In the lucrative and competitive world of smartphones, Apple’s iPhone is the most popular device and Google’s Android—used by phone makers like Samsung and Motorola—is the most widely used operating system. With Palm gone, and the BlackBerry staggering, most smartphone buyers and app developers now think of it as a two-horse race.

However, Microsoft and Nokia, two former thoroughbreds of the smartphone market in the days before the iPhone changed the game, are determined to change that. They’ve teamed up in the hope of offering an appealing third choice. So far, Microsoft’s Windows Phone operating system has struggled to attract either buyers or app developers. But on April 8, Nokia and AT&T will begin selling the first high-end, 4G LTE, Windows Phone model released in the U.S., the Lumia 900.

The Lumia 900 looks rather different from other smartphones. It’s a solid, sturdy, single slab of rounded blue plastic—yes, blue—with a large, thin, bright screen that appears to lie on top, instead of being inset. (For the less adventurous, it also comes in black, and, in a few weeks, white.)

Plus, for an unspecified “limited time,” it costs just $100, half the typical $200 price of most other top-of-the-line competitors. That price requires a two-year AT&T contract whose fees start at $80 a month for a very minimal amount of data and voice minutes, plus unlimited texting. (It’s $60 without the texting plan.)

I’ve been testing the Lumia 900 and found that it provides the best home yet for the attractive Windows Phone software, but still doesn’t measure up to rival smartphones.





The Lumia 900’s screen is much larger than the iPhone’s, but the phone isn’t as big and bulky as some recent Android models. The Lumia 900’s screen is much larger than the iPhone’s, but the phone isn’t as big and bulky as some recent Android models.

The screen is a roomy 4.3 inches—much larger than the iPhone’s—but the phone itself, while larger than an iPhone, isn’t as big and bulky as some recent Android models. I found it comfortable in the hand and the pocket.

When on an LTE network, the phone delivered download speeds of between 10 and 15 megabits per second in my tests, faster than most home Internet connections. Voice calls were clear and reliable, and the rear camera delivers 8 megapixel resolution.

Also, the Lumia 900 features the three biggest advantages of the Windows Phone platform—a handsome, distinctive, tile-based user interface; a mobile version of Microsoft’s Xbox Live gaming network; and a mobile version of genuine Microsoft Office, which allows you to edit documents and share them with PCs and Macs, or store them in the cloud.

But, overall, I consider the Lumia 900 a mixed bag. Unless you are a big Windows Phone fan, or don’t want to spend more than $100 upfront, I can’t recommend the Lumia 900 over the iPhone 4S, or a first-rate Android phone like Samsung’s Galaxy S II series.

I was underwhelmed by the battery life, the browser, and the quality of its photos.

Plus, the Windows Phone platform has only a fraction of the third-party apps available for its rivals—about 70,000, versus nearly 600,000 for the iPhone and more than 450,000 for Android.

It also has a weaker content ecosystem. For instance, there is no way to buy TV shows or movies directly from the phone, and far fewer magazine and newspaper apps are available.

And if LTE—which I consider the only true 4G network in the U.S.—matters to you, bear in mind that AT&T offers that service in just 31 markets, versus 203 for Verizon. In most places, the Lumia, like other AT&T phones, including the AT&T version of the iPhone, delivers a slower version of 4G, which is really just a souped-up version of 3G.

The Windows Phone software itself on this new phone hasn’t changed. Instead of multiple pages of icons, as on iPhone and Android, it offers a scroll of tiles that show information. And it still has “hubs” that combine information like contacts and social-media updates for people you know.

Still, despite its flaws, including the likelihood of a lot of scrolling to get to apps, it remains a refreshing change from the dominant competitors.

My biggest problem was with the Web browser, a mobile version of Internet Explorer.

Back in January, when I tested the same browser on an entry-level Nokia Windows Phone, it worked fine on both the cellular network and on my Wi-Fi network. But the Lumia 900 stalled frequently when rendering websites on my fast, home Wi-Fi network, though the phone did fine on LTE.

To make sure my Wi-Fi wasn’t faulty, I tried some of the same sites, in the same spot, on an iPhone, an Android phone and even an older Samsung Windows Phone. All worked perfectly. Nokia had no explanation for this problem.

I found that, in light use, the battery lasted through a typical day. But in heavier use, including lots of email usage and Web browsing, streaming a one-hour TV show via Netflix, and conducting an hour-long phone call, the battery drained more quickly and was almost gone by late in the afternoon. This was especially true if I was using LTE much of the time.

While the Lumia 900’s processor is single-core, not the common dual-core found on other high-end phones, I found the phone worked smoothly and quickly, and played videos fine.

The screen resolution of 800 by 480 is lower than the iPhone’s, and I found the display generally less sharp than the Apple’s. The screen visibility was a bit better outdoors than most other phones I’ve tested, but not dramatically so.

The camera, despite having the same resolution as the new iPhone, took notably worse pictures of the same scenes in my tests. To my eye, colors were oversaturated, and details were less sharp.

There were a few other issues. The Mac version of Microsoft’s Windows Phone syncing software wouldn’t recognize the Lumia 900, though the PC version did. The on-off button isn’t labeled, or easily distinguishable, from the dedicated camera button.

Bottom line: If you’re looking for a $100, high-end smartphone, or are a Windows Phone fan who has been waiting for better hardware, the Lumia 900 is worth considering. But the phone had just too many drawbacks in my tests to best its chief competitors.

Write to Walt at walt.mossberg@wsj.com