The Apple iPhone 4S is the undisputed smartphone champ, according to data collected by Canaccord Genuity. The firm examined individual handset sales across the top four wireless network operators in the U.S. between December 2011 and March 2012. The iPhone leads at AT&T, Sprint, and Verizon, although not at T-Mobile USA, where it isn't available.

"Our March checks indicated the iPhone continues to extend its market share gains," wrote Canaccord Genuity analyst Mike Walkley in a note to clients today. "In fact, we believe iPhones are outselling all other smartphones combined at Sprint and AT&T and selling at roughly equal volume to all Android smartphones at Verizon."

Given the number of other smartphones that are available from both AT&T and Sprint, that's quite an impressive feat. AT&T alone sells more than two dozen smartphone models. Some of the most notable models are the Samsung Galaxy Note (which has reached 5 million units sold all by itself), the HTC Vivid, and the Samsung Galaxy S II Skyrocket. The iPhone 4S alone is selling more units than those two dozen smartphones' sales figures combined. At Sprint, its non-iPhone device lineup is aging a bit, as the company has slowed down the rate at which it introduces new products.

[ Verizon was right on target, despite initial doubts about the iPhone 4's success. See Verizon Wireless CEO Claims Strong iPhone Sales. ]

The top three handsets by carrier for the month of March are as follows:

-- AT&T: Apple iPhone 4S, Samsung Galaxy S II, Samsung Galaxy Note.
-- Sprint: Apple iPhone 4S, Samsung Galaxy S II, Apple iPhone 4.
-- T-Mobile. Samsung Galaxy S II, HTC Amaze, Samsung Galaxy S Blaze.
-- Verizon: Apple iPhone 4S, Motorola RAZR/RAZR MAXX, and Samsung Galaxy Nexus.

Despite the iPhone 4S's leadership at the top three carriers, Samsung is obviously hot on Apple's trail with its own models. Samsung isn't popular just in the U.S., notes Canaccord.

"Our global checks also indicated another quarter of strong market share gains for Samsung, particularly in Europe and Asia," wrote Walkley. "In fact, we believe Samsung's strong smartphone portfolio across all price tiers will result in Samsung's smartphone shipments increasing a remarkable 15%-plus sequentially during the seasonally weak March quarter."

The iPhone 4S led at AT&T, Sprint, and Verizon in every month between December and March. Only time will tell what effect the next generation of Android devices will have on the iPhones 4S's sales lead in the months to come.

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