Update at 2:52 p.m. PDT, with a report from AdMob about global Internet traffic on smartphones.
With the popularity of Apple's iPhone mobile-application store growing and competitors Palm and Google teeing up their efforts, the number of smartphone users tapping into mobile-application stores are expected to reach 100 million in 2013, according to a research report released Tuesday by In-Stat.
Currently, the number of smartphone users accessing mobile-application stores is roughly a fourth of the projected 100 million users and is largely comprised of only iPhone users.
These smartphones are built on an open platform that can accept applications from any developer who writes programs for that particular mobile operating system and are sold, or distributed freely, via a mobile-application store, rather than through the phone's carrier.
By 2013, Chamberlain said he expects nearly one-third, or 100 million, of all smartphone users to have the capability to access mobile-application stores. The current slice of the total pie is a fraction of that and largely comprised of Apple iPhones, he noted.
While a number of these mobile applications are offered for free, that could change as third-party developers and operators of mobile-application stores find it difficult to make money off advertising.
"If Coca-Cola buys a Superbowl ad, Nielsen can say how many people watched it," Chamberlain said. "But there are no independent third parties to audit mobile applications."
AdMob, a mobile-advertising marketplace, issued a report Tuesday that looked at February Internet traffic using smartphones.
According to the report, smartphones accounted for 33 percent of the global Internet traffic in February, up from a 26 percent slice six months ago.
And within the smartphone market, here's a ranking of which device grabbed the largest share of Internet traffic, according to AdMob:
And in the U.S., Apple's iPhone has an even greater share of the Internet traffic among smartphones.
The iPhone holds a 49.5 percent slice of U.S. Internet smartphone traffic, followed by Research in Motion's Blackberry 8300 with a 9.1 percent slice and the Blackberry 8100 with a 6.9 percent piece.
And among mobile operating systems in the U.S., AdMob ranks Google's Android as holding a 5 percent slice for the smartphone market. And holding the U.S. lead is the iPhone operating system with 50 percent of the market share in February.