In a note to clients — as reported by “AppleInsider” (http://www.appleinsider.com) — Canaccord Genuity technology analyst Michael Walkley says older iOS products sold at a discounted price, like the iPhone 3GS and first-generation iPad, are often more popular than newer devices running the Google Android operating system.

The iPhone 4 is “by far” the top selling device at both carriers AT&T and Verizon, he says. However, Apple’s older devices continue to be strong sellers.

“Interestingly, our April checks indicated continued strong demand for the iPhone 3GS at AT&T and iPad 1 at Verizon, as these older generation products with reduced prices often outsold new Android products,” Walkley writes. “We believe this highlights Apple’s significant competitive advantage, and these older products help Apple offer a tiered pricing strategy at key channels.”

Checks with Verizon stores found that the 16GB and 32GB versions of the first-generation iPad sold out in less than two weeks after the iPad 2 rolled out, he adds. And at AT&T stores, the $49 iPhone 3GS outsold newer phones like the HTC Inspire and Motorola Atrix.

Walkley says that checks with stores found that new Android smartphones were largely gaining share from Windows 7 smartphones, but not the iPhone. Walkley also expects the iPhone to remain the top selling handset at Verizon throughout 2011 as upgrades continue.