In terms of online dollar sales, flagship smartphones were significant revenue generators for US mobile carriers. Three of the four flagship phones (Apple iPhone, HTC G1, and BlackBerry Storm) ranked as the top revenue driver on their respective sites, despite being ranked just inside the top ten models in terms of unit volume. Meanwhile, Sprint's flagship phone, the Samsung Instinct, ranked lower than the others - number 7 in terms of revenue and number 15 by unit sales.

"Given what we saw with the other three carriers, it was surprising that the Samsung Instinct didn't rank higher in terms of sales or unit revenue on the Sprint site, particularly given its strong performance overall for Sprint," said Brian Jurutka, comScore vice president.

"This finding underscores some of the key differences between the online and offline sales channels, thereby giving carriers a better understanding of handset market dynamics and the actionable insights needed to modify their product offerings, messaging, and user experience depending on the channel."

BlackBerry Storm smartphone

Discounts and special offers continue to drive handset unit volume online, with US phone sales leader for AT&T actually being a refurbished version of the LG Shine. In fact, LG had the largest volume drivers on three of the four carrier sites, with the LG VX8350 on Verizon and LG Rumor on Sprint also ranking as the most popular models. The Motorola RIZR Z3 was responsible for the highest unit volume on the T-Mobile site. In each case, the vast majority of these phone models were provided to customers at no charge.

"Generally speaking, online is the place to go for free phones," added Jurutka. "The LG Rumor, in particular, was a huge volume driver on Sprint's site, with more than three times the unit volume of the next closest phone and 86 percent of the units being sold for free."

A substantial percentage of phones purchased across all carrier sites were free, an incentive that is typically offered to entice consumers to sign long-term phone and data plan agreements. A significant 75-percent of phones at the AT&T site were provided free, followed by T-Mobile (61 percent), Sprint (54 percent) and Verizon (48 percent).

"Many wireless consumers are having a tough time choosing between the budget-conscious handsets and the more expensive flagship phones at the top of many people's wish lists," said Andy Young, Director of Consumer Internet Sales & Marketing, Verizon Wireless.