I'm seriously wondering about the practicality of this operation. Wouldn't that many SIMs on the same spot overload any nearby cell tower? And even if the antennas could stand the load, that many SIMs hugging the network without any logical reason (like a parade or a demonstration) is bound to raise alarms at the network operator HQ. If this is a scam operation, I would expect these boxes to be distributed across several locations.

It's likely a "crime-web" service host. They are probably somewhere in Manhattan or Brooklyn to have enough tower cells to handle it (tis the benefits of a dense city for this type of operation). They probably gradually grew it as their crime web demand rose and flew too close to the sun.

It also sounds like they did have multiple locations, but they didn't distribute the modems out enough to flew under the radar longer.