iOS 5 is expected to bring with it some juicy new features, not least a new notification system and application developers are starting to see the next iOS version show up in the stats they receive from Apple. Proof the company is ramping up testing, perhaps?
The photo from 9to5Mac shows the OS is being tested on all kinds of devices including iPods, iPads and iPhones of all versions including the iPhone 3GS (not shown in the picture). It was assumed the ageing 3GS would be left out of future major iOS releases but apparently Apple are at least testing the combination. Whether that will culminate in the handset being updated though remains to be seen.