Not true. DND works great in India. You can also report a spam call or an SMS and your mobile network provider has to provide a resolution. They usually do it by banning that abusing number.
But don't they just "call" from a different number? Or a random number each time? There's no real verification on the number being called from - its specified _by_ the caller a lot of the time.
So unless the phone company starts banning phone companies that don't enforce correct caller id, it won't do anything.
> So unless the phone company starts banning phone companies that don't enforce correct caller id, it won't do anything.
But it evidently does do something, since now it's confirmed in these threads that at least 4 (possibly) more countries do have these lists, and they do work.
DND is available both on Android and iOS.