@adrian78666: it’s good you mentioned FONA from Adafruit. I was just thinking about a serial to GPRS adapter and it looks like this is what FONA is. Basically you can use the serial interface to communicate and send command to the shield. This is much easier to work with compared to shields based on SPI, which requires a major overhaul of the firmware. I have never used FONA, but I think this is probably among the easiest way to add cellular connectivity to OpenSprinkler.