Data released Thursday by comScore shows that Microsoft's average share of the U.S. smartphone OS market over the three months ended in June came in at just 5.8%, down from 7.5% from the three months ended in March, and down from 8% for the three months ended in January
The last number represents the first, full three-month period, as measured by Comscore, in which Windows Phone 7 devices were available--meaning Microsoft's share of the smartphone market has fallen 38% (from 8% to 5.8%) since the Windows Phone 7 launch. That's doubly troubling for Redmond, because the numbers also include Windows Mobile devices that are still in use. Actual sales are difficult to measure as Microsoft does not release such data.