I've a Airtel Mobile. But often I get useless calls from sales executives of different companies. I tried DND it worked for sometime. But now this sales executives call with their mobile numbers which cannot be restricted with DND, because DND only restricts call center number which are landline numbers.
Then there are some annoying people who keeps calling me like some annoying friends, colleagues and other persons, I don't want to receive their call specially when I'm roaming (it costs me money) and on Holidays.
So I searched on internet for a solutions and came across a very nice service from Airtel. Airtel Call Manager let one make block list numbers (numbers who will not be able to call me) and select list numbers (numbers which will only be allowed to call me).