Canaccord Genuity’s Mike Walkley this morning writes that Apple’s (AAPL) iPhone 4S remained the top-selling smartphone in the U.S. cellular market in February, after the overall market accelerated its sales following a somewhat sluggish January.

“Our February checks indicated that iPhone sales remained strong in the U.S. and that sell-through of the iPhone led to additional market share gains versus its competitors,” writes Walkley.

In the U.S., Samsung Electronics’s (005930KS) “Galaxy S II” was also a strong seller, at AT&T (T), Sprint-Nextel (S) and Deutsche Telekom’s (DTE) T-Mobile USA. Motorola Mobility’s (MMI) “Droid Razr MAXX” was strong at Verizon Communications (VZ), and HTC’s (2498TW) “Amaze” and “Radar,” and Nokia’s (NOK) “Lumia 710” running Microsoft’s (MSFT) Windows Phone operating system.

Based on conversations at the Mobile World Congress trade show last week, and based on his supply chain checks, Walkley raised his global smartphone estimate to 695 million units this year from a prior 675 million-unit estimate, while cutting his feature phone estimate to 974 million units from 1.013 billion units.

Apple, he thinks, will have 8.6% of the global handset market by units this quarter, with Samsung having 23%, just behind Nokia at 24.8%.

Within smartphones, Apple will likely sell 32.6 million iPhones this quarter, for 23.7% share, perhaps just behind Samsung, at 33.5 million units, for 24.3% share. He models Apple’s “iOS” operating system having 23.7% share of units sold this quarter, versus total units based on Google’s (GOOG) “Android” OS having 52.7% market share. Windows Mobile may make up 7.1% of total units by operating system this quarter, he estimates. That would put it just behind Research in Motion’s (RIMM) BlackBerry OS in terms of platform share, with 8%.

Walkley sees continued share loss for RIM under newer “BB10” devices come out, perhaps later this year:

Our February checks indicated weak sell-through trends for RIM’s new BlackBerry 7 smartphones with weak Bold 9900 and Curve 9360 sales in many markets. While Curve 9360 sales are likely to remain weak given our expectations for more affordable Curve 9320 products shipping in upcoming months, the weak Bold 9900 sales lead us to believe Street estimates remain too high for RIM’s F2013. With increasing smartphone competition in all price tiers, we believe softer BlackBerry sales will continue during F2013, particularly with RIM delaying new BlackBerry 10 products until H2/C2012. While our meetings at MWC indicated RIM significantly increased its subsidies and sales and marketing expenses in key smartphone markets during the last two weeks of February, we believe BlackBerry sales will continue to decline until new products are introduced. In fact, our checks indicate consumers in high-tier smartphone markets prefer the robust ecosystems and high-end hardware of the iPhone and Android smartphones to BlackBerry devices.