Amidst the hype surrounding Apple's latest smartphone, it's easy to forget what makes the iPhone so popular in the first place. But pick one up, and it's easy to remember: It's the gorgeous, industrial design, killer display, easy-to-use OS, and unbeatable app experience. And now, with the arrival of the iPhone 4S, Apple has finally worked out the calling kinks that plagued its devices in the past.

This time around, the iPhone 4S is available on AT&T, Sprint, and Verizon. AT&T's model is the best of the three. On AT&T you get support for simultaneous voice and data, as well as faster 3G speeds via AT&T's HSPA+ 14.4 network. So why are we rating this phone lower on AT&T than on Sprint? Because AT&T is making a much more aggressive push towards 4G LTE than Sprint is, and the iPhone 4S is not a 4G device.

(Sprint has an existing 4G WiMAX network, but at the moment that carrier's 4G strategy is muddled, as it's in the midst of transitioning between two technologies. AT&T's path is much clearer.)

Cellular Radio and Call Quality

See our review of the iPhone 4S on Sprint ($199.99 - $849.99, 4.5 stars) for a detailed look at the phone's hardware, software, and new features. Here we're going to focus on what makes the AT&T phone different, and how it performs on AT&T's network.

RF reception on the 4S was on par with the Samsung Galaxy S II Skyrocket ($149.99, 4.5 stars) and other top AT&T phones. Call quality on AT&T's network was also very good. Voices sounded loud, full, and natural in the phone's earpiece. Calls made with the phone sounded a bit thin, but still loud and clear, and background noise cancellation works very well. Transmissions through the speakerphone are also clear, and fine for indoor use, but not loud enough to use outdoors.

The 4S switches between its top and bottom antennas depending on which one is receiving better signal, which means it'll ignore whichever one you're covering with your hands. This design killed the "death grip" problem on the Sprint model, and it does the same here. By holding the phone in a strange, two-handed grip I was able to lower data speeds, but it wasn't significant, and it wasn't the kind of grip anyone would ever use to hold or talk on a phone.

The iPhone 4S also delivers on Apple's promise of longer battery life. I got 9 hours, 6 minutes of talk time with a strong 3G signal.

Data Speeds and Conclusions

Judging from the results we collected earlier this year in our testing for the Fastest Mobile Networks, we found that AT&T has the fastest 3G network in the U.S. That means the iPhone 4S, a 3G device, should be faster on AT&T than it is on Sprint or Verizon.

In my tests, the 4S on AT&T easily beat the same model on Verizon. The AT&T device averaged 3Mbps down and 1Mbps up, while the Verizon phone averaged a much lower .8Mbps down and .5Mbps up. The iPhone 4S, which uses an HSPA+ 14.4 modem, is also a lot faster than the iPhone 4, which has a slower HSPA 7.2 modem. In the same series of tests, the iPhone 4 on AT&T ($99.99, 4.5 stars) averaged 1Mbps down and .4Mbps up.

The iPhone 4S is also a good HSPA device in general. Speeds were comparable to those on a Samsung Infuse 4G ($24.99, 3.5 starts), which has an even faster HSPA+ 21 modem. The iPhone 4S on AT&T is also capable of simultaneous voice and data, which is unavailable on 3G phones on Sprint and Verizon.

But the 4S doesn't take the best advantage of AT&T's network. The phone's HSPA+ 14.4 modem works well, but the phone should have an HSPA+ 21 modem to get the best speeds on this network. AT&T also recently started to deploy its 4G LTE network, which is currently available in 15 U.S. cities, and the carrier expects to reach 70 million users by the end of the year. Right now, there are three phones that support it: the HTC Vivid ($99.99, 4 stars), Samsung Galaxy S II Skyrocket, and LG Nitro HD ($149.99, 4.5 stars). AT&T is anticipated to announce more LTE phones at CES in a few weeks. If you're buying a top-of-the-line smartphone you intend to keep for two years, it should be future-oriented.

LTE is far faster than HSPA+. In a number of head-to-head speed tests, the Nitro averaged 16.5Mbps down and 4.5Mbps up, while the Skyrocket averaged 15.4Mbps down and 3.9Mbps up. Keep in mind, those tests were conducted at the same time and place as the speed tests on the 4S, which pulled in 3Mbps down and 1Mbps up.

The ads are true: Apple's iPhone 4S for AT&T really is "the most amazing iPhone yet." It's an excellent device, and 4G or not, it's still going to be the right choice for many AT&T users. But if you're looking for the fastest, most powerful smartphone right now, then you should be looking for a 4G LTE device like the Samsung Skyrocket or the LG Nitro HD.

Benchmarks

Continuous talk time: 9 hours 5 minutes

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