of the iPhone 4g prototype leaked to Gizmodo seem to be of an early production model rather than an early prototype. The way the matter has been reported, which has been to knife Gizmodo for running the story rather than look at the information, missed some important features.
Apple didn't retract the claim that it was a true iPhone in fact wrote a semi-polite letter asking for it back. But when you come down to it, people didn't believe the phone was real because it did not look nice. It seems too practical and has none of the design over substance that Apple is famous for. It looked like a prototype, not a replacement.
However John Gruber at Daring Fireball had a look at the barcode numbers
which seem to indicate that the Gizmodo phone is closer to being a final production unit. He said that the barcodes attached to the unit read ‘N90_DVT_GE4X_0493’. “N90” is Apple’s codename for the fourth-generation GSM iPhone, slated for release this June or July. ‘DVT’ stands for ‘design verification test’, an Apple production milestone. The DVT milestone is very late in the game.”
He said the fact it was dropped by an engineer indicates that the phone is at a level where it needs to leave the Apple campus for accurate mobile phone testing. There are likely several next generation iPhones in use around Cupertino as part of the testing.