A new NDP study reveals that the iPhone 4 and 3GS hold the top two positions in U.S. smartphone sales during Q3. The five best selling mobile handsets were as follows:

1. Apple iPhone 4
2. Apple iPhone 3GS
3. HTC EVO 4G
4. Motorola Droid 3
5. Samsung Intensity II

Apple’s had an identical ranking in NDP’s Q2 results.

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.

Other highlights:

• The average price for smartphones has fallen four consecutive quarters and is now $135 per device.
• The share of U.S. mobile handset sales that were smartphones reached 59 percent in Q3, a 13 percent increase quarter-over-quarter.