The U.S. smartphone market is a fierce and competitive space, with winners and losers determined every month and new entrants always threatening to change the landscape.

Polling and channel checks by Canaccord Genuity analyst Mike Walkley reveal the that at the moment, the outlook is bright for Apple, which currently leads sales at AT&T and Verizon for both its iPhone 4 and the iPad 2.

Based on the trends, and the expectation of the iPhone 5 come September, Walkley raised his iPhone sales estimate for this calendar year to 77.3 million units from a prior 75.5 million, and raised his 2012 estimate to 100.2 million units from 94 million.

We believe the replacement cycle of this embedded base is also a powerful earnings driver for Apple, said Walkley, and he models a 40% replacement rate. That could mean 50 million units of iOS-based replacement sales this fiscal year, and 100 million in fiscal 2012, he projects, and 200 million in fiscal 2013.

Walkley also raised his 2012 iPad estimate to 55.1 million units from a prior 53.8 million.

But Apple isn't the sole winner.

On the Android side of things, Samsung's Infuse and Charge, based on Google's Android software, were top sellers at AT&T and Verizon, respectively.

HTC's Thunderbolt phone is still a top seller at Verizon, while the HTC Evo 3D, the Evo 4G, and Samsung's Epic were top sellers at Sprint.

Research in Motion

There are some losers, to be sure.

Research in Motion were not among the top three sellers at any of the four top U.S. carriers, Walkley notes.

Further, our checks indicated weak sales of the PlayBook tablet, he added. In fact, most of our checks indicate the similar pricing of the iPad 2 has resulted in limited sales of competing tablets such as the Playbook or Android tablets.

Walkley also opines that in Western Europe, Android phones are taking share from Nokia, rather than the BlackBerry scooping up that lost market presence. And in emerging markets, devices such as the 8520 from RIM are struggling as Nokia resorts to lower prices.

While Nokia's high-end smartphone Symbian sales are struggling during its transition to Windows, our checks indicate Nokia is very aggressively pricing its C-Series QWERTY keyboard messaging devices in international markets, pricing the C3 at perhaps $150 in Latin America versus $200 for RIM's 8520.

Motorola Mobility

As for Moto, the Atrix smartphone has struggled at AT&T against the Samsung Infuse and the HTC Inspire.

The Moto Droid X2, by contrast, had solid sales at Verizon, but it's still being outsold by the iPhone 4 and Samsung's Droid Charge, which is an LTE phone.

But the company is shooting itself in the foot with the incessant delays of the Droid Bionic. It's also hurting partners.

Motorola's anticipated 4G version of the Droid is going to lead to an even sharper share loss at Verizon, Walkley says, when it finally arrives, goes up against more 4G Android phones from Samsung and HTC, and the forthcoming iPhone 5.