I'm not literally knowledgeable, that's why I'm asking
I have some other knowledge, which is quite applicable I guess, but anyway. I just installed the 'ifconfig' app from the android store so I could see the interfaces (without having to log in via adb shell, which I was imagining would add its own interface(s) and so confuse the issue). That's how I can tell what interfaces go UP (ie have IP addresses assigned) when I do different things, like enable cell data (rmnet0 goes up) or enable hotspot (rmnet1 goes up, as well as wlan0).
I had previously assumed that rmnet* interfaces represent different sim cards, so perhaps phones can have more than just two (that's the maximum I've ever seen in a phone); but this shows that they aren't actually like that, though they seem to be data connections over cell networks.
I'm considering getting a 3 sim for my home broadband, so trying to understand the pit-falls of this route. I'm wondering what the differences are between a data sim and a regular sim. Can I put a data sim in a phone and use it for a modem? Can I put a normal sim in a 'mifi' device and use it only for data (and move it to a phone when I have visitors who want to use it for phone calls too)?
I guess those are all different questions...