Google Android smartphone unit sales declined from 53 percent to 50 percent from the fourth quarter to the first quarter, thanks largely to the launch of Apple's iPhone 4 on Verizon Wireless.
Apple iOS share rose 9 percentage points to command 28 percent of smartphone unit sales for the quarter, according to NPD Group's new mobile phone tracker report. Research in Motion's BlackBerry operating system fell 5 percentage points to 14 percent.
NPD Group analyst Ross Rubin attributed the drop in Android handset sales to the Verizon iPhone, which helped cement the iPhone's position as the leading singular U.S. mobile phone brand.
Overall, Apple's iPhone accounted for 14 percent of the U.S. market sales, behind Samsung's leading 23 percent and LG's 18 percent share.
LG still pumps out an awful lot of feature phones, but Samsung's sales were no doubt helped by its hugely popular Samsung Galaxy S Android lineup, which sold more than 10 million units in its first handful of months of launch.
To wit, Rubin said that while the Verizon iPhone 4 chipped away at Android, handsets based on the open-source operating system still accounted for half all smartphones sold during Q1.
In a clear sign of just how dominant the iPhone and Android smartphones have become, Rubin said the top 5 smartphone handsets in the U.S. were, in order from highest to lowest: iPhone 4, iPhone 3GS, the Android-based Motorola Droid X, HTC Evo 4G and HTC Droid Incredible.
NPD's report comes two days after Nielsen pegged Android at 37 percent U.S. market share, compared with 27 percent share for the iPhone through March.
Considering the strong pipelines for both Apple's iOS and Android, and the lack of any real competitive threat from any Blackberry or Microsoft Windows Phone, there's no reason to think yet that iPhone and Android's dominance won't continue.
For the iPhone, it's the promise of cloud-computing sync with Macs and the iPad in the iPhone 5. For Android, the 4G LTE (Long-Term Evolution) networking perks from carriers are helping sell manufacturer's phones.
Verizon's HTC Thunderbolt 4G LTE smartphone shipped 260,000 units in a month, a success for any single Android handset, while the Samsung Droid Charge is a gorgeous, if not pricey ($299.99), 4G LTE device.
In time, sales of phones from both platforms should rocket with the successful implementation of NFC (near-field communication) capabilities, which should enable consumers to purchase goods with their handsets.