The device is probably 256 of those, or similar, chipsets on a board with integrated SIM slots and connectors for SMA antennas. You'd have a hard time producing something like this cheaper than China.
There's only 64 antennas but 256 SIMs, so there are either 64 separate quad-SIM modems (AFAIK only Mediatek made those, and in 2G only) or it's just one big FPGA, managed by a small CPU and connected to a bunch of RF ICs, like the inverse of a base station.
