• by Mark Walsh  @markfwal, January 27, 2011

The iPhone may be about to launch on Verizon, but that won't stop Android's inevitable ascendence to the top of the U.S. smartphone market. The Google mobile operating system jumped from an estimated 6% of the market in 2009 to 24% in 2010, expanding across multiple devices and carriers.

In an upcoming report, eMarketer projects Android will carry that momentum through this year and next to become the leading smartphone platform in 2012, with a 31% share. That would put it one percentage point ahead of Apple, with BlackBerry-maker Research in Motion trailing further behind at 23%, and Microsoft at 13%.

The big shift comes this year when the current No. 1, RIM, drops from 30% to 25% share, while Android goes from 24% to 28%. eMarketer expects Apple to maintain its ground in the face of the Android onslaught, increasing from 28% to 30% this year to become the top U.S. smartphone OS in 2011. Android's continued climb will put it in a virtual tie for market leadership in 2012.

"With a growing roster of manufacturer and carrier partners in every major market and market segment, scale for Android is coming quickly in terms of device, market share, apps and ad revenues," said eMarketer principal analyst Noah Elkin in an article today previewing the report on mobile devices.

Separate data from comScore this month showed that Android had already overtaken Apple by the end of 2010, with 26% market share to Apple's 25%. But it also had RIM still comfortably in the lead, with 36% share. Android also ended the year by overtaking Apple's iOS as the leading smartphone platform on the Millennial Media mobile ad network, with a 46% share of impressions compared to Apple's 32% in December.

Apple will likely get a boost this year by ending its exclusive deal with AT&T for the iPhone and partnering with the nation's largest carrier. Verizon said it expects to sell 11 million iPhones in 2011 through the new alliance.

For marketers, whichever company ends up winning the smartphone wars matters less than making "the most of the growing number of smart devices to deliver rich, engaging experiences for consumers," according to Elkin. For the forseeable future, that mean Apple and Android will share center stage as the biggest mobile media platforms.