Hacker News Reader

that's not a cellphone network that's a VHF/UHF radio repeater network. basically same idea as ham radio hilltop repeater stuff in the US, but built for private purposes, and using COTS radios capable of basic encryption.

From the article:

Soldiers seized 167 antennas, more than 150 repeaters and thousands of cellphones and radios that operated on the system.

It sounds like it had both radio and cell bands if phones were able to use it.

There exist very fancy radios that look somewhat like GSM-alike cell phones, if I'm not mistaken.

there are also cheap vhf/uhf handheld radios from china which integrate a basic 2G GSM radio, SIM card slot, and can talk to common euro/asian 3GPP radio bands.

Also, there are lot of open source software in the space - no need to develop your own, just scan the code for backdoors.

In the 90s Colombian cartels were using mainframes.