[tamimio]

For 3G, it’s phased out, so the bands will be gone, you have to upgrade it.

The dial up part is far more involved, especially when they have auto answering connected directly to PLC or HMI, mostly with shared passwords. Also, you can’t trust the network operator either, insider threats and rogue employees are a threat. Additionally, dial ups are less monitored compared to modern network, and usually you end up with duct tape solutions like jump server to have strong authentication and continuous logging in firewall and such, plus proper encrypted tunnels so even physical wiretapping isn’t possible, and the assumption of air gap isn’t there because it’s reachable through public telephone, and the worst part, these dial ups are usually connected to windows XP Scada developers machines.

To add, obsolete is bad too, when your device cease to have vulnerability patches, you are screwed regardless of whatever configs you put.