More than 50% of all Americans use smartphones, according to Nielsen. Though we've been teetering on that landmark tipping point for what seems like months, Nielsen's data says that we can call it official: 50.4% of us are using smartphones rather than feature ("dumb") phones. That's up a few ticks from December 2011, when 47.8% of Americans were using smartphones.

While this is a significant milestone for smartphone adoption, it's also one case where the details make for a more interesting picture than the larger story.

First, Apple sold more handsets (i.e., iPhones) than any other manufacturer in the U.S. Sure, Samsung may have just bumped Nokia from the top spot in total handset sales worldwide, but in the U.S., Apple sold the most smartphones, says Nielsen.

That doesn't mean iOS is the most widely adopted mobile platform, though. Android beats iOS handily, thanks to the wider availability of Google's operating system from a greater number of handset makers and wireless network operators around the country.

[ Nokia's Windows Phone is discounted in effort to spur sales. Read more at Nokia Lumia 900 Price Drops To $49. ]

The rundown goes like this: Android has 48.5% of the U.S. smartphone market, followed by iOS with 32%, BlackBerry OS with 11.6%, Windows Mobile with 4.1%, Windows Phone with 1.7%, and "other" with 2.1%. The "other" category probably includes Palm OS and webOS. The fact that Windows Mobile still trounces Windows Phone in the market is simply painful to watch: Windows Mobile is Microsoft's legacy mobile platform that the company has been phasing out, while Windows Phone is the more modern platform that just can't seem to catch a break. Perhaps the numbers will change once sales of the Lumia 900 are factored in later this year.

Drilling down further, 50.9% of women have adopted smartphones, just ahead of the 50.1% of men who've adopted them. (Does anyone else remember when smartphones--aka BlackBerrys--were used only by top brass/corner-office types?)

Looking at various ethnic groups, Asians are most likely a smartphone over a dumb phone: Nielsen's data shows that 67.3% of Asians/Pacific Islanders use smartphones. They are followed by Hispanics, with 57.3%; African Americans, with 54.4%; and finally, by Caucasians, with 44.7%. Yup, white people are the least likely to buy smartphones, according to Nielsen's calculations.

It should not surprise anyone that Americans aged 25-34 are by far the most smartphone-savvy--nearly 70% of them have smartphones.

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