It may come as a surprise to many, but Apple’s iPhone 4 and iPhone 3GS are the top two selling phones on the market in the US as of the third quarter.

A new study from NPD shows that Apple’s two previous models topped the list and were followed by the HTC EVO 4G, Motorola Droid 3 and the Samsung Intensity II. According to the report, price had a big part to play in buying decisions.

“Among U.S. consumers who considered purchasing phones in the $200 to $250 price range, 64 percent ended up purchasing a phone for less than $200,” the report reads.

NPD said that the share of U.S. mobile handset sales that were smartphones reached 59 percent in the third quarter of 2011, an increase of 13 percent since the same quarter in 2010. The report also noted that the average price for smartphones has fallen for four consecutive quarters and is now at $135.