So I have this Raspberry Pi cluster that is connected to a SONOFF S20 WiFi plug that has custom firmare on it. I can ping that plug using Linux and curl to power on/off my cluster. But I want to be able to power it on from GPRS without having to open up a VPN in my router and use WiFi.
That is how I came up with the idea of using an Arduino R3 WiFi board (because it can take 5V) and a SIM800L module (also 5V caable). I've fashioned a custom enclosure for this project and it all fits in nicely. The theory is that I can SMS the SIM card in the module to send a "power-on/off" command via the Arduino's WiFi to the SONOFF S20 WiFi plug.
(will update as I make progress).