We've run tests, and it looks like AT&T is capping upload speeds for several devices that aren't the iPhone 4.

It recently came to PCMag's attention that AT&T may be capping upload speeds on many devicesto speeds far lower than its network can support. This may be the case for many devices on AT&T other than the .

We saw evidence of this recently when testing AT&T's latest round of USB modems, the and the . In many parts of NYC, both devices showed upload speeds far below their capabilities. It seems that AT&T devices that should support HSUPA (which should enable uploads up to 1Mbps, according to our past modem tests) are being limited to UMTS (maxing out at 384kbps), which is less than half that speed.

Originally alerted by reader Zack Nebbaki, we ran some head-to-head tests in the PCMag Labs to see just how the numbers stacked up.

We tested an , a , and an Apple iPhone 4. The Inspire and the Atrix are supposed to be faster than the iPhone overall, as both devices use HSPA+ 14.4 modems while the iPhone has an HSPA 7.2 modem.

We used Ookla's SpeedTest app and connected each phone to the same server, then ran the test six times. As you can see in the chart below, we got UMTS (not HSUPA) upload speeds on the Inspire 4G and the Atrix each time. Tests done with the iPhone 4 at the same time, in the same location, showed dramatically higher upload speeds. This correlates with our results for the two USB modems we tested recently.

These results suggest that AT&T is, in fact, capping upload speeds for at least several different non-iPhone 4 devices. Now, we haven't worked out the variables here. This could be a problem specifically with the four devices we've tested (the two phones plus the Adrenaline and Shockwave USB modems), or a problem that specifically only affects certain parts of New York City.

We contacted AT&T and asked if it is capping upload speeds to UMTS levels, and if so, where this is being done and for how long. We also asked why the iPhone is getting faster speeds than the other devices.

AT&T was evasive, saying, "As you noticed, we have a number of HSUPA devices today and we will have more HSUPA-enabled devices in the futurenew devices and updates to existing models."

Please note that AT&T's comment does not appear to be a denial of anything in this article.