The Windows 10 phone O/S was tested by Redmond Magazine as described in article below

http://redmondmag.com/articles/2015/04/14/first-look-at-windows-phone-10.aspx

We’re getting closer to the much anticipated release of Windows 10 and the gifts from Redmond just keep coming. Recently, Microsoft announced a preview of what many are referring to as Windows Phone 10 (the more official name seems to be Windows 10 for Phones).

The initial preview release is somewhat limited in that the OS will only run on specific models of Windows phones. I couldn’t risk installing the preview on my “production” phone and none of my lab phones were supported. Some Web sites have published hacks for installing Windows Phone 10 onto unsupported devices, but I didn’t want to risk bricking a lab phone. Besides, I wanted to experience the preview as Microsoft intended. Uortunately, there was an easy solution. I was able to get an AT&T Nokia Lumia 635 No Contract GoPhone from Amazon for under $50. Upon receiving the device I was able to install the Windows Phone preview onto it very easily.