It's quite common to equip industrial PC's with a (PCI Express) (Mini) Card supporting LTE/HSPA+/GPRS (or even 5G if available).
This acts as a network card so you are just connecting to the internet, just like WIFI or a network cable.
You can use a SIM card from your favorite provider, some cards have two SIM slots where the second slot acts as a network backup in case the first provider network is unavailable.