Interestingly, the reason for the limitation of mmWave 5G to the largest iPhone is said to be a simple case of size and power capabilities, with the iPhone 12 Pro Max the only one that can provide what mmWave radios need.
Fast Company also notes that not all iPhone 12 Pro Max handsets will support mmWave, too. Those in the United States, Korea, and Japan will be the blessed iPhones. Everyone else will have to settle for the slower sub-6Ghz 5G instead.
The source says only the largest phone in the line has room inside for the special antenna design required for millimeter wave and larger battery needed to accommodate millimeter wave’s significant power draw. Also, only the U.S., Korea, and Japan versions of the Pro Max will support millimeter-wave 5G.
At this point it’s difficult to tell whether any of this news really matters, however. 5G is still very much in its infancy and few people would be able to enjoy mmWave 5G speeds, at least now. Things will likely change in the future however, and anyone keeping an iPhone for multiple years might suffer from the lack of mmWave 5G connectivity.
Apple is expected to announce all of its 2020 iPhones soon enough so we’ll get the answers to all of our questions then.