I had an inkling these things existed (I’ve been in telco for a few decades), but the last ones I saw had nowhere near this scale. The amount of manual labor to put in the SIMs _and_ configure/remove the PIN codes must be staggering unless they get a bulk manifest of some sort (which you do get if you order batches of SIM cards for IoT applications), so expect these things to have a CSV import of some kind…
Plus I’m wondering what exactly are the radio capabilities of these things with so many antennae close to each other. Anyway, anyone doing network planning would hardly notice a few dozen registered subscribers unless they started generating traffic heavily (in which case they’d probably saturate one sector of a cell, but not with SMS and LTE…)
What a delightfully arcane rabbit hole to get into today, I’m going to do some research…