There are two versions of the iPhone 7 -- and one is way slower

iPhone 7 vs. Galaxy S7: The underwater challenge
iPhone 7 vs. Galaxy S7: The underwater challenge

All iPhones may look the same, but under the hood it's a different story.

Some iPhone 7s use a Qualcomm modem, while others have an Intel modem. That distinction could make a difference in how fast an iPhone 7 Plus can send messages and load your favorite app. A new report from Cellular Insights found that the Qualcomm modem performed 30% better than Intel's. The researchers only tested the iPhone 7 Plus, but the two types of modems are also used in the iPhone 7.

Related: Is Apple trying to kill the iPhone's home button?

So how do you make sure you don't end up with the slower iPhone? If you have a Verizon (VZ), Sprint (S) or SIM-free model, you're in good hands, according to the Cellular Insights report. Another preventive measure is to make sure you buy your phone in the United States, China or Japan. Those are the only countries where the speedy Qualcomm version is sold.

Yet not every iPhone purchased in the U.S. has the faster modem. iPhones from T-Mobile, AT&T and Telstra include the Intel modem.

To determine if your iPhone has the Intel modem, check the model number, found in small print on the back of your smartphone. The Intel modem is in Model A1778 and Model A1784.

While the Intel modem is slower, it may not be slow enough to bother users. Cellular Insights ran comparison tests, showing that the Intel-powered iPhone 7 Plus was in the ballpark of the iPhone 6S in areas with poor reception.

It's unclear why Apple is offering iPhones with two different speeds. The company did not immediately respond to a request for comment. Some reports have suggested that by shifting some of its modem business to a Qualcomm (QCOM) competitor, Apple gains leverage to extract better prices from Qualcomm.

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