WPCentral has images and new info on GDR3.
Windows Phone 8 GDR3 is OS Build 10484.
Later this year, towards the November time frame, Microsoft is rumored to be releasing Windows Phone 8 General Distribution Release 3 (GDR3) along with alleged new firmware from Nokia named “Bittersweet shimmer” (originally reported by the site Nokiapoweruser). The OS update will once again enable new hardware features like advanced Qualcomm processors and 1080P display resolution, but it will also have numerous enhancements for current devices. The release will coincide with the availability of Nokia’s Lumia 1520 with a 6-inch display.
Tonight, a poster in the Windows Phone Central Forums with the handle xs2k has posted alleged screenshots running Windows Phone 8 OS Build 10484, supposedly taken from a Lumia 920 developer device picked up on Craig’s List.
Update 2:30 AM ET: Windows Phone Central has learned of some additional features found in GDR3 through an additional source, unrelated to xs2k
Custom sounds for text, voice mail, e-mail, and reminders
Restore over Wi-Fi when you reset your phone
Huge amount of work on Bluetooth with various vehicles and devices
Update 2:30 AM ET: We have secondary confirmation that these images and features are authentic.