That would be my first guess if the devices were found in the Middle East, but legitimate interconnect in the US is stupid cheap. (See e.g. Twilio's SIP pricing; I assume they have reasonable supply chain security.)

0.7 cents per minute for twilio. 47000 minutes in a month = $329/month if you run it around the clock.

Round-robining around some unlim SIM cards to stay below the radar will be cheaper.

Legitimate interconnect is presumably easier to get shut down, so I agree maybe not so much cheap as shady, as in a provider that knows their customers are likely to use the numbers for things that'd make them likely to lose a legitimate interconnect.

> legitimate interconnect in the US is stupid cheap

This is a to take advantage of "free calls to North America" provided by MVNOs, and free < cheap. Twilio starts at $0.01/min; 1 cent/minute x 200 lines results in a delta of $2.8k per day. I'm assuming a 20% utilization rate[1] on a device that holds 1000 SIMs

Further, it's a way to bypass STIR/SHAKEN requirements for a less-than-legitimate VOIP termination operations, which can attract paying customers that want to evade detection, typically criminal endeavors.

1. 20% utilization is pretty generous, but even if its 2%, not using Twilio is profitable at scale.