Latest update for Extras + Info service app will now let you block calls and SMS. But there is a catch, call and SMS blocking function will only work on those Lumia devices which are running on Amber update or GDR2.
This was made possible because of API integration which comes with W8 GDR2 update. And Nokia was able to add Call and SMS blocking feature to their latest Lumia smartphones. At this moment, only Nokia Lumia 1020 and Nokia Lumia 925 have this feature. Other models (920/820/720/620/520) will soon get this update.
If you wish to get this function and are running WP8 with GDR2 on your Lumia then you can simply do it by navigating to Settings > Extras + Info and you’ll find the Call and SMS filter. Add the numbers you wish get ignored automatically.
There is the link for the app, you can visit the store and install it straight away. Extras + Info Nokia Store