HTC is making a version of its flagship HTC One phone with Microsoft's Windows software inside.
HTC said it developed the new model at the request of Microsoft, which has been trying to boost its Windows Phone system. The company will continue to make an Android version of the One, as well as other Android phones.
"By no means does this indicate we're moving away from Android," HTC spokesman Jeff Gordon said.
The Windows phone became available in the U.S. starting Tuesday through Verizon Wireless for $100US with a two-year contract and $600 without one.
HTC Corp. was the first company to release a phone using Google's Android operating system back in 2008, but it now lags behind Samsung, Huawei, Lenovo and other makers of Android phones despite critical acclaim for the HTC One.
HTC was also the first to release a Windows phone, in 2002, but it hasn't had a new one since 2012.
Gordon said HTC has been waiting until it had something strong enough to compete with Lumia phones from Nokia, a business Microsoft now owns. A mid-range device, he said, "would completely be overshadowed by the competition."
Windows Phone software now free
HTC also benefits from Microsoft's decision this year to give away its Windows Phone software for use in phones, as Google does with Android. The strategy reduces manufacturing costs for phone makers.
Yet the move comes as sales of Microsoft's phones are declining. In the second quarter, IDC said 7.4 million phones were shipped worldwide, for a 2.5 per cent share, compared with 8.2 million and 3.4 per cent a year earlier. Android's share increased to 85 per cent in that period. IDC said HTC had a worldwide market share of less than 2 per cent, the bulk for Android.
The Android version of HTC One is called M8, while the Windows version will be called M8 for Windows. The two look identical on the outside, except for a Windows Phone logo. Both sport metal exteriors and have screens measuring 5 inches diagonally.
HTC said Microsoft had to tweak its software to support the HTC One's features. For instance, the phone has a second rear camera to capture depth information so that users can later change which parts of images are in focus. Windows typically deals with a single rear camera.
HTC will also bring to the Windows phone its BlinkFeed hub for personalized content. But less-used camera features will disappear in the transition.