It’s possible that Apple could be testing the iPhone OS version 3.1.3 and version 4.0, which we assume would run on the new iPhone3,1 device being currently tested. The rumours have come from server logs showing the new versions of the OS.
The BoyGeniusReport found evidence of two new user agents in their log files. The first, iPhone OS 3.1.3 would be a minor bug fix. The second, iPhone OS 4.0 would be a significant upgrade to the operating system.
The user agents could be faked, but it’s likely by now that Apple are testing these versions of the OS.