Developer “Walking Cat” has made an interesting discovery by comparing the Windows Phone 8 emulator code vs the Windows Phone 8 GDR2 emulator code.
It appears the software contains brand-new APIs for call and SMS blocking and filtering, with the ability to block specific numbers, phone numbers which are not in your address book and even phone calls with private numbers.
The same capability is available for SMS messages, which would certainly be good for those harassed by others.
It seems the capability can be activated and deactivated by carriers, and as far as we know there is no interface for these APIs in already released GDR2 handsets such as the Nokia Lumia 925 and 1020. It may be possible for 3rd party developers to access the API however, which would be a great new feature to exploit.
See the code at Pastebin here.