The US smartphone market has now boiled down -- at least for the immediate future -- to a three-way race between RIM, Apple and Android. Windows (Mobile) 7 is still a wild card, Palm's future is uncertain (notwithstanding HP's acquisition of the company) and Nokia (in the US) is a very long shot.

Nielsen recently reported data that reflected the following US smartphone market share distribution:

• RIM: 35%
• Apple: 28%
• Windows Mobile: 19%
• Android: 9%
• Palm: 4%
• Nokia: 2%
• Other: 3%

Nielsen says that almost 24% of US mobile subscribers now own smartphones and expects them to overtake non-smartphones by late 2011. Today comScore put out its version of that same data with a lower US smartphone penetration figure (21%):

Comscore also published market-share data for smartphones, which show all platforms flat to declining except for Android: 

Earlier this week Quantcast released data also showing that Android's mobile Internet browsing share had grown relative to the iPhone:

For comparison, here's StatCounter data for North America for the past 12 months, showing mobile OS share:

The data above show RIM gaining and the iPhone declining. However in this graph, Android is flat to down. 

In all the discussion and obsession over the competition between the iPhone and Android what's often neglected is how the other platforms in the US, save RIM, are almost in free fall.