Many scammers use internet telephony to call someone and some even spoof the caller id. In India, the mobile companies request subscribers to report any international call which shows local spoofed caller ids to them, so they can investigate it. So I am guessing it is trickier than we believe to track them ...
Can they at least flag calls as being from voip?
If it is local, they probably can. But VoIP being international is the problem. See Why in the year of our lord 2022 am I still getting robocalls??? - https://www.vox.com/recode/22882647/robocalls-robotexts-scam... ...
Unfortunately it's paywalled, but... International in which way? The actual connection from the voip system to the POTS must be inside the country I thought. And if it's not, there has to be some telco-operated gateway to whichever country it's in. Sure the end person using it is in another country connecting via internet, but there must be some local entity to go after.