Use any of this Samsung Mobile units they have this features
G800, G810, U600, U800, U900
go to setting
then choose call setting
then all calls
turn Auto reject call "on"
go to reject list
tick "unknown"
and the rest of unwanted numbers you can put them under your reject list.
then you will never receive anymore unknown or any unwanted numbers.
you will still receive International calls that store in your phone. this is what I do, if I don't wish to receive any calls from strangers.

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