The research data from Nielsen was taken in the period from November of last year to January of this year and shows the smartphone marketshare for subscribers to a post-paid plan (which is, what I would guess, most smartphone users have). In the latest data, Android has taken a 29% share, surpassing both Apple and RIM, who both maintain a 27% share.
One very interesting detail revealed in the data is that Microsoft's smartphone offerings seems to be enjoying a 10% share, but it is unclear how much of that is due to the recent launch of Windows Phone 7.
If we look more deeply at the Android phone manufactureres, it becomes clear that HTC and Motorola are still the two main players in the U.S. market, but that Samsung seems to be making inroads (likely due to the Galaxy S line). With all the new handsets which were revealed at MWC last month set to release soon, I'd expect these numbers to change somewhat, but not much. The remaining share likely belongs to LG, Sony Ericsson, Dell, and Huawei.
Looking carefully at the graph above, it also appears that Android is now the most popular smartphone OS for individuals aged 18 to 24. In addition, smartphone ownership looks to be most prevalent for consumers aged 25 to 34.
The data does not show consumers below the age of 18, but due to the likelihood that most youths under 18 would likely have received their smartphone from their parents, it is possible that a large amount of those phones 'owned' by teenagers are factored into the figures of the parents, whatever their age group.
I think it would also be interesting to see the split in share among male and female. I have a nagging feeling that we'd see iPhones are significantly more popular among females, and that males are somewhat more inclined to choose Android phones.
Images from Nielsen