Windows 10 / Windows Phone 10 is available for Majority of the devices running Windows Phone 8!
The Technical preview started with just a few Lumia devices and then it supported more Lumia devices.
Now you can get Windows 10 Technical Preview for all manufactures like HTC, Samsung, etc...
Follow the links below
I attended the Wednesday Build Windows keynote conference in San Francisco. And WOW! awesome event and love how Android and IOS Apps will be working with Windows 10 and Windows 10 for phones Yes that's the Universal Apps. This is HUGH for Windows Phone. Yes they will be having FlagShips Phones. Also love HoloLens was fricken innovative. It's like saying forget AppleWatch. Once Windows 10 gets finalized Windows phone 10 is going to take off great and for sure will have many users getting the phone. Sprint better start getting Windows 10 for phone when it becomes finalized and hope they will get flagships once it's available and just hope this happen.
I will never load any hemroid or iJoke apps on my phone but if that's what folks want go for it. The real question is how long will it take Samsung & Sprint (the maybe someday network) to actually give us the Windows Mobile update.