Windows Phone 7.5: What will make it a winner?

This much we know: The smartphone market has room for two wildly successful platforms.

I refer, of course, to Apple's iOS and Google's Android. Both are blockbusters, and I don't see any reason why they can't simultaneously thrive for years to come.

But is there room for a third major player?

At the moment, with WebOS undergoing an open-source reboot and RIM's next-generation BlackBerry OS apparently nowhere near completion, only one other phone platform has an immediate shot at being a contender: Microsoft's Windows Phone 7.5. It isn't there yet. In fact, Gartner's latest worldwide market-share numbers show Windows Phone capturing a piddling 1.5 percent of the market, behind five other rivals.

Still, the idea that Windows Phone might go from being an also-ran to a solid success doesn't feel like crazy talk. Recently, I popped the SIM card out of my iPhone 4S, put it in a Lumia 800 handset loaned to me by Nokia, and lived with Windows Phone 7.5 for over a week. I not only lived to tell the tale, but enjoyed doing so. In most respects that matter, Microsoft's mobile software is terrific.

And the experience got me thinking: What characteristics does a mobile operating system need to find success?

I came up with five factors:

Great software. Last year's Windows Phone 7 was tantalizing but decidedly unfinished. Windows Phone 7.5 is just plain pleasing--utterly original, easy to figure out, and both efficient and fun to use. In terms of overall pleasantness, it's iOS's most serious rival. (Google's Android 4.0 Ice Cream Sandwich is easily the best version of Android to date, but it still comes off as a nerdier, clunkier echo of iOS.)

Hardware that's at least as great. Here, Windows Phone could use some help: The current lineup of available phones is far from terrible, but it's also not anything to go gaga over. The Lumia is a gorgeous piece of industrial design, but I found its phone to be mediocre by current standards. Another Windows Phone 7.5 model I've used, HTC's Radar 4G, is a nice midrange phone, not a flagship. Samsung's Focus models come off as repurposed Galaxy S models.

I'd like to see somebody come up with a Windows-based device so sleek and capable that it leaves iPhone and Android owners jealous. I wouldn't be surprised to see Nokia pull it off: It's capable of building drool-worthy hardware.

Apps. Lots of them. iOS still has the most programs and the best programs. Android is giving Apple increasingly fierce competition. Both platforms have app selections that number in the hundreds of thousands.

And Windows Phone? Well, it certainly isn't floundering. After a little over a year, it's got 40,000 third-party apps to its name, which sounds like at least modest momentum to me.

Of course, Windows Phone doesn't just need lots of software; it needs the right software. So far, its roster of high-profile apps is spotty. It's got Netflix and Spotify, for instance, but not Hulu and Pandora. And during my time with the Lumia, my single biggest issue was that I missed photo-sharing gem Instagram, which remains an iPhone-only delight.

At this point, when I meet with a mobile app developer and learn that it plans to support Windows Phone, it still comes as a pleasant surprise. That needs to change.

Support from carriers. Most Americans buy their phones from AT&T, Sprint, T-Mobile, or Verizon Wireless. At the moment, AT&T has five Windows handsets, T-Mobile have two, and Sprint and Verizon have just one apiece. These companies don't necessarily need to stock gazillions of models--hey, the iPhone is available only in one new version and two older ones--but they need to go out of their way to tell shoppers what Windows Phone is and why they might prefer it over an iPhone or an Android handset. Wireless merchants don't have a fabulous track record, however, when it comes to handling products that require a bit of explanation.

Buzz. Windows Phone won't surge unless people get excited over it. The reviews, such as this one by my CNET colleague Jessica Dolcourt, are about as uniformly enthusiastic as tech-product evaluations get. And one survey showed that Windows Phone 7 owners were happy, or at least happier than Android users. But with Windows Phone sales so meager to date, there simply aren't enough consumers out there showing off their handsets to their buddies and raving about them.

I remain cautiously optimistic that Windows Phone will catch on. For one thing, Microsoft can afford to be patient with it--and the world's leading software company really can't afford to abandon the smartphone software market.

More important, Windows Phone 7.5 is a fine operating system that deserves to be successful. Sooner or later, good products usually do okay. If Windows Phone doesn't, it might be a sign that the dynamics of the smartphone business aren't going to let anything that isn't iOS or Android do well anytime soon. Correction at 8:02 p.m. PT: The story previously misstated the number of Windows Phones available on AT&T and Sprint. The updated story contains the correct figure.