The data comes from a new report available from Consumer Intelligence Research Partners, which provided a copy to AppleInsider on Wednesday. Its research found that 80 percent of AT&T iPhone buyers and 85 percent purchasing Apple's iPhone for use with Verizon were already subscribers to those respective carriers.
But just 67 percent of iPhone users with Sprint were already customers of the nation's third-largest wireless provider. Among Sprint iPhone users, 9 percent switched from AT&T, 2 percent switched from Verizon, and 5 percent came from T-Mobile.
The largest share of customers switching to Sprint came from outside the "big four" wireless providers in the U.S. CIRP's research found that 16 percent of Sprint iPhone buyers fell under the "other" category, which is primarily made up of pre-paid carriers.
That means that a third of iPhone users on Sprint came from other carriers and are new to the company. That's more than twice the percentage of new customers gained by Verizon via iPhone purchases.
Research via Consumer Intelligence Research Partners.
The survey of Apple customers also found that AT&T and Verizon were able to retain 94 percent of their existing customers that bought an iPhone. Sprint was slightly behind, retaining 88 percent of its existing customers, but 10 percent of those Sprint lost switched to AT&T.
AT&T also gains the greatest number of switchers from T-Mobile, which is the fourth-largest wireless carrier in the U.S. CIRP's survey found that 65 percent of T-Mobile users who bought an iPhone switched to AT&T, compared to 26 percent leaving for Verizon and 10 percent for Sprint.
Previous research from CIRP released in March showed that retailer Best Buy sells nearly as many iPhones as Apple does through its own direct sales, and that customers prefer to buy their iPhone in person rather than online.