Chinese labour report references less expensive iPhone production

It's nowhere nearly like leaving a prototype in a bar, but if proven accurate, a Chinese labor report potentially leaking information about an announced, less expensive iPhone, certainly won't make Apple happy. First noticed by Jony Evans of Computer World, the report includes:

"Today’s work is to paste protective film on the iPhone’s plastic back cover to prevent it from being scratched on assembly lines. This iPhone model with a plastic cover will soon be released on the market by Apple."

Ben Lovejoy of 9to5Mac noticed this line:

Its assembled products include iPhone 4, iPhone 4s, iPhone 5, and low-priced plastic iPhones

The iPhone 3GS was discontinued when the iPhone 4 went free last year, which means Apple is not longer ordering any known plastic-backed iPhones. So, what product are they referencing?

Source: Computer World, 9to5Mac