Inside iPhone 4S US mobile data: AT&T vs Sprint vs Verizon
AT&T is indeed the fastest phone network
Apple's originally exclusive iPhone partner, AT&T, is clearly the fastest US mobile network. That's largely due to the fact that AT&T's GSM/UMTS network takes advantage of the iPhone's ability to support AT&T's newest UMTS network technologies: High-Speed Uplink Packet Access Category 6 (supporting data uploads of up to 5.76 Mbps on iPhone 4 and 4S), and High-Speed Downlink Packet Access Release 5 (enabling data downloads of up to 14.2 Mbps on the iPhone 4S or up to 7.2 on the iPhone 4 and 3GS).
AT&T doesn't come close to saturating the iPhone's data capabilities; the best download we observed in testing was 5.4 Mbps, and the best upload was 1.2 Mbps. But those speeds are comfortably fast, comparable to accessing WiFi from a mobile device. For data downloads, AT&T's top speed was more than twice as fast as the best scores obtained on Sprint or Verizon, although AT&T's fastest uploads were largely comparable with the best uploads found on Sprint or Verizon.
Whether you're using Maps or Siri or watching videos, AT&T provides hands down faster experiences, at least when you have good service. Whenever you don't have AT&T's best service coverage, speeds drop considerably, even falling to zero in some places. However, on average across all the tests performed in parallel in both rural and urban settings across California, AT&T averaged 1.623 Mbps down and 0.764 Mbps up, numbers than were more than twice as fast overall compared to Verizon's downloads (averaging 0.724 Mbps) and 2.9 times as fast as Sprint's download average (0.559 Mbps).
In terms of upload speeds, AT&T's average was about a third faster than Verizon's average upload speed of 0.557 Mbps, and 1.8 times faster than Sprint's, which clocked in at 0.422 Mbps. If you want the fastest mobile service for your iPhone, AT&T is the clear winner, even when you figure in areas of weaker coverage.
AT&T also has the greatest potential for building on its 3G speed lead for iPhone users. Verizon and Sprint are tied to CDMA EV-DO for their 3G service, and those networks can't get much faster (although they could be make more reliable, potentially raising their average speeds closer to the technology's theoretical maximum of 3.1 Mbps down and 1.8 Mbps up).
AT&T is already delivering download speeds quite a bit faster than EV-DO is capable of ever achieving. On top of that, AT&T's network and the iPhone 4S are capable of even faster speeds up towards the theoretical 14.4 Mbps, something that Sprint and Verizon simply can't achieve with their existing 3G networks. That's why both Verizon and Sprint are working to build out LTE networks capable of faster speeds (although those networks won't ever benefit existing iPhone users unless they begin using an external MiFi wireless LTE device to relay WiFi data service).
Bottom line: AT&T is already fastest in general, significantly faster on average, and has far more room to grow in progressively rolling out even faster speeds to existing iPhone users over the next couple years.
Verizon coverage is indeed more widely available
Neither the average speed of AT&T's network nor its fastest peaks will matter to you, however, if you routinely want your iPhone to work in areas where AT&T delivers poor coverage. For example, we found specific locations where an AT&T iPhone simply wouldn't ring or get any service: at home, in most of the mezzanine level of the San Francisco Muni Metro, in parts of the forest headed to Lake Tahoe, and in the shadowed valley of Los Angeles' Runyon Canyon Park.
There are plenty of areas where mobile phones of all types fail to find service, but both AT&T and Sprint seemed more likely to lose coverage in certain dubious fringe areas than our Verizon test phone. Even in areas where one might expect not to have data coverage (such as in an underground metro station) the Verizon iPhone could often find enough service to remain marginally usable. These cases provide reasons why you might opt for slower overall coverage in order to have at least minimally functional service more of the time.
Having switched to Verizon in San Francisco earlier this year (as soon as the Verizon iPhone 4 became available), I have to report far fewer occasions where I discovered having no service at all, compared to AT&T. However, Verizon's data service is noticeably slower (particularly evident when loading maps) and belying its heavily promoted "better 3G coverage" rhetoric it seems to drop from 3G EVDO to "o" service (apparently 2G CDMA2000 1x, which feels significantly slower than AT&T's EDGE) surprisingly often. Driving across the country this summer I noticed Verizon losing service completely in some rural areas. Overall however, Verizon has demonstrated functional service in more areas than AT&T, 3G or not.
The decision to pick Verizon over AT&T therefore depends upon how much of your mobile experience occurs in areas with reliable AT&T's coverage. If you travel through lots of rural areas or know of poor coverage by AT&T in or around your home, office or school, you might likely be better off with Verizon's slower but in many cases more dependable service coverage.
At the same time, AT&T is incrementally improving its coverage map. Additionally, Apple's new iMessage and FaceTime capabilities means that you can now contact people and receive texts from other iOS 5 users even if you don't have good mobile service, if you are located somewhere that WiFi is available. Previously, if you didn't have mobile coverage, you couldn't send or receive any texts at all. That makes WiFi availability a secondary consideration when deciding whether to opt for AT&T's faster coverage or Verizon's often better coverage at slower data rates.
On page3 of 3: Sprint is indeed the only unlimited iPhone data contract still available, US iPhone carrier overview.