By Amy Gahran,

Worldwide, smart phones are booming. But they are still the norm. New statistics from Gartner in the recent sale of new phones. third quarter of 2010, 417 million new phones were sold – up to 35 percent in the third quarter of 2009.

Within these new phone sales, “smartphone sales grew 96 percent from the third quarter last year, and smartphones accounted for 19.3 percent of overall mobile phone sales in the third quarter of 2010,” Gartner said in a press release.

That sounds like a big deal, and indeed it is significant — but it’s important to put these figures in perspective.

Of those 417 million new handsets sold worldwide in third quarter 2010, 81 million (just under 20 percent) were smartphones, which Gartner defines as “communication devices based on open operating systems.”

It is significant, but not necessarily surprising, that this number jumped 96 percent over the previous year, given that 2010 saw an explosion of new smartphone products.

This is a bump in sales may indicate a pent-up demand for smartphones. But the problem with pent-up demand, which is difficult to predict how far it goes. This trend may continue until all of a smartphone – or can hit one of the many walls.

Here’s the big picture: Even though more consumers in more places than ever before now enjoy easy access to a broad array of smartphone choices, the vast majority (over 80 percent) of the new phones they’re choosing to buy are still feature phones. And that’s in the most recent quarter of this year — so expect those handsets to remain in use for at least another year or two.

Gartner’s numbers are global and so would include sales in places like China, Africa, and India — where most people cannot afford smartphones, and local wireless networks may not easily support that data traffic.

New mobile statistics from Comscore focus on the U.S. mobile phone market, which generally offers better conditions than developing nations for smartphone purchase and use.

Comscore looked at all mobile phones currently in use in the U.S. (not just sales of new handsets) during third quarter 2010. Of the top five mobile manufacturers whose handsets are in use in the U.S., only one was a smartphone (RIM, which makes the BlackBerry line of phones). Far more Samsung, LG, and Motorola models currently are used in the U.S. than any smartphone brand.

According to Comscore, about 25 percent of all U.S. mobile users currently have smartphones, which echoes Forrester’s figures from September.

RIM still leads this pack, with about 37 percent of the U.S. smartphone market, but that’s dipped slightly from three months earlier, while Android use showed the largest gain (6.5 percent) of any U.S. smartphone brand.

Economics are crucial for how most people purchase and use mobile phones — both initial costs, and monthly bills. I’d like to see statistics and trends on the current average costs to own and use mobile phones, comparing per-phone monthly costs for two-year contracts vs. month-to-month vs. prepaid, and overlaying that to compare feature phones and smartphones.

I suspect that right now typical monthly smartphone bills are still too high for most Americans, and that’s why feature phones remain popular.

If and when these monthly costs ever drop significantly, it will be interesting to see if other users are rushing to mobile smartphones – or if most people really just prefer simple phones.