Take a look at the P20 Pro and there's a good chance you'll wonder how Huawei managed to stuff three rear cameras into a phone roughly the same size as its two-cam rivals. Thankfully, it's no longer much of a mystery. The DIY repair crew at iFixit has torn down the P20 Pro to explain how Huawei pulled off the design. The primary, monochrome and telephoto cameras are all stuffed into a compact module that's closely connected to a similarly space-efficient mainboard -- in fact, it looks like there was plenty of room for the 4,000mAh battery and speakers (though there's no headphone jack, alas).
The enclosures for the cameras suggest to iFixit that all three might have optical image stabilization, not just the telephoto module as Huawei claims (the other two sensors use software). However, it's not certain that this is the case, or that they're active even if the hardware is present. We've asked Huawei if it can clarify the situation.
The one certainty: you probably won't be fixing the P20 Pro yourself. Many of the components are modular and thus easier to replace (as with the Galaxy S9), but you have to disassemble a significant chunk of the phone to replace the screen. The battery requires some effort, too, and the glass back doesn't help matters. This is yet another case where clever internal packaging comes at the expense of repairability.