The latest U.S. smartphone market share numbers are out from comScore Networks this morning, showing Microsoft posting a slight gain in mobile subscribers for the three months ending in May — up one-tenth of a percentage point to 4.0 percent, compared with the three months ending in February.

The result follows the launch of the flagship Nokia Lumia 900 Windows Phone in the U.S. in April.

No, it’s not exactly a blockbuster outcome. Microsoft remains well behind Google, Apple and even struggling BlackBerry maker Research in Motion in the rankings. In addition, compared with Microsoft’s result for the three months ending in April, the 4.0 percent market share for May is unchanged.

However, the trend is better than the regular declines the company had previously been experiencing.

Two years ago, in May 2010, Microsoft was third in the comScore rankings with 13.2 percent market share. Google at that point was fourth, with 13.0 percent market share for Android. Google has since seen that number skyrocket to more than 50 percent of the market, ahead of Apple at 31.9 percent.

Microsoft’s numbers include legacy Windows Mobile users, so the trends aren’t a pure representation of the new Windows Phone OS.

Microsoft last month unveiled Windows Phone 8, the next version, shipping later this year. It won’t be available as an upgrade for existing Windows Phone 7 devices, but the company will offer a separate version, Windows Phone 7.8, with an overhauled home screen similar to Windows Phone 8.