Whilst US operators AT&T and Verizon dominate retail sales of Apple’s iPhone in the US, it appears that the Cupertino-based technology giant’s decision to slowly expand its store-in-store outlets via major US retailers is paying off.

A new report from Consumer Intelligence Research Partners (CIRP), which was shared with AllThingsD, suggests that Apple’s own iPhone retail sales are just a fraction larger than those of its partner Best Buy, which has been selling various iPhone models since 2008.

CIRP’s research — which accounts for sales in the three months ending February 2012 — ranks AT&T as the top iPhone seller, representing 32% of all iPhones sold in the US, with Verizon tracking its rival closely with a 30% share. The big-red carrier finally partnered with Apple and begun selling a CDMA-enabled iPhone 4 in February 2011.

Apple’s own sales account for 15% of sales — 11% in-store and 4% online — with Best Buy holding a 13% share, thanks to its 1100 stores, 600 of which hold an Apple store-in-store outlet. Unfortunately for Sprint, it has a 7% share, but the operator only recently became an Apple partner with the launch of the iPhone 4S.

iphone purchases by outlet 520x390 Best Buy proving almost as lucrative as Apple Stores for iPhone sales

Overall, retail stores were accountable for 76% of iPhone sales, with two thirds of iPhone 4S sales also made via retail outlets. It shows that whilst consumers are eager to ensure they can get their smartphone the minute it launches, many are happy to queue and enjoy the buzz around a proper retail store sale.

Walmart and Radio Shack also provide Apple store-in-store presences in the US, with a new Apple retail outlet opening recently in London’s Harrods.