I may as well toss in my two bits worth here. In the old days we would connect to systems over a dialup modem which is basically a serial port over a land line. Like Mike says most connections are done over IP these days.
And since we’re talking about dialup connections, you may run into a project where there’s no internet connection. In this case you can install one of these GSM modems, they operate over the local wireless phone network directly. No cable or fiber connection required.
You’ll need to order based on which country you are located and we’ll be sure to round up the correct model. You’ll also need to set up an account with the local carrier and add the sim card to this unit.