IPhone app that blocks unknown numbers calling?

What apps blocks unknown numbers on iPhones? I don't care if you have to pay I just want one that works well.

Added (1). I'm NOT going to jailbreak my phone for this either.

There's Absolutely no app that does that without a jailbreak i know that for a fact

There are none. You block numbers through your phone provider. This is not something that you can do yourself on your phone, its through your actual service.

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