You might recall that last week a Nokia Lumia 920 purchased from Craig's List contained the GDR3 and Bittersweet shimmer update. The update allows Windows Phone users to shutdown open apps by tapping on an "X" and lock the screen in either portrait or landscape orientation. A Driving Mode will automatically disable certain features of the handset while the user is driving a vehicle.
The GDR3 and Bittersweet shimmer update is expected to debut on the first Windows Phone phablet, the Nokia Lumia 1520. The 6 incher will supposedly be unveiled on September 26th and launched October 22nd.
source: WinPhoneViet (translated) via WMPoweruser