To be able to blacklist people on a Windows Phone 8 device you need to have the GDR2 software up and running on it. You may still need an extra app, however. That is Nokia's call+SMS filter application, which is available on the WP Marketplace. When installed, it adds the blocking option to your handset's Phone app. Hold your finger on the number you need blocked until the menu appears and it should be right there. Or if you prefer, go to your Settings menu and scroll down to the very bottom. That's where the call+SMS filter section is. That's also where you remove entries from your list of blocked numbers. The call+SMS filter app is free and you can get it from
here.
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