My solution was buying an old Avocent serial server. It's basically a giant raspberry Pi running a MIPS CPU. I should blog about this.

In the USA this is the best low-cost OOB Cell/LTE service I know of.

https://www.amazon.com/IoTDataWorks-Unlimited-12-Month-T-Mob...

It's off T-Mobile's network. Latency sucks unless you are close to the IP gateway they use (Chicago I think) but when shit's down and needs to get fixed it works.

I bought an old HP server for $150. It came with remote management built-in. Coupled with a cheap FQD and you can access it from anywhere.

Great job and has a VPN built in. All the components used lend themselves to monitoring too - Linux with monitoring-plugins, MQTT (doddle to watch from afar) and so on.

This also lends itself to remote monitoring and control of quite a few really big and expensive things that have serial ports.

I like the look of this ... pulls wires out of a discarded Pi experiment ...

Not a bad idea to have a BMC running software you can trust. We’ve recently made something similar from spare BeagleBone Blacks we had a few dozen of. Except it runs FreeBSD and also serves installation media (from the host point of view it looks like an USB flash drive).

You can build a wifi smart plug with an ESP8266 for 2 euro from aliexpress. A GSM module costs 2 euro.

A serial console over SSH with an old raspberry 1.

And the whole ensemble would take much less space.