The bad news for Windows Phone market share continues: In a recent report, Windows Phone market share was so small in the U.S. that the well-known research firm Nielsen didn't even bother to break out its usage.

On its most recent blog post, Nielsenreports findings about smartphone use in the United States. It shows that smartphone use is at an inflection point: As of February, 50% of all mobile phones in the U.S. were smartphones. By next month, it's likely that the number will be more than 50%, because Nielsen reports that almost two-thirds of the people who bought mobile phones in the last three months bought smartphones.

The blog then goes on to report on smartphone market share. Of all U.S. smartphone owners in February, 48% have an Android phone, 32% have an iPhone, 12% have a Blackberry phone, and 8% have "other" smartphones. Windows Phone would be one of those in the "other" category.

There's even worse news for Windows Phone in the Nielsen numbers. Of those who bought a smartphone in the last three months, 48% bought Android devices, 43% bought iPhones, 5% bought Blackberries, and only 4% bought an "other" smartphone. So it's very likely that Windows Phone purchases in the last three months have been very anemic, and Windows Phone market share might even fall further.

Nokia has some big launches coming up of Windows Phone devices, notably the Lumia 900, due out soon. That may help increase Windows Phone market share. Whether it will be enough to lift Windows Phone out of the "other" category in Nielsen surveys remains to be seen, though.

This story, "Windows Phone Market Share is So Small, Nielsen Doesn't Even List It" was originally published by Computerworld .