Where’s Windows Phone? Despite a push to get its mobile platform into the hands of more consumers, Microsoft’s share of smartphone subscribers in the U.S. continued to decline as 2012 drew to a close, according to numbers released this afternoon by the comScore Networks research firm.

The result is notable in part because new devices running Windows Phone 8 debuted for the holiday quarter.

Microsoft had 2.9 percent of U.S. smartphone subscribers for the three months ended in December, down from 3.6 percent for the September period. The December result compared to 53.4 percent for Google, 36.3 percent for Apple and 6.4 percent for Blackberry, according to the comScore Numbers.

The comScore numbers track total subscribers, not new purchases, so part of Microsoft’s decline can be attributed to the gradual fading of the company’s previous Windows Mobile platform. However, the trend also suggests that Windows Phone isn’t yet gaining the traction that it would need in the U.S. to become a solid No. 3 in subscriber market share.

Here’s the full comScore chart, with additional data available in this news release.

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