How far are your devices from a central point. I have 22 controllers spread out over 69 acres. I use Ubiquiti radios to connect to my office. I had considered 3g/4g but I am not a big fan of monthly revolving plans. So carriers you can request a public facing ip address for know additional costs, I have done this for cameras for one of my clients long ago with Verizon, but finding the right support person to talk to took time.
The ubiquity loco radios will work upto 7 miles away and cost about $50 each. So I have created a mesh and have my open sprinklers tied to them along with about 45 HD/4k Surveillance cameras which all tie in to my main network. I currently use AT&T Business for my internet with an Asus AC5300 for my router.
I don’t know your exact application but you may consider this option.