Update: The device originally listed has since been pulled from eBay. However, another model listed as a "genuine prototype" and with a white paint job is also available.
The new listing from seller "jtmaxo" was set to expire on July 11. The posting referred to the device as a "prototype," and notes that the serial number written on it is not valid when entered on Apple's website.
The device has "DF1692" etched in the bottom right corner. According to This is my next, that unique code is meant to allow Apple to keep track of what prototype hardware belongs to a certain employee.
"We're hearing through the grapevine that this particular unit has hardware similar to Gizmodo's prototype last year -- not identical to the retail version internally, though we don't know exactly what has changed," the report said.
It was a different prototype iPhone 4 that was obtained and shown off last April. Gizmodo got their hands on the hardware after a third party obtained the pre-release device at a California bar.
That unit was being tested by an Apple software engineer, and the device was encased in a plastic case intended to disguise it and make it look like a previous-generation iPhone 3GS. The source of the latest prototype posted on eBay is unknown.
The seller said that the phone has some signs of wear, and it will not activate via iTunes with the AT&T network when plugged into a computer. iTunes presents an error suggesting that the user visit their nearest AT&T or Apple retail store.
On the back side, the model number, FCC ID storage and other information displayed on the prototype iPhone are replaced with Xs. The volume buttons also do not have the usual "+" and "-" symbols, though the rest of the device has a similar external appearance to the final iPhone 4 that was eventually released last June.