has seeded iOS 5.1 beta to developers and it hasn't taken some long to discover references to next-generation iPhones and iPads within it.

References to an iPhone 5,1 and an iPad 3,2 as well as an iPad 3,3 were noticed by Filippo Bigarella, reports Apple Insider, as well as a reference to an iPad 2,4.

While current second-generation models are referred to as iPad 2,1, iPad 2,2 and iPad 2,3 within iOS, iPad 2,4 has not been spotted for, with some speculating that it could refer to an iPad that will be compatible with US network carrier Sprint's CDMA network.

Another interesting point to note about iOS 5.1 beta is that it isn't available over the air - as future iOS updates will be - but must be downloaded from Apple's developer site instead.

The developer build is coded 9B5117b and once installed cannot be rolled back to previous versions of iOS, Apple warned.

Apple also released a preview version of Xcode 4.3 alongside the iOS 5.1 beta.