In a news article titled "America's most Popular smartphone is not the iPhone" by IDC, Apple iPhone Q1 market share was 19%, down from Q4's 26%. The biggest winner is the BlackBerry. Surprisingly, even Palm had a great quarter at 13% (up from 7.9%). IDC pointed out that the iPhone may not have done as well due to the fact that it is sold exclusively through one vendor.
I would read a little into these figures before jumping to the conclusion that "BlackBerry is the most popular smartphone". 1). in Q1, I think Apple arbitrarily held back in iPhone production in preparation for possible new release of 3G iPhone next week. As I recall, there has been a major shortage of iPhones throughout Apple stores everywhere. The drop in sales has something to do with the lack of supply; but it doesn't translate into lack of interest from consumers; hence the word popularity doesn't supply. 2). BlackBerry has long been adopted into the business community. It has become the gold standard in corporate email communication. A big percentage of its sales would come from business accounts (new handsets as well as renewal).
A true measure of popularity should come about in Q3 (assuming there will be a 3G iPhone release next week and a good supply to handle market demand).