Microsoft apparently asked HTC to put Windows Phone in more HTC phones. Specifically in Android phones. According to a report from Bloomberg, the head of Microsoft's operating systems unit Terry Myerson asked HTC to "load Windows Phone as a second option on [Android] handsets."

The talks with HTC are still in its early stages so no one is sure what the deal will end up looking like. Bloomberg says:
The technical details have yet to be ironed out. It wasn’t clear whether an HTC phone would run Windows and Android at the same time, or let users choose a default.
It would be nice to see how Windows would look like on an HTC One for sure. HTC has made Windows Phones before, but what if they were to just install the OS in Android phones? Would that increase its market share? [Bloomberg]