The No. 1 smart phone sold at both AT&T and Verizon in April was the iPhone 4, according to news reported by Electronista. Also selling “very strong” was the iPad 2.

According to Canaccord Genuity analyst Mike Walkley, the iPhone 4 was the best selling smart phone in the U.S. in April. Walkley’s assessment is based on unspecified “checks” of Apple business. Apple, AT&T, nor Verizon report on monthly sales numbers.

Walkley also believes existing Apple owners, in particular those owning an iPad, will remain with the company over the long term because of the company’s “higher price points for tablet applications.”

This refers to a tendency of people to be less willing to consider alternatives to the iPad because of the money spent on iOS tablet apps.  As any iPad owner will confirm, apps for the tablet iDevice are typically more expensive than Universal or iPhone/iPod touch-only apps.

Finally, Walkley approximates Apple’s worldwide iOS install base at the end of fiscal year 2011 (in September) to be 246 million units. The company began the year with 189 million active iDevices sold.

In 2012, Walkley anticipates that number will grow to 404 million. As a comparison, the current population of the U.S. stands at 311 million.

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