Platinum Contributor III
It uses a feature called dual ring.
This allows an incoming call to ring simultaneously on two numbers.
So the nomorobo service has to see the incoming ring.
This happens the same time both for them and on your phone.
If a forum member gives an answer you like, give them the Kudos they deserve. If a member gives you the answer to your question, mark the answer as Accepted Solution so others can see the solution to the problem.