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It was recently revealed that the iPhone 17 is Apple's most popular lineup of all time, and the iPhone 17 Pro and 17 Pro Max sit at the very top of that lineup. Yet, those who have looked closely at the U.S. models have also been puzzled by a mysterious plastic strip at the phone's uppermost section. This strip is on the top edge of the phone, not far from where the power button used to be on the iPhone 5s and earlier. It really stands out on the all-aluminum body and certainly appears as if it's hiding some sort of hidden feature.

Many users correctly guessed the function, as it turns out that the strip on the top of the iPhone 17 Pro is just a window for a 5G mmWave antenna. Surprisingly, the slit is missing on models outside of select markets. This is because the antenna is only needed in regions that rely on mmWave, like North America, for high-speed 5G internet.

Though that solves the main mystery, other questions remain: Why didn't previous models have the antenna in that position? Why did Apple change the design? Well, it all boils down to the fancy new all-aluminum body that iPhone 17 Pro reviews praise. Aluminum impedes radio signals, so the slit was very likely a necessity.

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Without the strip at the top of the iPhone 17 Pro (made of an RF-transparent material), users would probably complain about the poor 5G speeds in urban areas. As a standard in the United States, mmWave 5G has been a consistent addition to U.S. iPhone models as far back as the iPhone 12. How did those models handle the antenna, though?

It depends, and it's quite interesting. On the iPhone 12 Pro, for instance, the slit was located below the power button. This changed for the iPhone 14, where Apple moved the slit to the top of the phone's right side. On the next-generation Pro model, the slit was located slightly higher. The iPhone 16 Pro had the antenna in the upper part behind the back panel, probably to accommodate the new Camera Control button.

What about the base iPhone 17 model? As iPhone 17 reviews have pointed out, the phone sports an aluminum frame, though the back is made out of glass. Thus, a slit at the top would have been an unnecessary addition, and the antenna was simply tucked away behind the back panel. Either way, the newer strip at the top of the iPhone 17 Pro is a dead giveaway of a U.S. model. The clever bit of design may have puzzled users after the Pro model came out, but it's actually a good position for the mmWave 5G antenna. After all, you can't accidentally cover it with your finger while using the phone, right?