Apple's mobile products seem to be so popular that even older models are outselling the competition, according to reports from investment firm Canaccord Genuity.

The iPhone 3GS continues to outsell rival smartphones.

In a series of research notes sent to investors earler this week, technology analyst Michael Walkley shared his findings on how Apple fared in the mobile retail market in April. The analyst confirmed that the iPhone 4 was the top-selling smartphone at both AT&'T and Verizon last month, while iPad 2 sales stayed strong as consumers overwhelmingly chose it in favor of rival tablets.

But thanks to discounted prices, even the iPhone 3GS and the first-generation iPad are outselling the competition, according to Walkley. Specifically, the iPhone 3GS outsold both the Motorola Atrix 4G and the HTC Inspire 4G at AT&'T, while the 16GB and 32GB original iPads were sold out at Verizon less than two weeks following the debut of the iPad 2.

"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," wrote Walkley in his note. "We believe this highlights Apple's significant competitive advantage, and these older products help Apple offer a tiered pricing strategy at key channels and the older Apple products are still very competitive versus new competitor products."

Through his April retail checks, Walkely also confirmed ongoing issues with 4G-based Android smartphones, specifically related to their limited battery life when 4G is enabled. As a result, the HTC Thunderbolt, which enjoyed strong initial demand ran into slower sales and higher return rates in April, which in turn helped bump up sales of the iPhone.

As more Verizon customers upgrade over the next several quarters, Walkley believes, the iPhone will remain the top-selling smartphone at Verizon throughout the rest of the year. And at AT&'T, new Android smartphones are grabbing market share not from the iPhone but from Windows Phone devices. That trend has helped the iPhone remain a top seller and ensured strong demand for the iPhone 3GS, especially given its competitive price of $49.

Looking at the tablet market, the "modest sales" of the Motorola Xoom and RIM's BlackBerry Playbook were a sign to Walkley of the inability of those companies to replicate Apple's overall ecosystem and quality. With even Android smartphone users opting for the iPad over an Android tablet, the analyst expects Apple to continue its dominant lead in the tablet market this year and next.