While we've seen a variety of surveys pitting the iPhone against its most notable rivals, a recent study conducted by the NPD Group breaks down the numbers behind who left what phone (and what carrier) to acquire an iPhone. Not surprisingly, iPhone early adopters were "ten times more likely than other new phone buyers to have previously owned a Treo and three times more likely to have owned a T-Mobile branded phone, such as the popular Sidekick model." When it came to carriers, Alltel and T-Mobile were said to have lost the most customers to AT&T, as consumers who "switched carriers to buy an iPhone were three times more likely to switch from Alltel or T-Mobile than from other carriers." Notably, the lack of "corporate email support" was pinpointed as the main reason that many BlackBerry users didn't make the leap, but it did praise the iPhone for helping to "bridge the gap between consumer-focused feature phones and productivity-focused smartphones."