Microsoft Dec-11 Jan-11 Feb-12 March-12 April-12 May-12 Jun-12 Jul-12 Aug-12 Sept-12 Oct-12 Nov-12 Dec-12 US installed base 4.7 4.4 3.9 3.9 4.0 4.0 3.8 3.6 3.6 3.6 3.2 3.0 2.9 Percent loss 0.5 0.2 0.5 0 -0.1 0 0.2 0.2 0 0 0.4 0.2 0.1

The latest Comscore numbers for the 3 months ending December 2012 (ie Q4 2012) is now out, and it shows a continuing decline in the number of Windows Mobile + Windows Phone users.

There are now 125.9 million smartphone users in USA, with WP + WM users accounting for 3.65 million users, 48,000 down from a month ago.

With the conversion rate from Windows Mobile to Windows Phone clearly being very low, this number will likely continue to drift down to the 2% market share of Windows Phone itself.

See the rest of Comscoreâ€™s analysis here.