We sent the intrepid Ryan Salerno across 20 NY blocks armed with an iPhone 3GS and an iPhone 4. He ran speed tests along the way, ferreting out any oddities. Downloads? Exactly the same. Uploads? An order of magnitude faster.
Let's take a quick step back. In terms of downloads, the iPhone 3GS and iPhone 4 trade blows like boxers, each besting one another in speeds here and there—without* any sure rhyme or reason. In other words, the results look typical. Depending on their exact proximity to various towers and buildings, one phone or the other could squeeze a bit more out of their radio transceiver.
However, when you look at uploading, the differences are striking. In our tests, iPhone 4 averaged uploads that were 10.8X times faster than the 3G. Given the distance traveled, that's beyond the limitations of any single tower or connection, and a bit beyond any simple explanation we have as well (processor speed and RAM, for instance, might explain some speed boost but probably not this much).
UPDATE: Yes, duh, it's due to the HSUPA chipset, which was lacking in the iPhone 3GS.
We tested our iPhones in other locations, Chicago and San Francisco, comparing 3G and 3GS models to iPhone 4. We found that, while the iPhone 4 wasn't always 10x faster, it was consistently at least 5x faster.
I guess it's safe to say, the iPhone 4 may not be any faster for downloads, but for uploading pictures and videos? We'll all see huge improvements. And yes, all thanks to HSUPA, what's clearly the least recognized, best new feature in the iPhone 4.
*It's worth noting, to control for any radio antenna issues, all testing was done with the iPhones sitting on a flat surface.
Additional reporting by Don Nguyen.
Additionally, on a basic Wi-Fi test, we saw some differences in both down and upload on 2.4GHz G. Of course you have to keep in mind that when it comes to Wi-Fi performance on a mobile device, range is typically more important than raw speed. But despite the fact that wireless speed on a mobile device is not the main thing to focus on, its nice to see the speeds go up rather than say same.