They do not make money from it. Actually, robocalls are really looked down upon in the industry, as the traffic is not profitable. Imagine this - telco carriers are charging per minute. No monthly fee, no setup fee, no per-call fees, only per minute with 6 second minimums and 6 second increments. Now imagine all the robocalls where they keep calls open for 3 seconds ( enough to determine if it's a live human or answering machine ). That carrier has a lot of resource utilization to "setup" a call, but after that, there is not much that the carrier needs to do.

In order to combat this, all tier-1 carriers now have ASR (answer ratio) and ACD (average call duration) minimums. In addition, if you have more than ~10% of your calls less than 6 seconds, you get an ADDITIONAL 1-2 cent per call surcharge. That's a lot of money given that my average cost of long distance is .17 cents ($0.0017) per minute.

It's the second tier carriers that is "blending" this traffic with good traffic in order to get the minimums then charge the telemarketers much higher costs per minute.