Only after the thrill of picking out your new smart phone is over--after you’ve marveled at all the stylish new gadgetry and features, signed a service contract and finally laid your money down--do you finally get a feel for the speed and reliability of the wireless service that connects your new phone. That wireless service--so often an afterthought to smart phone buyers--is hugely important: it connects your new phone to all the fun and useful apps and services that made you lust after a smart phone in the first place.

The truth is, the 3G wireless networks of today are not perfect (they are, collectively, a work in progress), and they are not all created equal.

Because independent research on these networks is very hard to come by, PC World took a single-day, real-world snapshot of the performance of the three biggest 3G networks in the U.S. – Verizon Wireless, AT&T and Sprint – using industry-accepted testing technology and techniques. If there’s a smart phone in your future, we hope to give you some idea of the wireless service that may be in store for you, beyond the anecdotal information you hear from other users, on the web and in the media, and aside from the claims made by the wireless service providers themselves.

Now for an important note before we start reviewing our results. Wireless signal, by its nature, is extremely variable; that is, many things, such as obstruction by fixed objects (buildings, trees, etc.), weather, network load, cell tower locations, and time of day, can affect the quality of the signal. These factors can cause service from a single wireless service to vary widely from day to day and from neighborhood to neighborhood. Our results, taken together, provide a snapshot of the performance of the largest 3G networks in 13 major markets during March and early April. But they are by no means exhaustive, and your own connection speeds may differ from ours. Please tell us about your own experience here.

Results: Speed and Reliability Testing by City: Click on the chart thumbnail at left to see the detailed results of our testing in 13 cities. The cities are listed in the left-most column; from that column you can move rightward across the chart to read first Verizon's, then Sprint's, and then AT&T's download and upload speed averages for each city. The "reliability" score is the percentage of our tests in which the service maintained an uninterrupted connection at a reasonable speed (faster than dial-up).

During March and early April, our testing partner, Novarum Inc., used Ixia ixChariot testing software to measure network performance from more than twenty fixed locations in each of the following cities: Baltimore, Boston, Chicago, Denver, New Orleans, New York City, Orlando (Florida), Phoenix, Portland (Oregon), San Diego, San Francisco, San Jose, and Seattle. In all, our testing partner ran 5443 individual tests from 283 testing locations. At each location, Novarum measured download speed, upload speed, and reliability for each provider's 3G service. (See "How We Tested and What the Ratings Mean.")

The Speed Numbers in Action: What do the speed numbers mean in real time, in the real world? The chart at left tells you how long it takes to download various common file types using various download speeds--from slow (2G) to fast (4G).

Testing Results in a Nutshell

In Novarum's tests for us, Verizon Wireless demonstrated a good mix of speed and reliability. Across more than 20 testing locations in each of the 13 cities we tested, Verizon had an average download speed of 951 kbps. Verizon demonstrated good reliability, too; the network was available at a reasonable and uninterrupted speed in 89.8 percent of our tests.

Sprint's 3G network delivered a solid connection in 90.5 percent of our 13-city tests. Sprint's average download speed of 808 kbps across 13 cities wasn't flashy (at that speed, a 1MB file downloads in 10 seconds), but dependability is an important asset. The Sprint network performed especially well, both in speed and in reliability, in our test cities in the western part of the United States.

The AT&T network's 13-city average download speed in our tests was 812 kbps. Its average upload speed was 660 kbps. Reliability was an issue in our experience of the AT&T system: Our testers were able to make a connection at a reasonable, uninterrupted speed in only 68 percent of their tests.

Somewhat surprisingly, our testers also found that the "bars of service" readings on their phones were rarely an accurate predictor of the quality of the ensuing connection. In most places and with most wireless providers, the "bars" did little more than indicate whether the phone had access to some service or to no service. (See "What Do Bars Say About Your Connection?")

Please tell us about your own wireless broadband service experience here .