Blacklist for incoming calls for Motorola U9. Any?

[mto]

Hello, I am in need of an app whick blocks incoming calls by number/caller ID. Specifically, I don't need a just muted ring tone, rather I want my phone to be recognized as unreachable / not connected.
Does such an app exist for the Motorola U9? If not, which are the cheapest mobile models allowing for the above functionality?

Thanks for helping,
MTO

[beeplus]

such an application does not exist on U9