How do we find out the Circle and the Mobile Operator for a number that's calling in? There is a hack available that provides this in a webpage, but we need this as part of the Exotel API.
If you have to do this inside an application, you could use our phone number lookup API. The DND tag in the response is what you are looking for.
You could also use this API to effectively do DND scrubbing. For all the numbers in your list, Repeatedly (with a time gap, say 3 seconds) query this API and based on the value of the DND tag, store it in a new list. The new list is now your list of DND-free phone numbers.
Sample PHP code for this DND scrubber is available in Github.