The first of these devices will be an upgraded version of the current iPhone X. Given that the iPhone X's design was all-new, don't expect any major changes on that front. However, Apple could very well add in a faster [hypothetical] A12 processor, 4GB of RAM (up from 3GB on the current model) and further tweaks to the rear cameras and the Face ID biometric authentication system. Expect the smartphone to retain the 5.8-inch OLED display that was first introduced last year along with its controversial "notched" design.
The biggest of these new phones will be a so-called iPhone X Plus, which will have a display measuring 6.5-inch diagonally. If you recall, we saw an alleged leaked image of the display assembly for this device over the weekend. According to Bloomberg, this device would be aimed particularly at business users and could cannibalize iPad Mini sales.
The third new iPhone model would be a cheaper variant of the iPhone X. While it would retain the 5.8-inch edge-to-edge display of the iPhone X, it will instead rely on cheaper LCD technology rather than OLED. In place of the premium-feeling stainless steel frame that adorns the iPhone X, the cheaper model will reportedly features an aluminum frame while retaining the glass back (to support wireless charging).
It's reported that Face ID will be supported on all three iPhone models to be introduced in 2018.