It's been an interesting month for Windows Phone, what with the release of Windows Phone 8.1 and the announcements of several new handsets. How have these developments impacted Windows Phone usage for the month? As always, AdDuplex provides an interesting peek at which Windows Phone handsets are used the most.

As you may remember, AdDuplex bills itself as the largest cross-promotion network for Windows Phone and Windows 8 apps, empowering developers and publishers to promote their apps for free by helping each other. And each month it provides a tantalizing glimpse at which Windows Phone (and Windows) devices people are actually using.

Some trends from this month's report include:

Lumia 520 is still on top ... but the growth is over. Nokia's mighty-mite Lumia 520 continues to dominate the usage charts, coming in at 34.3 percent overall worldwide this month. (Or at about 38 percent, if you add in the variants.) But the year-old device has finally stopped growing, AdDuplex reports, and this is the first time they've not seen a month over month gain in Lumia 520 usage. Still, it's been an amazing run to the top, and it will be a while before the 520 gives up its crown. The number two most frequently used device, the Lumia 625, only has 6.4 percent share.

Nokia goes out on top. In its last month as a standalone entity, Nokia commanded fully 93.5 percent of all Windows Phone handsets in use, compared to just 4.4 percent for HTC, 1.3 percent for Samsung and 0.8 percent for Huawei.

Windows Phone 8.1 debuts. Released just a week before AdDuplex took its survey, Windows Phone 8.1 already commands 3.1 percent of all Windows Phone usage, compared to 78 percent for Windows Phone 8 (or a combined 81.1 percent usage for Windows Phone 8.x) and 18.9 percent for Windows Phone 7.x.

Several new Lumias are on the way. AdDuplex is seeing several Lumias in the usage survey, including several 1080p devices with 5 inch screens that are almost certainly the Lumia 930 in various markets, plus the RM-1010, and the RM-1020 and 1027, the latter of which both sport 480 x 854 screens. No sign of the Lumia 630 or 635.

Note: I guess I forgot to post a device stats article for March. Doy!