For millions of iPhone owners, or would-be iPhone owners, who dislike AT&T's wireless service or prefer Verizon Wireless service, liberation is at hand. Starting Feb. 10, Apple's iconic smart phone finally will be available in the U.S. on a second carrier, Verizon, instead of just on AT&T, which has been the exclusive iPhone network since the device launched in 2007. Current Verizon customers can pre-order the iPhone Thursday.  Walt Mossberg compares the new Verizon iPhone 4 to an AT&T iPhone 4, and finds that they aren't interchangeable. The Verizon has much better voice calls, he says, but there's a trade off in data speed.  Complaints about dropped voice calls, or calls that can't be initiated, on AT&T's service, especially on iPhones, have been legion. Meanwhile, Verizon has enjoyed a general reputation for reliable voice service. So, many frustrated AT&T iPhone users and those scared off by reports of dropped calls, or simply loyal to Verizon, have been eagerly anticipating this move. To these people, I'm here to say: Yes, there are some major benefits to having your iPhone on Verizon, but, as with all good things, there are also trade-offs.  I've been testing a Verizon iPhone 4 and comparing it to an AT&T iPhone 4, which has been out since last summer. The phones themselves are essentially identical, except for the fact that they have different radios inside to accommodate the two carriers' differing network technologies. They aren't interchangeable.  On the big question, I can say that, at least in the areas where I was using it, the Verizon model did much, much better with voice calls. In numerous tries over nine days, I had only three dropped calls on the Verizon unit, and those were all to one person who was using an AT&T iPhone in an especially bad area for AT&T: San Francisco. With the nearly identical AT&T model, I often get that many dropped calls in one day.  Calls on the Verizon unit were mostly crisp and clear, including speakerphone calls and those made over my car's Bluetooth connection. On my first full day of testing, I did have several Verizon calls that dropped out for a few seconds, before recovering. Apple attributed this to a very minor glitch I'd encountered in my initial setup of the phone and urged me to reboot it. I did and suffered no more momentary dropouts.  The Verizon model also introduces a feature that some iPhone power users have been craving but that AT&T hasn't allowed in the past: the ability to use the phone, for an extra monthly fee, as a Wi-Fi hot spot for Internet connectivity to multiple laptops or other devices. In my tests, this worked fine with Windows and Macintosh laptops, and an iPad. Wednesday afternoon, AT&T countered by announcing a similar Wi-Fi hot spot plan for the iPhone at an unspecified future date.  For an extra fee, Verizon iPhone users can use the phone as a Wi-Fi hot spot. AT&T has rushed to counter this feature with one of its own.  Also, Verizon is, for an unspecified but limited time, offering an unlimited $30 a month data plan for the iPhone. That is something AT&T once offered new customers, but has since replaced with capped plans offering fixed amounts of data at $15 or $25 a month. (Existing AT&T customers have been allowed to keep their $30 unlimited plans.)  What about the trade-offs? Chief among them is data speed. I performed scores of speed tests on the two phones, which I used primarily in Washington, and its Maryland and Virginia suburbs, and for part of one day at Chicago's O'Hare Airport. In these many tests, despite a few Verizon victories here and there, AT&T's network averaged 46% faster at download speeds and 24% faster at upload speeds. This speed difference was noticeable while doing tasks like downloading large numbers of emails, or waiting for complicated Web pages to load. AT&T's speeds varied more while Verizon's were more consistent, but overall, AT&T was more satisfying at cellular data.  Also, because Verizon's iPhone—like most other Verizon phones—doesn't work on the world-wide GSM mobile-phone standard, you can't use it in most countries outside the U.S. AT&T's iPhone does work on this standard, and can be used widely abroad, albeit at very high roaming rates. In the midst of my testing, I had to travel to Hong Kong, one of the few countries where the Verizon iPhone functions. But even there, it only worked for voice, not data, at least in the areas where I was working. The AT&T model handled both voice and data everywhere I tried it there.  Finally, the Verizon model can't fetch Internet data at the same time it is making a voice call, something the AT&T model can do. In fact, if you try to, say, call up a Web page while on a voice call with the Verizon model, you get an error message warning the two things can't be done simultaneously. While this distinction is a weapon in the war of words between the carriers, I doubt it's a big deal for most average users. My guess is that the most common things you'd want to check while talking would be your calendar, contacts and notes. And, in my tests, it was possible to check all those things on the Verizon model during calls, even though I have them set up to sync via the Internet.  I did have some issues with the Verizon model. In the D.C. area, long a coverage stronghold for Verizon, it kept switching briefly from 3G mode to slower 2G mode. This didn't affect voice quality, and didn't last long, but it slowed data downloads drastically for short periods. Also, on my first day of testing—after the setup glitch but before I rebooted—the Verizon phone showed poor battery life, and had trouble connecting to my car's Bluetooth setup. After that, these problems disappeared. Bluetooth worked fine and I was able to make it through a day with the battery on both phones.  Apple lists the specs on the two models as identical. They both start at $199, both have the same battery-life rating, both run the same operating software. In my tests, I was easily able to transfer all my apps, music, photos, settings, music and videos from the AT&T iPhone to the Verizon model, using iTunes, and I didn't run into any apps or media that failed to work as expected.  Prices for voice and data plans are a bit different. The least you can pay monthly for an iPhone on Verizon is $75, which includes 450 voice minutes, 250 text messages and unlimited data. On AT&T, you can pay just $65, but your data is limited to a paltry 200 megabytes, though you get 1,000 text messages in this scenario.  The Verizon wireless hot-spot plan costs $20 a month for 2 gigabytes of data, but gets expensive if you run over: $20 for each extra gigabyte.  One big question about the Verizon iPhone that neither company is answering is whether it will be updated to a new iPhone 5 model when the AT&T model is updated. Such updates typically have occurred in June or July, which could make people who buy a Verizon iPhone now resentful that their new phone was bested so soon. Of course, Verizon customers who wait might be resentful if their version of the iPhone isn't upgraded at the same time as AT&T's.  Officials at both Apple and Verizon will only say they don't intend to make Verizon customers unhappy, but that could mean anything.  Bottom line: In my tests, the new Verizon version of the iPhone did much better at voice calling than the AT&T version, and offers some attractive benefits, like unlimited data and a wireless hot-spot capability. But if you really care about data speed, or travel overseas, and AT&T service is tolerable in your area, you may want to stick with AT&T.
Walt Mossberg reviews the new Verizon service for the iPhone 4. Some major benefits include crisp, clear calls with relatively few drops. But AT&T offers faster data downloads.