Please watch your tone and choice of words. That sentence is more focused on defaming the OP than addressing the merit of what they said.
Furthermore, saying "it makes no difference to the scammers if they're paying 10c per minute or calling for free" shows an equally clear failure to understand the economics of these scams. The vast majority of calls made by a scammer will yield nothing. They have to make numerous calls to find the one sucker who can be convinced to turn over their financial information or mail cash or do whatever needs to be done. I don't know the exact per-minute cost at which most scams become cost prohibitive, but I'm pretty sure you'd be shocked at how little it is. If it takes 2,000 calls to find one victim, and you're paying 10 cents per call, you'll spend $200 per victim. Will you make that much back, and will it be enough to offset all of the other costs involved in trolling? It depends. But it definitely makes it less appetizing than when the calls are free.