It was somewhat clear that sooner or later some developers will find a way to bring the recently launched Windows Phone 7.1 Mango upgrade to everybody; which was supposed to be available for registered and approved Microsoft Windows Phone developers only - who paid US$ 99 to get some early Beta love. But heck, I haven't expected that it comes that fast. As windows phone hacker reported yesterday, a workaround was made available which allows to flash Mango to any Windows Phone 7 device, doesn't matter if developer or just user. As expected, Microsoft's way to distribute Mango to developer devices is redirecting registered devices to a special update server, instead of using the public one for regular updates.

The workaround seems to modify some registry entries on the non-Mango Windows Phone which allows Zune to search on the Mango update server for available updates, instead of searching on the public update server.

The update process seems to be fairly straight forward and only requires the proper Microsoft Windows Phone Support Tool and a Batch file. The Batch file is executed, the device is back-uped and updated with the the changed Registry keys, Zune jumps in, downloads Microsoft's Mango Beta and is flashing it to the connected device, that's it.
As always, there's neither a warranty given that the workaround either works nor bricking the device, nor to talk about the question of law. Especially because regular end-users will get the Windows Phone 7.1 Mango upgrade later which year free of charge anyway.
Cheers ~ Arne