Following today's Microsoft announcement of the upcoming Windows Phone 8 Update 3 (GDR3), Microsoft also introduced the Windows Phone Preview for Developers. Windows Phone Preview for Developers gives developers and early adaptors access to prerelease builds of upcoming Windows Phone updates on dev phones - before the operating system update is generally available to consumers. With the update in hand early, Microsoft hopes that developers (and early adaptors) can use the time to exercise their code on the update and verify that the apps works as expected. That said, the new Windows Phone Preview for Developers is now distributing the previously mentioned GDR3 to enabled dev phones.
To update a Windows Phone 8 to GDR3, users need to visit the Windows Phone Preview for Developers page. This page goes through everything users need to know about the preview program. Once terms and conditions are accept, the Windows Phone Preview for Developers app can be downloaded which installs from the Windows Phone Store directly onto the connected phone and allows to opt the phone in to receive updates. After that the update can be downloaded to the phone.
To participate, devs and/or early adaptors need to meet one of the three conditions: The phone is "developer-unlocked", users are a registered Windows Phone Store developer or a registered Windows Phone App Studio developer.
The update only includes the Microsoft portion of the update. Microsoft is not providing the firmware and drivers that are specific to the used device; the rest of the update will flow down to the phone when it receives the official update. When opted-in and applied for a prerelease update, users can only move forward with updates. When the update is publicly released for the device, the phone will once again be in a "released state". It's important to remember that there's no path back to a prior release/update.
After a preview update is installed, any warranty from the MO and/or OEM might be void.
Cheers ~ Arne