Citing sources, some of those prototypes may have a new design centered around a curved screen.
The technology that would enable that curved screen is called OLED, which is a newer kind of display that has deeper blacks and lower power consumption.
The fact that Apple will need tens of millions of these OLED screens for next year is setting off a race among screen makers, including Samsung, LG Display, Foxconn-owned Sharp, and Japan Display.
The WSJ says that Samsung will supply "most" of Apple's initial OLED needs, confirming what Bloomberg reported earlier.
But Apple is pushing the other three to gear up to supply OLED iPhone screens as soon as 2018. That would require significant investment - the Journal says that Sharp would need to spend more than $5 billion to develop the technology and capacity to supply OLED screens to Apple.
"We don't know whether Apple's OLED iPhones will be a hit, but if Apple doesn't walk down this path and transform itself, there will be no innovation. It is a crisis but it is also an opportunity," Sharp chief executive Tai Jeng-wu said last month.
A clear picture
The information in Monday's Journal story lines up with other reports from Nikkei, as well as analyst reports from Barclays and KGI Securities.
As iPhone sales decline, pressure is mounting on Apple to deliver a very desirable new iPhone model in 2017 to return the line to growth.
This model is widely expected to feature glass casing, wireless charging, and a new edge-to-edge screen design, in addition to the latest chips and technologies.
"iPhone 8 design didn't sound 100% locked down but we believe the move is to a bezel-less design with screen sizes getting larger and curved edges in the original envelope," Barclays analysts wrote in November.
KGI Securities pointed to three iPhone models in 2017, with only one sporting the new kind of OLED screen. "We predict three new iPhone models will be launched in 2017: 5.1-5.2" OLED, 4.7" TFT-LCD, and 5.5" TFT-LCD," the KGI Securities analyst wrote.
The Journal warns that the OLED iPhone could be scrapped before its expected launch next fall. After all, Apple is testing 10 prototypes and reportedly killed an iPhone model months before launch in 2016. It sounds like what Apple ends up launching will depend on whether Apple's Asian suppliers can provide enough next-generation screens.