Windows Phone 7.8 is designed to give the Windows Phone 8 experience on devices which are not fortunate enough to get the Windows Phone 8 update, and there are a lot of such devices. But the good news is that the Windows Phone 7.8 is almost ready and you can expect the ROMs to drop by your door step any time now. But for those early adopters, there are always the beta ROMs available with which you can test out of the awesome features of the new operating system.
One such smart phone which will not be getting the Windows Phone 8 update but is scheduled to get the Windows Phone 7.8 update is the HTC HD7, a very popular Windows Phone smart phone. And today, it looks like your lucky day. There is already a beta release of the Windows Phone 7.8 ROM for your HTC HD7, if you are the kind of person who will download not so ripe ROMs and test them out.
The Windows Phone 7.8 beta ROM released bears the build number 7.10.8835.35, although it has its roots from a Tango 12180 dump from a Nokia device. So it is not yet fully optimized for the HTC HD7. But you can get your work done with it, more or less.
Proceeding with this will be at your own risk, nobody will be responsible if anything goes wrong with your smart phone during the process of updating the operating system, or after the process is complete. But most of the times, if you follow the instructions properly, nothing can possibly go wrong.
The Windows Phone 7.8 beta ROM for the HTC HD7 is available for download from the XDA Developers forum over here, if you are interested. All the best with the ROM and enjoy the new experience on your smart phone.