Blacklisting the numbers

Yes. You can call the call centre and request for it.If you are a Post-paid subscriber the chances are higher.I had got it done in Airtel
 
some phones have this feature. htc sense for example had this feature on one x. i would imagine there should be apps out there for android/symbian which can do that as well. for featurephones you would have to check if your mobile operator has a service for it.
 

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