Today Nielsen is reporting that Google's Android mobile operating system (OS) has beat out RIM BlackBerry and Apple iOS to become the number one mobile OS in terms of consumer market share in the U.S. Android has now reached 29% market share, compared with RIM's 27% and Apple's 27%. However, that's only one way to slice the pie.

Nielsen also notes that when looked at from a different angle - manufacturer market share, a way to break up the market by the handset makers' individual takes - it's Apple and RIM (each at 27%) who are clearly ahead. HTC is in 3rd place using that metric, with devices running Windows Mobile/Windows Phone (7%) and Android (12%).

This isn't the first time headlines touting "Android is #1" have been seen recently. In January 2011, analyst firm Canalys reported that Android reached the number one spot in terms of shipments worldwide, finally displacing Nokia from its longtime throne. Competing analyst firms questioned those numbers. They said they were seeing the same overall trends, but didn't believe Android had reached the number one position just yet.

Canalys had also previously claimed Android had reached the top position in the U.S. back in Q3 2010.

But all these numbers were tracking handset shipments, not consumer market share - that is, market share based on the phones actually purchased and used by end users. It's yet another way to slice the market share pie.

And there's a fourth way as well: profits. As independent mobile analyst Horace Dediu of asymco points out, with RIM and Apple, the two handset manufacturers that also make their own operating systems, "not only are the volumes higher, but so are the margins and hence the profit share."

Android More Popular with Young Consumers

In addition to general market share numbers, Nielsen also looked at buying trends among various age groups and found that those in the younger demographic were more attracted to Android. As always, Nielsen doesn't speculate as to why that is. But it could be something as simple as the more affordable prices of Android phones, at least in some cases. There are several mid-range to low-end Android handsets on the market that make for a decent enough "first" smartphone for feature phone/messaging phone upgraders.