With the release of Windows Phone 8.1 Update 1 Microsoft has unlocked their OEM site describing the details of the Windows Phone 8.1 GDR1 update.
Most of the information has already been leaked, but the minutia of the changes are now available, and includes interesting titbits, such as that it is now possible for OEMs to create a Windows Phone system image that is stripped of all phone functionality, “intended only for devices that will not be connected to a cellular network” and that the 100 MB update download limit is in fact configurable and can presumably be changed by an OEM.
